2023-12-21 15:47:32

by Guo Ren

Subject: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure

From: Guo Ren <[email protected]>

In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
segment fault. Sometimes, it would cause boot failure when the whole
rootfs is rv32.

Freeing unused kernel image (initmem) memory: 2236K
Run /sbin/init as init process
Starting init: /sbin/init exists but couldn't execute it (error -14)
Run /etc/init as init process
...

Cc: [email protected]
Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
Signed-off-by: Guo Ren <[email protected]>
Signed-off-by: Guo Ren <[email protected]>
---
arch/riscv/include/asm/pgtable.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index ab00235b018f..74ffb2178f54 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
#define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)

#ifdef CONFIG_COMPAT
-#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
+#define TASK_SIZE_32 (_AC(0x80000000, UL))
#define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)
#else
--
2.40.1

2023-12-22 01:51:37

by Leonardo Bras

Subject: Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure

Hello Guo Ren,

On Thu, Dec 21, 2023 at 10:46:58AM -0500, [email protected] wrote:
> From: Guo Ren <[email protected]>
>
> In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
> 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
> segment fault. Sometimes, it would cause boot failure when the whole
> rootfs is rv32.

Checking if I get the scenario:

In pgtable.h:
#ifdef CONFIG_64BIT
#define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
#define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)

#ifdef CONFIG_COMPAT
#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
#define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)
#else
[...]

Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in
compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.

from processor.h:
#ifdef CONFIG_64BIT
#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
#define STACK_TOP_MAX TASK_SIZE_64
[...]
#define STACK_TOP DEFAULT_MAP_WINDOW


where:
#define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
with MMAP_VA_BITS_64 being either 48 or 37.

In compat mode,
STACK_TOP = 1 << (32 - 1) -> 0x80000000
TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000

IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.

Then why not:
#ifdef CONFIG_COMPAT
#define TASK_SIZE_32 STACK_TOP

With some comments explaining why there is no need to reserve a PAGE_SIZE
in the TASK_SIZE_32.

Does that make sense?

Thanks!
Leo

>
> Freeing unused kernel image (initmem) memory: 2236K
> Run /sbin/init as init process
> Starting init: /sbin/init exists but couldn't execute it (error -14)
> Run /etc/init as init process
> ...
>
> Cc: [email protected]
> Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> Signed-off-by: Guo Ren <[email protected]>
> Signed-off-by: Guo Ren <[email protected]>
> ---
> arch/riscv/include/asm/pgtable.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index ab00235b018f..74ffb2178f54 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
>
> #ifdef CONFIG_COMPAT
> -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> +#define TASK_SIZE_32 (_AC(0x80000000, UL))




> #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> TASK_SIZE_32 : TASK_SIZE_64)
> #else
> --
> 2.40.1
>

2023-12-22 02:57:40

by Guo Ren

Subject: Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure

On Fri, Dec 22, 2023 at 9:51 AM Leonardo Bras <[email protected]> wrote:
>
> Hello Guo Ren,
>
> On Thu, Dec 21, 2023 at 10:46:58AM -0500, [email protected] wrote:
> > From: Guo Ren <[email protected]>
> >
> > In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
> > 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
> > segment fault. Sometimes, it would cause boot failure when the whole
> > rootfs is rv32.
>
> Checking if I get the scenario:
>
> In pgtable.h:
> #ifdef CONFIG_64BIT
> #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
> #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
>
> #ifdef CONFIG_COMPAT
> #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> TASK_SIZE_32 : TASK_SIZE_64)
> #else
> [...]
>
> Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in
> compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.
>
> from processor.h:
> #ifdef CONFIG_64BIT
> #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
> #define STACK_TOP_MAX TASK_SIZE_64
> [...]
> #define STACK_TOP DEFAULT_MAP_WINDOW
>
>
> where:
> #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
> with MMAP_VA_BITS_64 being either 48 or 37.
>
> In compat mode,
> STACK_TOP = 1 << (32 - 1) -> 0x80000000
> TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000
>
> IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.
Yes, it causes the problem, which causes the boot to fail.

>
> Then why not:
> #ifdef CONFIG_COMPAT
> #define TASK_SIZE_32 STACK_TOP
Yes, it's the solution that I think at first. But I didn't find any
problem with 0x7ffff000 ~ 0x80000000, and then I removed this gap to
unify it with Sv39 and Sv48.

>
> With some comments explaining why there is no need to reserve a PAGE_SIZE
> in the TASK_SIZE_32.
At first, I wanted to put a invalid page between the user & kernel
space, but it seems useless.

>
> Does that make sense?
>
> Thanks!
> Leo
>
> >
> > Freeing unused kernel image (initmem) memory: 2236K
> > Run /sbin/init as init process
> > Starting init: /sbin/init exists but couldn't execute it (error -14)
> > Run /etc/init as init process
> > ...
> >
> > Cc: [email protected]
> > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> > Signed-off-by: Guo Ren <[email protected]>
> > Signed-off-by: Guo Ren <[email protected]>
> > ---
> > arch/riscv/include/asm/pgtable.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index ab00235b018f..74ffb2178f54 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> >
> > #ifdef CONFIG_COMPAT
> > -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > +#define TASK_SIZE_32 (_AC(0x80000000, UL))
>
>
>
>
> > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > TASK_SIZE_32 : TASK_SIZE_64)
> > #else
> > --
> > 2.40.1
> >
>


--
Best Regards
Guo Ren

2023-12-22 03:50:42

by Charlie Jenkins

Subject: Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure

On Fri, Dec 22, 2023 at 10:57:16AM +0800, Guo Ren wrote:
> On Fri, Dec 22, 2023 at 9:51 AM Leonardo Bras <[email protected]> wrote:
> >
> > Hello Guo Ren,
> >
> > On Thu, Dec 21, 2023 at 10:46:58AM -0500, [email protected] wrote:
> > > From: Guo Ren <[email protected]>
> > >
> > > In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
> > > 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
> > > segment fault. Sometimes, it would cause boot failure when the whole
> > > rootfs is rv32.
> >
> > Checking if I get the scenario:
> >
> > In pgtable.h:
> > #ifdef CONFIG_64BIT
> > #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
> > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> >
> > #ifdef CONFIG_COMPAT
> > #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > TASK_SIZE_32 : TASK_SIZE_64)
> > #else
> > [...]
> >
> > Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in
> > compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.
> >
> > from processor.h:
> > #ifdef CONFIG_64BIT
> > #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
> > #define STACK_TOP_MAX TASK_SIZE_64
> > [...]
> > #define STACK_TOP DEFAULT_MAP_WINDOW
> >
> >
> > where:
> > #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
> > with MMAP_VA_BITS_64 being either 48 or 37.
> >
> > In compat mode,
> > STACK_TOP = 1 << (32 - 1) -> 0x80000000
> > TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000
> >
> > IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.
> Yes, it causes the problem, which causes the boot to fail.

I think what Leonardo is getting at is that it is odd that it would
cause boot issues if TASK_SIZE is not equal STACK_TOP. This seems
indicative of a different problem. While this may fix the issue, it
should be valid for TASK_SIZE to be less than STACK_TOP.

- Charlie

>
> >
> > Then why not:
> > #ifdef CONFIG_COMPAT
> > #define TASK_SIZE_32 STACK_TOP
> Yes, it's the solution that I think at first. But I didn't find any
> problem with 0x7ffff000 ~ 0x80000000, and then I removed this gap to
> unify it with Sv39 and Sv48.
>
> >
> > With some comments explaining why there is no need to reserve a PAGE_SIZE
> > in the TASK_SIZE_32.
> At first, I wanted to put a invalid page between the user & kernel
> space, but it seems useless.
>
> >
> > Does that make sense?
> >
> > Thanks!
> > Leo
> >
> > >
> > > Freeing unused kernel image (initmem) memory: 2236K
> > > Run /sbin/init as init process
> > > Starting init: /sbin/init exists but couldn't execute it (error -14)
> > > Run /etc/init as init process
> > > ...
> > >
> > > Cc: [email protected]
> > > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> > > Signed-off-by: Guo Ren <[email protected]>
> > > Signed-off-by: Guo Ren <[email protected]>
> > > ---
> > > arch/riscv/include/asm/pgtable.h | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > > index ab00235b018f..74ffb2178f54 100644
> > > --- a/arch/riscv/include/asm/pgtable.h
> > > +++ b/arch/riscv/include/asm/pgtable.h
> > > @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> > > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> > >
> > > #ifdef CONFIG_COMPAT
> > > -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > > +#define TASK_SIZE_32 (_AC(0x80000000, UL))
> >
> >
> >
> >
> > > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > > TASK_SIZE_32 : TASK_SIZE_64)
> > > #else
> > > --
> > > 2.40.1
> > >
> >
>
>
> --
> Best Regards
> Guo Ren

2023-12-22 04:33:28

by Leonardo Bras

Subject: Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure

On Thu, Dec 21, 2023 at 07:50:27PM -0800, Charlie Jenkins wrote:
> On Fri, Dec 22, 2023 at 10:57:16AM +0800, Guo Ren wrote:
> > On Fri, Dec 22, 2023 at 9:51 AM Leonardo Bras <[email protected]> wrote:
> > >
> > > Hello Guo Ren,
> > >
> > > On Thu, Dec 21, 2023 at 10:46:58AM -0500, [email protected] wrote:
> > > > From: Guo Ren <[email protected]>
> > > >
> > > > In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
> > > > 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
> > > > segment fault. Sometimes, it would cause boot failure when the whole
> > > > rootfs is rv32.
> > >
> > > Checking if I get the scenario:
> > >
> > > In pgtable.h:
> > > #ifdef CONFIG_64BIT
> > > #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
> > > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> > >
> > > #ifdef CONFIG_COMPAT
> > > #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > > TASK_SIZE_32 : TASK_SIZE_64)
> > > #else
> > > [...]
> > >
> > > Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in
> > > compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.
> > >
> > > from processor.h:
> > > #ifdef CONFIG_64BIT
> > > #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
> > > #define STACK_TOP_MAX TASK_SIZE_64
> > > [...]
> > > #define STACK_TOP DEFAULT_MAP_WINDOW
> > >
> > >
> > > where:
> > > #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
> > > with MMAP_VA_BITS_64 being either 48 or 37.
> > >
> > > In compat mode,
> > > STACK_TOP = 1 << (32 - 1) -> 0x80000000
> > > TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000
> > >
> > > IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.
> > Yes, it causes the problem, which causes the boot to fail.
>
> I think what Leonardo is getting at is that it is odd that it would
> cause boot issues if TASK_SIZE is not equal STACK_TOP. This seems
> indicative of a different problem. While this may fix the issue, it
> should be valid for TASK_SIZE to be less than STACK_TOP.
>
> - Charlie
>

That is also a good point, but I am not that acquainted to this to
actually propose this.

I was thinking more on these questions:
Is TASK_SIZE and STACK_TOP related somehow?
If so, would not be better to describe one in terms of the other, like
#define TASK_SIZE (STACK_TOP - PAGE_SIZE)

Or the other way around.

I mean, if they have any relation it would be much easier to represent them
that way, and it would avoid having two magical numbers.

Thanks!
Leo

> >
> > >
> > > Then why not:
> > > #ifdef CONFIG_COMPAT
> > > #define TASK_SIZE_32 STACK_TOP
> > Yes, it's the solution that I think at first. But I didn't find any
> > problem with 0x7ffff000 ~ 0x80000000, and then I removed this gap to
> > unify it with Sv39 and Sv48.
> >
> > >
> > > With some comments explaining why there is no need to reserve a PAGE_SIZE
> > > in the TASK_SIZE_32.
> > At first, I wanted to put a invalid page between the user & kernel
> > space, but it seems useless.
> >
> > >
> > > Does that make sense?
> > >
> > > Thanks!
> > > Leo
> > >
> > > >
> > > > Freeing unused kernel image (initmem) memory: 2236K
> > > > Run /sbin/init as init process
> > > > Starting init: /sbin/init exists but couldn't execute it (error -14)
> > > > Run /etc/init as init process
> > > > ...
> > > >
> > > > Cc: [email protected]
> > > > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> > > > Signed-off-by: Guo Ren <[email protected]>
> > > > Signed-off-by: Guo Ren <[email protected]>
> > > > ---
> > > > arch/riscv/include/asm/pgtable.h | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > > > index ab00235b018f..74ffb2178f54 100644
> > > > --- a/arch/riscv/include/asm/pgtable.h
> > > > +++ b/arch/riscv/include/asm/pgtable.h
> > > > @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> > > > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> > > >
> > > > #ifdef CONFIG_COMPAT
> > > > -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > > > +#define TASK_SIZE_32 (_AC(0x80000000, UL))
> > >
> > >
> > >
> > >
> > > > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > > > TASK_SIZE_32 : TASK_SIZE_64)
> > > > #else
> > > > --
> > > > 2.40.1
> > > >
> > >
> >
> >
> > --
> > Best Regards
> > Guo Ren
>

2023-12-22 07:38:00

by Guo Ren

Subject: Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure

On Fri, Dec 22, 2023 at 12:33 PM Leonardo Bras <[email protected]> wrote:
>
> On Thu, Dec 21, 2023 at 07:50:27PM -0800, Charlie Jenkins wrote:
> > On Fri, Dec 22, 2023 at 10:57:16AM +0800, Guo Ren wrote:
> > > On Fri, Dec 22, 2023 at 9:51 AM Leonardo Bras <[email protected]> wrote:
> > > >
> > > > Hello Guo Ren,
> > > >
> > > > On Thu, Dec 21, 2023 at 10:46:58AM -0500, [email protected] wrote:
> > > > > From: Guo Ren <[email protected]>
> > > > >
> > > > > In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
> > > > > 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
> > > > > segment fault. Sometimes, it would cause boot failure when the whole
> > > > > rootfs is rv32.
> > > >
> > > > Checking if I get the scenario:
> > > >
> > > > In pgtable.h:
> > > > #ifdef CONFIG_64BIT
> > > > #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
> > > > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> > > >
> > > > #ifdef CONFIG_COMPAT
> > > > #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > > > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > > > TASK_SIZE_32 : TASK_SIZE_64)
> > > > #else
> > > > [...]
> > > >
> > > > Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in
> > > > compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.
> > > >
> > > > from processor.h:
> > > > #ifdef CONFIG_64BIT
> > > > #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
> > > > #define STACK_TOP_MAX TASK_SIZE_64
> > > > [...]
> > > > #define STACK_TOP DEFAULT_MAP_WINDOW
> > > >
> > > >
> > > > where:
> > > > #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
> > > > with MMAP_VA_BITS_64 being either 48 or 37.
> > > >
> > > > In compat mode,
> > > > STACK_TOP = 1 << (32 - 1) -> 0x80000000
> > > > TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000
> > > >
> > > > IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.
> > > Yes, it causes the problem, which causes the boot to fail.
> >
> > I think what Leonardo is getting at is that it is odd that it would
> > cause boot issues if TASK_SIZE is not equal STACK_TOP. This seems
> > indicative of a different problem. While this may fix the issue, it
> > should be valid for TASK_SIZE to be less than STACK_TOP.
> >
> > - Charlie
> >
>
> That is also a good point, but I am not that acquainted to this to
> actually propose this.
>
> I was thinking more on these questions:
> Is TASK_SIZE and STACK_TOP related somehow?
> If so, would not be better to describe one in terms of the other, like
> #define TASK_SIZE (STACK_TOP - PAGE_SIZE)
TASK_SIZE means the maximum user address space, so it's the limitation
to any kind of mmap or stack ...
So STACK_TOP <= TASK_SIZE

Follow your idea. The question is:
#define TASK_SIZE ((UL(1) << (VA_BITS - 1)) - PAGE_SIZE)

Do we need to reserve one page between userspace & kernel?


>
> Or the other way around.
>
> I mean, if they have any relation it would be much easier to represent them
> that way, and it would avoid having two magical numbers.
>
> Thanks!
> Leo
>
> > >
> > > >
> > > > Then why not:
> > > > #ifdef CONFIG_COMPAT
> > > > #define TASK_SIZE_32 STACK_TOP
> > > Yes, it's the solution that I think at first. But I didn't find any
> > > problem with 0x7ffff000 ~ 0x80000000, and then I removed this gap to
> > > unify it with Sv39 and Sv48.
> > >
> > > >
> > > > With some comments explaining why there is no need to reserve a PAGE_SIZE
> > > > in the TASK_SIZE_32.
> > > At first, I wanted to put a invalid page between the user & kernel
> > > space, but it seems useless.
> > >
> > > >
> > > > Does that make sense?
> > > >
> > > > Thanks!
> > > > Leo
> > > >
> > > > >
> > > > > Freeing unused kernel image (initmem) memory: 2236K
> > > > > Run /sbin/init as init process
> > > > > Starting init: /sbin/init exists but couldn't execute it (error -14)
> > > > > Run /etc/init as init process
> > > > > ...
> > > > >
> > > > > Cc: [email protected]
> > > > > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> > > > > Signed-off-by: Guo Ren <[email protected]>
> > > > > Signed-off-by: Guo Ren <[email protected]>
> > > > > ---
> > > > > arch/riscv/include/asm/pgtable.h | 2 +-
> > > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > > > > index ab00235b018f..74ffb2178f54 100644
> > > > > --- a/arch/riscv/include/asm/pgtable.h
> > > > > +++ b/arch/riscv/include/asm/pgtable.h
> > > > > @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> > > > > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> > > > >
> > > > > #ifdef CONFIG_COMPAT
> > > > > -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > > > > +#define TASK_SIZE_32 (_AC(0x80000000, UL))
> > > >
> > > >
> > > >
> > > >
> > > > > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > > > > TASK_SIZE_32 : TASK_SIZE_64)
> > > > > #else
> > > > > --
> > > > > 2.40.1
> > > > >
> > > >
> > >
> > >
> > > --
> > > Best Regards
> > > Guo Ren
> >
>


--
Best Regards
Guo Ren

2023-12-22 10:58:31

by Guo Ren

Subject: Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure

Hello Charlie,

On Fri, Dec 22, 2023 at 11:50 AM Charlie Jenkins <[email protected]> wrote:
>
> On Fri, Dec 22, 2023 at 10:57:16AM +0800, Guo Ren wrote:
> > On Fri, Dec 22, 2023 at 9:51 AM Leonardo Bras <[email protected]> wrote:
> > >
> > > Hello Guo Ren,
> > >
> > > On Thu, Dec 21, 2023 at 10:46:58AM -0500, [email protected] wrote:
> > > > From: Guo Ren <[email protected]>
> > > >
> > > > In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
> > > > 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
> > > > segment fault. Sometimes, it would cause boot failure when the whole
> > > > rootfs is rv32.
> > >
> > > Checking if I get the scenario:
> > >
> > > In pgtable.h:
> > > #ifdef CONFIG_64BIT
> > > #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
> > > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> > >
> > > #ifdef CONFIG_COMPAT
> > > #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > > TASK_SIZE_32 : TASK_SIZE_64)
> > > #else
> > > [...]
> > >
> > > Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in
> > > compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.
> > >
> > > from processor.h:
> > > #ifdef CONFIG_64BIT
> > > #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
> > > #define STACK_TOP_MAX TASK_SIZE_64
> > > [...]
> > > #define STACK_TOP DEFAULT_MAP_WINDOW
> > >
> > >
> > > where:
> > > #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
> > > with MMAP_VA_BITS_64 being either 48 or 37.
> > >
> > > In compat mode,
> > > STACK_TOP = 1 << (32 - 1) -> 0x80000000
> > > TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000
> > >
> > > IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.
> > Yes, it causes the problem, which causes the boot to fail.
>
> I think what Leonardo is getting at is that it is odd that it would
> cause boot issues if TASK_SIZE is not equal STACK_TOP. This seems
> indicative of a different problem. While this may fix the issue, it
> should be valid for TASK_SIZE to be less than STACK_TOP.
Sorry, I don't make sense here. Why do you think STACK_TOP could > TASK_SIZE?
TASK_SIZE is the highest priority of the address limitation for
user-space address, right?

Do you mean:
STACK_TOP could > MMAP_END?

>
> - Charlie
>
> >
> > >
> > > Then why not:
> > > #ifdef CONFIG_COMPAT
> > > #define TASK_SIZE_32 STACK_TOP
> > Yes, it's the solution that I think at first. But I didn't find any
> > problem with 0x7ffff000 ~ 0x80000000, and then I removed this gap to
> > unify it with Sv39 and Sv48.
> >
> > >
> > > With some comments explaining why there is no need to reserve a PAGE_SIZE
> > > in the TASK_SIZE_32.
> > At first, I wanted to put a invalid page between the user & kernel
> > space, but it seems useless.
> >
> > >
> > > Does that make sense?
> > >
> > > Thanks!
> > > Leo
> > >
> > > >
> > > > Freeing unused kernel image (initmem) memory: 2236K
> > > > Run /sbin/init as init process
> > > > Starting init: /sbin/init exists but couldn't execute it (error -14)
> > > > Run /etc/init as init process
> > > > ...
> > > >
> > > > Cc: [email protected]
> > > > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> > > > Signed-off-by: Guo Ren <[email protected]>
> > > > Signed-off-by: Guo Ren <[email protected]>
> > > > ---
> > > > arch/riscv/include/asm/pgtable.h | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > > > index ab00235b018f..74ffb2178f54 100644
> > > > --- a/arch/riscv/include/asm/pgtable.h
> > > > +++ b/arch/riscv/include/asm/pgtable.h
> > > > @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> > > > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> > > >
> > > > #ifdef CONFIG_COMPAT
> > > > -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> > > > +#define TASK_SIZE_32 (_AC(0x80000000, UL))
> > >
> > >
> > >
> > >
> > > > #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> > > > TASK_SIZE_32 : TASK_SIZE_64)
> > > > #else
> > > > --
> > > > 2.40.1
> > > >
> > >
> >
> >
> > --
> > Best Regards
> > Guo Ren



--
Best Regards
Guo Ren