From: Zhaoyang Huang <[email protected]>
Kernel linear mapping will be split to the smallest granularity when
RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
to apply PTE_CONT on pte.
Signed-off-by: Zhaoyang Huang <[email protected]>
---
arch/arm64/Kconfig | 9 +++++++++
arch/arm64/mm/mmu.c | 10 ++++++++--
arch/arm64/mm/pageattr.c | 9 +++++++++
3 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fee914c..3f8fbf0 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
This requires the linear region to be mapped down to pages,
which may adversely affect performance in some cases.
+config RODATA_FULL_USE_PTE_CONT
+ bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
+ depends on RODATA_FULL_DEFAULT_ENABLED
+ default y
+ help
+ Apply PTE_CONT on linear mapping as much as we can when
+ RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
+ impaction on performance by small pte granularity.
+
config ARM64_SW_TTBR0_PAN
bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
help
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index cfd9deb..8017b17 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
* The following mapping attributes may be updated in live
* kernel mappings without the need for break-before-make.
*/
+#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
+#else
+ pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
+#endif
/* creating or taking down mappings is always safe */
if (old == 0 || new == 0)
return true;
/* live contiguous mappings may not be manipulated at all */
- if ((old | new) & PTE_CONT)
+#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
+ if (old | new) & PTE_CONT)
return false;
+#endif
/* Transitioning from Non-Global to Global is unsafe */
if (old & ~new & PTE_NG)
@@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
/* use a contiguous mapping if the range is suitably aligned */
if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
- (flags & NO_CONT_MAPPINGS) == 0)
+ (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
__prot = __pgprot(pgprot_val(prot) | PTE_CONT);
init_pte(pmdp, addr, next, phys, __prot);
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index a3bacd7..88a87eb 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
pgprot_val(clear_mask) == PTE_RDONLY)) {
for (i = 0; i < area->nr_pages; i++) {
+#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
+ unsigned long cont_pte_low_bound;
+ unsigned long addr;
+
+ addr = (u64)page_address(area->pages[i]);
+ cont_pte_low_bound = addr & CONT_PTE_MASK;
+ __change_memory_common(cont_pte_low_bound,
+ (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
+#endif
__change_memory_common((u64)page_address(area->pages[i]),
PAGE_SIZE, set_mask, clear_mask);
}
--
1.9.1
On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
>
> From: Zhaoyang Huang <[email protected]>
>
> Kernel linear mapping will be split to the smallest granularity when
> RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> to apply PTE_CONT on pte.
>
> Signed-off-by: Zhaoyang Huang <[email protected]>
How would this lead to TLB pressure, and how does the use of
contiguous mappings mitigate that? The linear mapping of the kernel is
rarely used, as all normal accesses to it go via the vmalloc region,
so in which case would TLB entries be allocated for this region in a
way that could cause a measurable performance impact?
> ---
> arch/arm64/Kconfig | 9 +++++++++
> arch/arm64/mm/mmu.c | 10 ++++++++--
> arch/arm64/mm/pageattr.c | 9 +++++++++
> 3 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index fee914c..3f8fbf0 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> This requires the linear region to be mapped down to pages,
> which may adversely affect performance in some cases.
>
> +config RODATA_FULL_USE_PTE_CONT
> + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> + depends on RODATA_FULL_DEFAULT_ENABLED
> + default y
> + help
> + Apply PTE_CONT on linear mapping as much as we can when
> + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> + impaction on performance by small pte granularity.
> +
> config ARM64_SW_TTBR0_PAN
> bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> help
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index cfd9deb..8017b17 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> * The following mapping attributes may be updated in live
> * kernel mappings without the need for break-before-make.
> */
> +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> +#else
> + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> +#endif
>
> /* creating or taking down mappings is always safe */
> if (old == 0 || new == 0)
> return true;
>
> /* live contiguous mappings may not be manipulated at all */
> - if ((old | new) & PTE_CONT)
> +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> + if (old | new) & PTE_CONT)
> return false;
> +#endif
>
> /* Transitioning from Non-Global to Global is unsafe */
> if (old & ~new & PTE_NG)
> @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
>
> /* use a contiguous mapping if the range is suitably aligned */
> if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> - (flags & NO_CONT_MAPPINGS) == 0)
> + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
>
> init_pte(pmdp, addr, next, phys, __prot);
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index a3bacd7..88a87eb 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> pgprot_val(clear_mask) == PTE_RDONLY)) {
> for (i = 0; i < area->nr_pages; i++) {
> +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> + unsigned long cont_pte_low_bound;
> + unsigned long addr;
> +
> + addr = (u64)page_address(area->pages[i]);
> + cont_pte_low_bound = addr & CONT_PTE_MASK;
> + __change_memory_common(cont_pte_low_bound,
> + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> +#endif
> __change_memory_common((u64)page_address(area->pages[i]),
> PAGE_SIZE, set_mask, clear_mask);
> }
> --
> 1.9.1
>
On Mon, Nov 22, 2021 at 4:52 PM Ard Biesheuvel <[email protected]> wrote:
>
> On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
> >
> > From: Zhaoyang Huang <[email protected]>
> >
> > Kernel linear mapping will be split to the smallest granularity when
> > RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> > to apply PTE_CONT on pte.
> >
> > Signed-off-by: Zhaoyang Huang <[email protected]>
>
> How would this lead to TLB pressure, and how does the use of
> contiguous mappings mitigate that? The linear mapping of the kernel is
> rarely used, as all normal accesses to it go via the vmalloc region,
> so in which case would TLB entries be allocated for this region in a
> way that could cause a measurable performance impact?
In fact, the patch is about to use PTE_CONT *OUT OF* the range of
kernel text. Would you please have a look at the code. It apply
PTE_CONT during map_mem and then clear it when load_module change the
corresponding linear mapping to the area it use in vmalloc area.
>
>
> > ---
> > arch/arm64/Kconfig | 9 +++++++++
> > arch/arm64/mm/mmu.c | 10 ++++++++--
> > arch/arm64/mm/pageattr.c | 9 +++++++++
> > 3 files changed, 26 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index fee914c..3f8fbf0 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> > This requires the linear region to be mapped down to pages,
> > which may adversely affect performance in some cases.
> >
> > +config RODATA_FULL_USE_PTE_CONT
> > + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> > + depends on RODATA_FULL_DEFAULT_ENABLED
> > + default y
> > + help
> > + Apply PTE_CONT on linear mapping as much as we can when
> > + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> > + impaction on performance by small pte granularity.
> > +
> > config ARM64_SW_TTBR0_PAN
> > bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> > help
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index cfd9deb..8017b17 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> > * The following mapping attributes may be updated in live
> > * kernel mappings without the need for break-before-make.
> > */
> > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> > +#else
> > + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> > +#endif
> >
> > /* creating or taking down mappings is always safe */
> > if (old == 0 || new == 0)
> > return true;
> >
> > /* live contiguous mappings may not be manipulated at all */
> > - if ((old | new) & PTE_CONT)
> > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > + if (old | new) & PTE_CONT)
> > return false;
> > +#endif
> >
> > /* Transitioning from Non-Global to Global is unsafe */
> > if (old & ~new & PTE_NG)
> > @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> >
> > /* use a contiguous mapping if the range is suitably aligned */
> > if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> > - (flags & NO_CONT_MAPPINGS) == 0)
> > + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> > __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
> >
> > init_pte(pmdp, addr, next, phys, __prot);
> > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > index a3bacd7..88a87eb 100644
> > --- a/arch/arm64/mm/pageattr.c
> > +++ b/arch/arm64/mm/pageattr.c
> > @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> > if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> > pgprot_val(clear_mask) == PTE_RDONLY)) {
> > for (i = 0; i < area->nr_pages; i++) {
> > +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> > + unsigned long cont_pte_low_bound;
> > + unsigned long addr;
> > +
> > + addr = (u64)page_address(area->pages[i]);
> > + cont_pte_low_bound = addr & CONT_PTE_MASK;
> > + __change_memory_common(cont_pte_low_bound,
> > + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> > +#endif
> > __change_memory_common((u64)page_address(area->pages[i]),
> > PAGE_SIZE, set_mask, clear_mask);
> > }
> > --
> > 1.9.1
> >
On Mon, 22 Nov 2021 at 10:00, Zhaoyang Huang <[email protected]> wrote:
>
> On Mon, Nov 22, 2021 at 4:52 PM Ard Biesheuvel <[email protected]> wrote:
> >
> > On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
> > >
> > > From: Zhaoyang Huang <[email protected]>
> > >
> > > Kernel linear mapping will be split to the smallest granularity when
> > > RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> > > to apply PTE_CONT on pte.
> > >
> > > Signed-off-by: Zhaoyang Huang <[email protected]>
> >
> > How would this lead to TLB pressure, and how does the use of
> > contiguous mappings mitigate that? The linear mapping of the kernel is
> > rarely used, as all normal accesses to it go via the vmalloc region,
> > so in which case would TLB entries be allocated for this region in a
> > way that could cause a measurable performance impact?
> In fact, the patch is about to use PTE_CONT *OUT OF* the range of
> kernel text.
OK, I had missed that, apologies.
> Would you please have a look at the code. It apply
> PTE_CONT during map_mem and then clear it when load_module change the
> corresponding linear mapping to the area it use in vmalloc area.
You cannot change the PTE_CONT attribute on live mappings.
> >
> >
> > > ---
> > > arch/arm64/Kconfig | 9 +++++++++
> > > arch/arm64/mm/mmu.c | 10 ++++++++--
> > > arch/arm64/mm/pageattr.c | 9 +++++++++
> > > 3 files changed, 26 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > index fee914c..3f8fbf0 100644
> > > --- a/arch/arm64/Kconfig
> > > +++ b/arch/arm64/Kconfig
> > > @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> > > This requires the linear region to be mapped down to pages,
> > > which may adversely affect performance in some cases.
> > >
> > > +config RODATA_FULL_USE_PTE_CONT
> > > + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> > > + depends on RODATA_FULL_DEFAULT_ENABLED
> > > + default y
> > > + help
> > > + Apply PTE_CONT on linear mapping as much as we can when
> > > + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> > > + impaction on performance by small pte granularity.
> > > +
> > > config ARM64_SW_TTBR0_PAN
> > > bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> > > help
> > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > index cfd9deb..8017b17 100644
> > > --- a/arch/arm64/mm/mmu.c
> > > +++ b/arch/arm64/mm/mmu.c
> > > @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> > > * The following mapping attributes may be updated in live
> > > * kernel mappings without the need for break-before-make.
> > > */
> > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> > > +#else
> > > + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> > > +#endif
What justifies this change? Why is it ok in certain cases to update
the PTE_CONT attribute without BBM?
> > >
> > > /* creating or taking down mappings is always safe */
> > > if (old == 0 || new == 0)
> > > return true;
> > >
> > > /* live contiguous mappings may not be manipulated at all */
> > > - if ((old | new) & PTE_CONT)
> > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > + if (old | new) & PTE_CONT)
> > > return false;
> > > +#endif
> > >
> > > /* Transitioning from Non-Global to Global is unsafe */
> > > if (old & ~new & PTE_NG)
> > > @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> > >
> > > /* use a contiguous mapping if the range is suitably aligned */
> > > if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> > > - (flags & NO_CONT_MAPPINGS) == 0)
> > > + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> > > __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
> > >
> > > init_pte(pmdp, addr, next, phys, __prot);
> > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > > index a3bacd7..88a87eb 100644
> > > --- a/arch/arm64/mm/pageattr.c
> > > +++ b/arch/arm64/mm/pageattr.c
> > > @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> > > if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> > > pgprot_val(clear_mask) == PTE_RDONLY)) {
> > > for (i = 0; i < area->nr_pages; i++) {
> > > +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > + unsigned long cont_pte_low_bound;
> > > + unsigned long addr;
> > > +
> > > + addr = (u64)page_address(area->pages[i]);
> > > + cont_pte_low_bound = addr & CONT_PTE_MASK;
> > > + __change_memory_common(cont_pte_low_bound,
> > > + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> > > +#endif
> > > __change_memory_common((u64)page_address(area->pages[i]),
> > > PAGE_SIZE, set_mask, clear_mask);
> > > }
> > > --
> > > 1.9.1
> > >
On Mon, Nov 22, 2021 at 5:04 PM Ard Biesheuvel <[email protected]> wrote:
>
> On Mon, 22 Nov 2021 at 10:00, Zhaoyang Huang <[email protected]> wrote:
> >
> > On Mon, Nov 22, 2021 at 4:52 PM Ard Biesheuvel <[email protected]> wrote:
> > >
> > > On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
> > > >
> > > > From: Zhaoyang Huang <[email protected]>
> > > >
> > > > Kernel linear mapping will be split to the smallest granularity when
> > > > RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> > > > to apply PTE_CONT on pte.
> > > >
> > > > Signed-off-by: Zhaoyang Huang <[email protected]>
> > >
> > > How would this lead to TLB pressure, and how does the use of
> > > contiguous mappings mitigate that? The linear mapping of the kernel is
> > > rarely used, as all normal accesses to it go via the vmalloc region,
> > > so in which case would TLB entries be allocated for this region in a
> > > way that could cause a measurable performance impact?
> > In fact, the patch is about to use PTE_CONT *OUT OF* the range of
> > kernel text.
>
> OK, I had missed that, apologies.
>
> > Would you please have a look at the code. It apply
> > PTE_CONT during map_mem and then clear it when load_module change the
> > corresponding linear mapping to the area it use in vmalloc area.
>
> You cannot change the PTE_CONT attribute on live mappings.
Is it an inner constraint from ASIC perspective? PTE_CONT is different
to other attributes?
>
> > >
> > >
> > > > ---
> > > > arch/arm64/Kconfig | 9 +++++++++
> > > > arch/arm64/mm/mmu.c | 10 ++++++++--
> > > > arch/arm64/mm/pageattr.c | 9 +++++++++
> > > > 3 files changed, 26 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > > index fee914c..3f8fbf0 100644
> > > > --- a/arch/arm64/Kconfig
> > > > +++ b/arch/arm64/Kconfig
> > > > @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> > > > This requires the linear region to be mapped down to pages,
> > > > which may adversely affect performance in some cases.
> > > >
> > > > +config RODATA_FULL_USE_PTE_CONT
> > > > + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> > > > + depends on RODATA_FULL_DEFAULT_ENABLED
> > > > + default y
> > > > + help
> > > > + Apply PTE_CONT on linear mapping as much as we can when
> > > > + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> > > > + impaction on performance by small pte granularity.
> > > > +
> > > > config ARM64_SW_TTBR0_PAN
> > > > bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> > > > help
> > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > > index cfd9deb..8017b17 100644
> > > > --- a/arch/arm64/mm/mmu.c
> > > > +++ b/arch/arm64/mm/mmu.c
> > > > @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> > > > * The following mapping attributes may be updated in live
> > > > * kernel mappings without the need for break-before-make.
> > > > */
> > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> > > > +#else
> > > > + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> > > > +#endif
>
> What justifies this change? Why is it ok in certain cases to update
> the PTE_CONT attribute without BBM?
BBM?
I am not sure if it is ok here, but I just find nobody else change
PTE_CONT so far other than this commit.
>
> > > >
> > > > /* creating or taking down mappings is always safe */
> > > > if (old == 0 || new == 0)
> > > > return true;
> > > >
> > > > /* live contiguous mappings may not be manipulated at all */
> > > > - if ((old | new) & PTE_CONT)
> > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > + if ((old | new) & PTE_CONT)
> > > > return false;
> > > > +#endif
> > > >
> > > > /* Transitioning from Non-Global to Global is unsafe */
> > > > if (old & ~new & PTE_NG)
> > > > @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> > > >
> > > > /* use a contiguous mapping if the range is suitably aligned */
> > > > if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> > > > - (flags & NO_CONT_MAPPINGS) == 0)
> > > > + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> > > > __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
> > > >
> > > > init_pte(pmdp, addr, next, phys, __prot);
> > > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > > > index a3bacd7..88a87eb 100644
> > > > --- a/arch/arm64/mm/pageattr.c
> > > > +++ b/arch/arm64/mm/pageattr.c
> > > > @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> > > > if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> > > > pgprot_val(clear_mask) == PTE_RDONLY)) {
> > > > for (i = 0; i < area->nr_pages; i++) {
> > > > +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > + unsigned long cont_pte_low_bound;
> > > > + unsigned long addr;
> > > > +
> > > > + addr = (u64)page_address(area->pages[i]);
> > > > + cont_pte_low_bound = addr & CONT_PTE_MASK;
> > > > + __change_memory_common(cont_pte_low_bound,
> > > > + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> > > > +#endif
> > > > __change_memory_common((u64)page_address(area->pages[i]),
> > > > PAGE_SIZE, set_mask, clear_mask);
> > > > }
> > > > --
> > > > 1.9.1
> > > >
On Mon, 22 Nov 2021 at 10:17, Zhaoyang Huang <[email protected]> wrote:
>
> On Mon, Nov 22, 2021 at 5:04 PM Ard Biesheuvel <[email protected]> wrote:
> >
> > On Mon, 22 Nov 2021 at 10:00, Zhaoyang Huang <[email protected]> wrote:
> > >
> > > On Mon, Nov 22, 2021 at 4:52 PM Ard Biesheuvel <[email protected]> wrote:
> > > >
> > > > On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
> > > > >
> > > > > From: Zhaoyang Huang <[email protected]>
> > > > >
> > > > > Kernel linear mapping will be split to the smallest granularity when
> > > > > RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> > > > > to apply PTE_CONT on pte.
> > > > >
> > > > > Signed-off-by: Zhaoyang Huang <[email protected]>
> > > >
> > > > How would this lead to TLB pressure, and how does the use of
> > > > contiguous mappings mitigate that? The linear mapping of the kernel is
> > > > rarely used, as all normal accesses to it go via the vmalloc region,
> > > > so in which case would TLB entries be allocated for this region in a
> > > > way that could cause a measurable performance impact?
> > > In fact, the patch is about to use PTE_CONT *OUT OF* the range of
> > > kernel text.
> >
> > OK, I had missed that, apologies.
> >
> > > Would you please have a look at the code. It apply
> > > PTE_CONT during map_mem and then clear it when load_module change the
> > > corresponding linear mapping to the area it use in vmalloc area.
> >
> > You cannot change the PTE_CONT attribute on live mappings.
> Is it an inner constraint from ASIC perspective? PTE_CONT is different
> to other attributes?
The PTE_CONT attributes on live translation entries must always be in
sync in all entries covering the same contiguous group, or you might
cause TLB conflict aborts.
> >
> > > >
> > > >
> > > > > ---
> > > > > arch/arm64/Kconfig | 9 +++++++++
> > > > > arch/arm64/mm/mmu.c | 10 ++++++++--
> > > > > arch/arm64/mm/pageattr.c | 9 +++++++++
> > > > > 3 files changed, 26 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > > > index fee914c..3f8fbf0 100644
> > > > > --- a/arch/arm64/Kconfig
> > > > > +++ b/arch/arm64/Kconfig
> > > > > @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> > > > > This requires the linear region to be mapped down to pages,
> > > > > which may adversely affect performance in some cases.
> > > > >
> > > > > +config RODATA_FULL_USE_PTE_CONT
> > > > > + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> > > > > + depends on RODATA_FULL_DEFAULT_ENABLED
> > > > > + default y
> > > > > + help
> > > > > + Apply PTE_CONT on linear mapping as much as we can when
> > > > > + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> > > > > + impaction on performance by small pte granularity.
> > > > > +
> > > > > config ARM64_SW_TTBR0_PAN
> > > > > bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> > > > > help
> > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > > > index cfd9deb..8017b17 100644
> > > > > --- a/arch/arm64/mm/mmu.c
> > > > > +++ b/arch/arm64/mm/mmu.c
> > > > > @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> > > > > * The following mapping attributes may be updated in live
> > > > > * kernel mappings without the need for break-before-make.
> > > > > */
> > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> > > > > +#else
> > > > > + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> > > > > +#endif
> >
> > What justifies this change? Why is it ok in certain cases to update
> > the PTE_CONT attribute without BBM?
> BBM?
> I am not sure if it is ok here, but I just find nobody else change
> PTE_CONT so far other than this commit.
No it is not ok. BBM == break before make, which means you need to
install invalid entries for the entire contiguous group before you can
change the PTE_CONT attributes. As other CPUs may be accessing the
same region, there is no safe way to do this, which is why we don't
permit PTE_CONT to be changed at all.
> >
> > > > >
> > > > > /* creating or taking down mappings is always safe */
> > > > > if (old == 0 || new == 0)
> > > > > return true;
> > > > >
> > > > > /* live contiguous mappings may not be manipulated at all */
> > > > > - if ((old | new) & PTE_CONT)
> > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > + if ((old | new) & PTE_CONT)
> > > > > return false;
> > > > > +#endif
> > > > >
> > > > > /* Transitioning from Non-Global to Global is unsafe */
> > > > > if (old & ~new & PTE_NG)
> > > > > @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> > > > >
> > > > > /* use a contiguous mapping if the range is suitably aligned */
> > > > > if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> > > > > - (flags & NO_CONT_MAPPINGS) == 0)
> > > > > + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> > > > > __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
> > > > >
> > > > > init_pte(pmdp, addr, next, phys, __prot);
> > > > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > > > > index a3bacd7..88a87eb 100644
> > > > > --- a/arch/arm64/mm/pageattr.c
> > > > > +++ b/arch/arm64/mm/pageattr.c
> > > > > @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> > > > > if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> > > > > pgprot_val(clear_mask) == PTE_RDONLY)) {
> > > > > for (i = 0; i < area->nr_pages; i++) {
> > > > > +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > + unsigned long cont_pte_low_bound;
> > > > > + unsigned long addr;
> > > > > +
> > > > > + addr = (u64)page_address(area->pages[i]);
> > > > > + cont_pte_low_bound = addr & CONT_PTE_MASK;
> > > > > + __change_memory_common(cont_pte_low_bound,
> > > > > + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> > > > > +#endif
> > > > > __change_memory_common((u64)page_address(area->pages[i]),
> > > > > PAGE_SIZE, set_mask, clear_mask);
> > > > > }
> > > > > --
> > > > > 1.9.1
> > > > >
On Mon, Nov 22, 2021 at 5:23 PM Ard Biesheuvel <[email protected]> wrote:
>
> On Mon, 22 Nov 2021 at 10:17, Zhaoyang Huang <[email protected]> wrote:
> >
> > On Mon, Nov 22, 2021 at 5:04 PM Ard Biesheuvel <[email protected]> wrote:
> > >
> > > On Mon, 22 Nov 2021 at 10:00, Zhaoyang Huang <[email protected]> wrote:
> > > >
> > > > On Mon, Nov 22, 2021 at 4:52 PM Ard Biesheuvel <[email protected]> wrote:
> > > > >
> > > > > On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
> > > > > >
> > > > > > From: Zhaoyang Huang <[email protected]>
> > > > > >
> > > > > > Kernel linear mapping will be split to the smallest granularity when
> > > > > > RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> > > > > > to apply PTE_CONT on pte.
> > > > > >
> > > > > > Signed-off-by: Zhaoyang Huang <[email protected]>
> > > > >
> > > > > How would this lead to TLB pressure, and how does the use of
> > > > > contiguous mappings mitigate that? The linear mapping of the kernel is
> > > > > rarely used, as all normal accesses to it go via the vmalloc region,
> > > > > so in which case would TLB entries be allocated for this region in a
> > > > > way that could cause a measurable performance impact?
> > > > In fact, the patch is about to use PTE_CONT *OUT OF* the range of
> > > > kernel text.
> > >
> > > OK, I had missed that, apologies.
> > >
> > > > Would you please have a look at the code. It apply
> > > > PTE_CONT during map_mem and then clear it when load_module change the
> > > > corresponding linear mapping to the area it use in vmalloc area.
> > >
> > > You cannot change the PTE_CONT attribute on live mappings.
> > Is it an inner constraint from ASIC perspective? PTE_CONT is different
> > to other attributes?
>
> The PTE_CONT attributes on live translation entries must always be in
> sync in all entries covering the same contiguous group, or you might
> cause TLB conflict aborts.
>
> > >
> > > > >
> > > > >
> > > > > > ---
> > > > > > arch/arm64/Kconfig | 9 +++++++++
> > > > > > arch/arm64/mm/mmu.c | 10 ++++++++--
> > > > > > arch/arm64/mm/pageattr.c | 9 +++++++++
> > > > > > 3 files changed, 26 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > > > > index fee914c..3f8fbf0 100644
> > > > > > --- a/arch/arm64/Kconfig
> > > > > > +++ b/arch/arm64/Kconfig
> > > > > > @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> > > > > > This requires the linear region to be mapped down to pages,
> > > > > > which may adversely affect performance in some cases.
> > > > > >
> > > > > > +config RODATA_FULL_USE_PTE_CONT
> > > > > > + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> > > > > > + depends on RODATA_FULL_DEFAULT_ENABLED
> > > > > > + default y
> > > > > > + help
> > > > > > + Apply PTE_CONT on linear mapping as much as we can when
> > > > > > + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> > > > > > + impaction on performance by small pte granularity.
> > > > > > +
> > > > > > config ARM64_SW_TTBR0_PAN
> > > > > > bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> > > > > > help
> > > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > > > > index cfd9deb..8017b17 100644
> > > > > > --- a/arch/arm64/mm/mmu.c
> > > > > > +++ b/arch/arm64/mm/mmu.c
> > > > > > @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> > > > > > * The following mapping attributes may be updated in live
> > > > > > * kernel mappings without the need for break-before-make.
> > > > > > */
> > > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> > > > > > +#else
> > > > > > + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> > > > > > +#endif
> > >
> > > What justifies this change? Why is it ok in certain cases to update
> > > the PTE_CONT attribute without BBM?
> > BBM?
> > I am not sure if it is ok here, but I just find nobody else change
> > PTE_CONT so far other than this commit.
>
> No it is not ok. BBM == break before make, which means you need to
> install invalid entries for the entire contiguous group before you can
> change the PTE_CONT attributes. As other CPUs may be accessing the
> same region, there is no safe way to do this, which is why we don't
> permit PTE_CONT to be changed at all.
ok, got it. But from practical scenario perspective, could we assume
that the corresponding linear map of the vmalloc area would NOT be
accessed at all. If it does so, could we just clear PTE_VALID on the
linear pte and leave PTE_CONT on the others' pte within the same
region. The linear mapping could be reestablished when vmalloc_free.
>
>
> > >
> > > > > >
> > > > > > /* creating or taking down mappings is always safe */
> > > > > > if (old == 0 || new == 0)
> > > > > > return true;
> > > > > >
> > > > > > /* live contiguous mappings may not be manipulated at all */
> > > > > > - if ((old | new) & PTE_CONT)
> > > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > + if ((old | new) & PTE_CONT)
> > > > > > return false;
> > > > > > +#endif
> > > > > >
> > > > > > /* Transitioning from Non-Global to Global is unsafe */
> > > > > > if (old & ~new & PTE_NG)
> > > > > > @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> > > > > >
> > > > > > /* use a contiguous mapping if the range is suitably aligned */
> > > > > > if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> > > > > > - (flags & NO_CONT_MAPPINGS) == 0)
> > > > > > + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> > > > > > __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
> > > > > >
> > > > > > init_pte(pmdp, addr, next, phys, __prot);
> > > > > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > > > > > index a3bacd7..88a87eb 100644
> > > > > > --- a/arch/arm64/mm/pageattr.c
> > > > > > +++ b/arch/arm64/mm/pageattr.c
> > > > > > @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> > > > > > if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> > > > > > pgprot_val(clear_mask) == PTE_RDONLY)) {
> > > > > > for (i = 0; i < area->nr_pages; i++) {
> > > > > > +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > + unsigned long cont_pte_low_bound;
> > > > > > + unsigned long addr;
> > > > > > +
> > > > > > + addr = (u64)page_address(area->pages[i]);
> > > > > > + cont_pte_low_bound = addr & CONT_PTE_MASK;
> > > > > > + __change_memory_common(cont_pte_low_bound,
> > > > > > + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> > > > > > +#endif
> > > > > > __change_memory_common((u64)page_address(area->pages[i]),
> > > > > > PAGE_SIZE, set_mask, clear_mask);
> > > > > > }
> > > > > > --
> > > > > > 1.9.1
> > > > > >
On Mon, 22 Nov 2021 at 12:25, Zhaoyang Huang <[email protected]> wrote:
>
> On Mon, Nov 22, 2021 at 5:23 PM Ard Biesheuvel <[email protected]> wrote:
> >
> > On Mon, 22 Nov 2021 at 10:17, Zhaoyang Huang <[email protected]> wrote:
> > >
> > > On Mon, Nov 22, 2021 at 5:04 PM Ard Biesheuvel <[email protected]> wrote:
> > > >
> > > > On Mon, 22 Nov 2021 at 10:00, Zhaoyang Huang <[email protected]> wrote:
> > > > >
> > > > > On Mon, Nov 22, 2021 at 4:52 PM Ard Biesheuvel <[email protected]> wrote:
> > > > > >
> > > > > > On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
> > > > > > >
> > > > > > > From: Zhaoyang Huang <[email protected]>
> > > > > > >
> > > > > > > Kernel linear mapping will be split to the smallest granularity when
> > > > > > > RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> > > > > > > to apply PTE_CONT on pte.
> > > > > > >
> > > > > > > Signed-off-by: Zhaoyang Huang <[email protected]>
> > > > > >
> > > > > > How would this lead to TLB pressure, and how does the use of
> > > > > > contiguous mappings mitigate that? The linear mapping of the kernel is
> > > > > > rarely used, as all normal accesses to it go via the vmalloc region,
> > > > > > so in which case would TLB entries be allocated for this region in a
> > > > > > way that could cause a measurable performance impact?
> > > > > In fact, the patch is about to use PTE_CONT *OUT OF* the range of
> > > > > kernel text.
> > > >
> > > > OK, I had missed that, apologies.
> > > >
> > > > > Would you please have a look at the code. It apply
> > > > > PTE_CONT during map_mem and then clear it when load_module change the
> > > > > corresponding linear mapping to the area it use in vmalloc area.
> > > >
> > > > You cannot change the PTE_CONT attribute on live mappings.
> > > Is it an inner constraint from ASIC perspective? PTE_CONT is different
> > > to other attributes?
> >
> > The PTE_CONT attributes on live translation entries must always be in
> > sync in all entries covering the same contiguous group, or you might
> > cause TLB conflict aborts.
> >
> > > >
> > > > > >
> > > > > >
> > > > > > > ---
> > > > > > > arch/arm64/Kconfig | 9 +++++++++
> > > > > > > arch/arm64/mm/mmu.c | 10 ++++++++--
> > > > > > > arch/arm64/mm/pageattr.c | 9 +++++++++
> > > > > > > 3 files changed, 26 insertions(+), 2 deletions(-)
> > > > > > >
> > > > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > > > > > index fee914c..3f8fbf0 100644
> > > > > > > --- a/arch/arm64/Kconfig
> > > > > > > +++ b/arch/arm64/Kconfig
> > > > > > > @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> > > > > > > This requires the linear region to be mapped down to pages,
> > > > > > > which may adversely affect performance in some cases.
> > > > > > >
> > > > > > > +config RODATA_FULL_USE_PTE_CONT
> > > > > > > + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> > > > > > > + depends on RODATA_FULL_DEFAULT_ENABLED
> > > > > > > + default y
> > > > > > > + help
> > > > > > > + Apply PTE_CONT on linear mapping as much as we can when
> > > > > > > + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> > > > > > > + impaction on performance by small pte granularity.
> > > > > > > +
> > > > > > > config ARM64_SW_TTBR0_PAN
> > > > > > > bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> > > > > > > help
> > > > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > > > > > index cfd9deb..8017b17 100644
> > > > > > > --- a/arch/arm64/mm/mmu.c
> > > > > > > +++ b/arch/arm64/mm/mmu.c
> > > > > > > @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> > > > > > > * The following mapping attributes may be updated in live
> > > > > > > * kernel mappings without the need for break-before-make.
> > > > > > > */
> > > > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > > pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> > > > > > > +#else
> > > > > > > + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> > > > > > > +#endif
> > > >
> > > > What justifies this change? Why is it ok in certain cases to update
> > > > the PTE_CONT attribute without BBM?
> > > BBM?
> > > I am not sure if it is ok here, but I just find nobody else change
> > > PTE_CONT so far other than this commit.
> >
> > No it is not ok. BBM == break before make, which means you need to
> > install invalid entries for the entire contiguous group before you can
> > change the PTE_CONT attributes. As other CPUs may be accessing the
> > same region, there is no safe way to do this, which is why we don't
> > permit PTE_CONT to be changed at all.
> ok, got it. But from practical scenario perspective, could we assume
> that the corresponding linear map of the vmalloc area would NOT be
> accessed at all.
> If it does so, could we just clear PTE_VALID on the
> linear pte and leave PTE_CONT on the others' pte within the same
> region. The linear mapping could be reestablished when vmalloc_free.
No. Such an invalid entry would conflict with the other PTE_CONT ones
in the same contiguous group.
> >
> >
> > > >
> > > > > > >
> > > > > > > /* creating or taking down mappings is always safe */
> > > > > > > if (old == 0 || new == 0)
> > > > > > > return true;
> > > > > > >
> > > > > > > /* live contiguous mappings may not be manipulated at all */
> > > > > > > - if ((old | new) & PTE_CONT)
> > > > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > > + if ((old | new) & PTE_CONT)
> > > > > > > return false;
> > > > > > > +#endif
> > > > > > >
> > > > > > > /* Transitioning from Non-Global to Global is unsafe */
> > > > > > > if (old & ~new & PTE_NG)
> > > > > > > @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> > > > > > >
> > > > > > > /* use a contiguous mapping if the range is suitably aligned */
> > > > > > > if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> > > > > > > - (flags & NO_CONT_MAPPINGS) == 0)
> > > > > > > + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> > > > > > > __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
> > > > > > >
> > > > > > > init_pte(pmdp, addr, next, phys, __prot);
> > > > > > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > > > > > > index a3bacd7..88a87eb 100644
> > > > > > > --- a/arch/arm64/mm/pageattr.c
> > > > > > > +++ b/arch/arm64/mm/pageattr.c
> > > > > > > @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> > > > > > > if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> > > > > > > pgprot_val(clear_mask) == PTE_RDONLY)) {
> > > > > > > for (i = 0; i < area->nr_pages; i++) {
> > > > > > > +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > > + unsigned long cont_pte_low_bound;
> > > > > > > + unsigned long addr;
> > > > > > > +
> > > > > > > + addr = (u64)page_address(area->pages[i]);
> > > > > > > + cont_pte_low_bound = addr & CONT_PTE_MASK;
> > > > > > > + __change_memory_common(cont_pte_low_bound,
> > > > > > > + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> > > > > > > +#endif
> > > > > > > __change_memory_common((u64)page_address(area->pages[i]),
> > > > > > > PAGE_SIZE, set_mask, clear_mask);
> > > > > > > }
> > > > > > > --
> > > > > > > 1.9.1
> > > > > > >
ok. Could the following change be helpful? I think it is safe as
nobody else but the allocator be aware of this memory block and will
keep the attributes integrated while keeping the pages.
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index c50664b5b72c..0a9da8295d53 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -236,3 +236,45 @@ bool kernel_page_present(struct page *page)
ptep = pte_offset_kernel(pmdp, addr);
return pte_valid(READ_ONCE(*ptep));
}
+
+void arch_alloc_page(struct page *page, int order)
+{
+ unsigned long addr;
+ unsigned long cont_pte_low_bound;
+
+ if (!rodata_full)
+ return;
+ addr = (u64)page_address(page);
+ if ((order >= 4) && (addr & ~CONT_PTE_MASK) == 0) {
+ order -= 4;
+ do {
+ cont_pte_low_bound = addr & CONT_PTE_MASK;
+ __change_memory_common(cont_pte_low_bound,
+ (~CONT_PTE_MASK + 1),
__pgprot(PTE_CONT), __pgprot(0));
+ addr = (u64)page_address(page);
+ page += 4;
+ order--;
+ }while (order >= 0);
+ }
+}
+
+void arch_free_page(struct page *page, int order)
+{
+ unsigned long addr;
+ unsigned long cont_pte_low_bound;
+
+ if (!rodata_full)
+ return;
+ addr = (u64)page_address(page);
+ if ((order >= 4) && (addr & ~CONT_PTE_MASK) == 0) {
+ order -= 4;
+ do {
+ cont_pte_low_bound = addr & CONT_PTE_MASK;
+ __change_memory_common(cont_pte_low_bound,
+ (~CONT_PTE_MASK + 1),
__pgprot(0), __pgprot(PTE_CONT));
+ addr = (u64)page_address(page);
+ page += 4;
+ order--;
+ }while (order >= 0);
+ }
+}
On Tue, Nov 23, 2021 at 2:16 AM Ard Biesheuvel <[email protected]> wrote:
>
> On Mon, 22 Nov 2021 at 12:25, Zhaoyang Huang <[email protected]> wrote:
> >
> > On Mon, Nov 22, 2021 at 5:23 PM Ard Biesheuvel <[email protected]> wrote:
> > >
> > > On Mon, 22 Nov 2021 at 10:17, Zhaoyang Huang <[email protected]> wrote:
> > > >
> > > > On Mon, Nov 22, 2021 at 5:04 PM Ard Biesheuvel <[email protected]> wrote:
> > > > >
> > > > > On Mon, 22 Nov 2021 at 10:00, Zhaoyang Huang <[email protected]> wrote:
> > > > > >
> > > > > > On Mon, Nov 22, 2021 at 4:52 PM Ard Biesheuvel <[email protected]> wrote:
> > > > > > >
> > > > > > > On Mon, 22 Nov 2021 at 06:29, Huangzhaoyang <[email protected]> wrote:
> > > > > > > >
> > > > > > > > From: Zhaoyang Huang <[email protected]>
> > > > > > > >
> > > > > > > > Kernel linear mapping will be split to the smallest granularity when
> > > > > > > > RODATA_FULL applied, which could lead to TLB pressure. Introduce a method
> > > > > > > > to apply PTE_CONT on pte.
> > > > > > > >
> > > > > > > > Signed-off-by: Zhaoyang Huang <[email protected]>
> > > > > > >
> > > > > > > How would this lead to TLB pressure, and how does the use of
> > > > > > > contiguous mappings mitigate that? The linear mapping of the kernel is
> > > > > > > rarely used, as all normal accesses to it go via the vmalloc region,
> > > > > > > so in which case would TLB entries be allocated for this region in a
> > > > > > > way that could cause a measurable performance impact?
> > > > > > In fact, the patch is about to use PTE_CONT *OUT OF* the range of
> > > > > > kernel text.
> > > > >
> > > > > OK, I had missed that, apologies.
> > > > >
> > > > > > Would you please have a look at the code. It apply
> > > > > > PTE_CONT during map_mem and then clear it when load_module change the
> > > > > > corresponding linear mapping to the area it use in vmalloc area.
> > > > >
> > > > > You cannot change the PTE_CONT attribute on live mappings.
> > > > Is it an inner constraint from ASIC perspective? PTE_CONT is different
> > > > to other attributes?
> > >
> > > The PTE_CONT attributes on live translation entries must always be in
> > > sync in all entries covering the same contiguous group, or you might
> > > cause TLB conflict aborts.
> > >
> > > > >
> > > > > > >
> > > > > > >
> > > > > > > > ---
> > > > > > > > arch/arm64/Kconfig | 9 +++++++++
> > > > > > > > arch/arm64/mm/mmu.c | 10 ++++++++--
> > > > > > > > arch/arm64/mm/pageattr.c | 9 +++++++++
> > > > > > > > 3 files changed, 26 insertions(+), 2 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > > > > > > index fee914c..3f8fbf0 100644
> > > > > > > > --- a/arch/arm64/Kconfig
> > > > > > > > +++ b/arch/arm64/Kconfig
> > > > > > > > @@ -1198,6 +1198,15 @@ config RODATA_FULL_DEFAULT_ENABLED
> > > > > > > > This requires the linear region to be mapped down to pages,
> > > > > > > > which may adversely affect performance in some cases.
> > > > > > > >
> > > > > > > > +config RODATA_FULL_USE_PTE_CONT
> > > > > > > > + bool "Apply PTE_CONT when RODATA_FULL_DEFAULT_ENABLED enabled"
> > > > > > > > + depends on RODATA_FULL_DEFAULT_ENABLED
> > > > > > > > + default y
> > > > > > > > + help
> > > > > > > > + Apply PTE_CONT on linear mapping as much as we can when
> > > > > > > > + RODATA_FULL_DEFAULT_ENABLED enabled which could decrease the
> > > > > > > > + impaction on performance by small pte granularity.
> > > > > > > > +
> > > > > > > > config ARM64_SW_TTBR0_PAN
> > > > > > > > bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
> > > > > > > > help
> > > > > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > > > > > > index cfd9deb..8017b17 100644
> > > > > > > > --- a/arch/arm64/mm/mmu.c
> > > > > > > > +++ b/arch/arm64/mm/mmu.c
> > > > > > > > @@ -124,15 +124,21 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> > > > > > > > * The following mapping attributes may be updated in live
> > > > > > > > * kernel mappings without the need for break-before-make.
> > > > > > > > */
> > > > > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > > > pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> > > > > > > > +#else
> > > > > > > > + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG | PTE_CONT;
> > > > > > > > +#endif
> > > > >
> > > > > What justifies this change? Why is it ok in certain cases to update
> > > > > the PTE_CONT attribute without BBM?
> > > > BBM?
> > > > I am not sure if it is ok here, but I just find nobody else change
> > > > PTE_CONT so far other than this commit.
> > >
> > > No it is not ok. BBM == break before make, which means you need to
> > > install invalid entries for the entire contiguous group before you can
> > > change the PTE_CONT attributes. As other CPUs may be accessing the
> > > same region, there is no safe way to do this, which is why we don't
> > > permit PTE_CONT to be changed at all.
> > ok, got it. But from practical scenario perspective, could we assume
> > that the corresponding linear map of the vmalloc area would NOT be
> > accessed at all.
> > If it does so, could we just clear PTE_VALID on the
> > linear pte and leave PTE_CONT on the others' pte within the same
> > region. The linear mapping could be reestablished when vmalloc_free.
>
> No. Such an invalid entry would conflict with the other PTE_CONT ones
> in the same contiguous group.
>
>
> > >
> > >
> > > > >
> > > > > > > >
> > > > > > > > /* creating or taking down mappings is always safe */
> > > > > > > > if (old == 0 || new == 0)
> > > > > > > > return true;
> > > > > > > >
> > > > > > > > /* live contiguous mappings may not be manipulated at all */
> > > > > > > > - if ((old | new) & PTE_CONT)
> > > > > > > > +#ifndef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > > > + if ((old | new) & PTE_CONT)
> > > > > > > > return false;
> > > > > > > > +#endif
> > > > > > > >
> > > > > > > > /* Transitioning from Non-Global to Global is unsafe */
> > > > > > > > if (old & ~new & PTE_NG)
> > > > > > > > @@ -206,7 +212,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> > > > > > > >
> > > > > > > > /* use a contiguous mapping if the range is suitably aligned */
> > > > > > > > if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
> > > > > > > > - (flags & NO_CONT_MAPPINGS) == 0)
> > > > > > > > + (IS_ENABLED(CONFIG_RODATA_FULL_USE_PTE_CONT) || (flags & NO_CONT_MAPPINGS) == 0))
> > > > > > > > __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
> > > > > > > >
> > > > > > > > init_pte(pmdp, addr, next, phys, __prot);
> > > > > > > > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > > > > > > > index a3bacd7..88a87eb 100644
> > > > > > > > --- a/arch/arm64/mm/pageattr.c
> > > > > > > > +++ b/arch/arm64/mm/pageattr.c
> > > > > > > > @@ -99,6 +99,15 @@ static int change_memory_common(unsigned long addr, int numpages,
> > > > > > > > if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> > > > > > > > pgprot_val(clear_mask) == PTE_RDONLY)) {
> > > > > > > > for (i = 0; i < area->nr_pages; i++) {
> > > > > > > > +#ifdef CONFIG_RODATA_FULL_USE_PTE_CONT
> > > > > > > > + unsigned long cont_pte_low_bound;
> > > > > > > > + unsigned long addr;
> > > > > > > > +
> > > > > > > > + addr = (u64)page_address(area->pages[i]);
> > > > > > > > + cont_pte_low_bound = addr & CONT_PTE_MASK;
> > > > > > > > + __change_memory_common(cont_pte_low_bound,
> > > > > > > > + (~CONT_PTE_MASK + 1), __pgprot(0) , __pgprot(PTE_CONT));
> > > > > > > > +#endif
> > > > > > > > __change_memory_common((u64)page_address(area->pages[i]),
> > > > > > > > PAGE_SIZE, set_mask, clear_mask);
> > > > > > > > }
> > > > > > > > --
> > > > > > > > 1.9.1
> > > > > > > >