gup_hugepte() checks if pages are present and readable, and
when 'write' is set, also checks if the pages are writable.
Initially this was done by checking if _PAGE_PRESENT and
_PAGE_READ were set. In addition, _PAGE_WRITE was verified for write
accesses.
The problem is that we have to handle the three following cases:
1/ The target defines __PAGE_READ and __PAGE_WRITE
2/ The target defines __PAGE_RW
3/ The target defines __PAGE_RO
In case 1/, this is obvious
In case 2/, __PAGE_READ is defined as 0 and __PAGE_WRITE as __PAGE_RW
so it works as well.
But in case 3, __PAGE_RW is defined as 0, which means __PAGE_WRITE is 0
and then the test returns true (page writable) in all cases.
A first correction was attempted in commit 6b8cb66a6a7cc ("powerpc: Fix
usage of _PAGE_RO in hugepage"), but that fix is wrong:
instead of checking that the page is writable when write is requested,
it checks that the page is NOT writable when write is NOT requested.
This patch adds a new pte_read() helper to check whether a page is
readable or not. This avoids handling all possible cases in
gup_hugepte().
Then gup_hugepte() is modified to use pte_present(), pte_read()
and pte_write() instead of the raw flags.
Signed-off-by: Christophe Leroy <[email protected]>
---
arch/powerpc/include/asm/book3s/32/pgtable.h | 1 +
arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++
arch/powerpc/include/asm/nohash/pgtable.h | 1 +
arch/powerpc/mm/hugetlbpage.c | 15 +++------------
4 files changed, 10 insertions(+), 12 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
index 7fb755880409..2a67b861e6e1 100644
--- a/arch/powerpc/include/asm/book3s/32/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
@@ -301,6 +301,7 @@ int map_kernel_page(unsigned long va, phys_addr_t pa, int flags);
/* Generic accessors to PTE bits */
static inline int pte_write(pte_t pte) { return !!(pte_val(pte) & _PAGE_RW);}
+static inline int pte_read(pte_t pte) { return 1; }
static inline int pte_dirty(pte_t pte) { return !!(pte_val(pte) & _PAGE_DIRTY); }
static inline int pte_young(pte_t pte) { return !!(pte_val(pte) & _PAGE_ACCESSED); }
static inline int pte_special(pte_t pte) { return !!(pte_val(pte) & _PAGE_SPECIAL); }
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index c0737c86a362..83cb73c8c3bb 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -409,6 +409,11 @@ static inline int pte_write(pte_t pte)
return __pte_write(pte) || pte_savedwrite(pte);
}
+static inline int pte_read(pte_t pte)
+{
+ return !!(pte_raw(pte) & cpu_to_be64(_PAGE_READ));
+}
+
#define __HAVE_ARCH_PTEP_SET_WRPROTECT
static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
pte_t *ptep)
diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
index e5805ad78e12..17989c3d9a24 100644
--- a/arch/powerpc/include/asm/nohash/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/pgtable.h
@@ -14,6 +14,7 @@ static inline int pte_write(pte_t pte)
{
return (pte_val(pte) & (_PAGE_RW | _PAGE_RO)) != _PAGE_RO;
}
+static inline int pte_read(pte_t pte) { return 1; }
static inline int pte_dirty(pte_t pte) { return pte_val(pte) & _PAGE_DIRTY; }
static inline int pte_young(pte_t pte) { return pte_val(pte) & _PAGE_ACCESSED; }
static inline int pte_special(pte_t pte) { return pte_val(pte) & _PAGE_SPECIAL; }
diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index e1bf5ca397fe..1226932579a0 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -977,7 +977,6 @@ EXPORT_SYMBOL_GPL(__find_linux_pte_or_hugepte);
int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
- unsigned long mask;
unsigned long pte_end;
struct page *head, *page;
pte_t pte;
@@ -988,18 +987,10 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
end = pte_end;
pte = READ_ONCE(*ptep);
- mask = _PAGE_PRESENT | _PAGE_READ;
-
- /*
- * On some CPUs like the 8xx, _PAGE_RW hence _PAGE_WRITE is defined
- * as 0 and _PAGE_RO has to be set when a page is not writable
- */
- if (write)
- mask |= _PAGE_WRITE;
- else
- mask |= _PAGE_RO;
- if ((pte_val(pte) & mask) != mask)
+ if (!pte_present(pte) || !pte_read(pte))
+ return 0;
+ if (write && !pte_write(pte))
return 0;
/* hugepages are never "special" */
--
2.12.0
Christophe Leroy <[email protected]> writes:
> gup_hugepte() checks if pages are present and readable, and
> when 'write' is set, also checks if the pages are writable.
>
> Initially this was done by checking if _PAGE_PRESENT and
> _PAGE_READ were set. In addition, _PAGE_WRITE was verified for write
> accesses.
>
> The problem is that we have to handle the three following cases:
> 1/ The target defines __PAGE_READ and __PAGE_WRITE
> 2/ The target defines __PAGE_RW
> 3/ The target defines __PAGE_RO
>
> In case 1/, this is obvious
> In case 2/, __PAGE_READ is defined as 0 and __PAGE_WRITE as __PAGE_RW
> so it works as well.
> But in case 3, __PAGE_RW is defined as 0, which means __PAGE_WRITE is 0
> and then the test returns true (page writable) in all cases.
>
> A first correction was attempted in commit 6b8cb66a6a7cc ("powerpc: Fix
> usage of _PAGE_RO in hugepage"), but that fix is wrong:
> instead of checking that the page is writable when write is requested,
> it checks that the page is NOT writable when write is NOT requested.
>
> This patch adds a new pte_read() helper to check whether a page is
> readable or not. This avoids handling all possible cases in
> gup_hugepte().
>
> Then gup_hugepte() is modified to use pte_present(), pte_read()
> and pte_write() instead of the raw flags.
>
Reviewed-by: Aneesh Kumar K.V <[email protected]>
> Signed-off-by: Christophe Leroy <[email protected]>
> ---
> arch/powerpc/include/asm/book3s/32/pgtable.h | 1 +
> arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++
> arch/powerpc/include/asm/nohash/pgtable.h | 1 +
> arch/powerpc/mm/hugetlbpage.c | 15 +++------------
> 4 files changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
> index 7fb755880409..2a67b861e6e1 100644
> --- a/arch/powerpc/include/asm/book3s/32/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
> @@ -301,6 +301,7 @@ int map_kernel_page(unsigned long va, phys_addr_t pa, int flags);
>
> /* Generic accessors to PTE bits */
> static inline int pte_write(pte_t pte) { return !!(pte_val(pte) & _PAGE_RW);}
> +static inline int pte_read(pte_t pte) { return 1; }
> static inline int pte_dirty(pte_t pte) { return !!(pte_val(pte) & _PAGE_DIRTY); }
> static inline int pte_young(pte_t pte) { return !!(pte_val(pte) & _PAGE_ACCESSED); }
> static inline int pte_special(pte_t pte) { return !!(pte_val(pte) & _PAGE_SPECIAL); }
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index c0737c86a362..83cb73c8c3bb 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -409,6 +409,11 @@ static inline int pte_write(pte_t pte)
> return __pte_write(pte) || pte_savedwrite(pte);
> }
>
> +static inline int pte_read(pte_t pte)
> +{
> + return !!(pte_raw(pte) & cpu_to_be64(_PAGE_READ));
> +}
> +
> #define __HAVE_ARCH_PTEP_SET_WRPROTECT
> static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep)
> diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
> index e5805ad78e12..17989c3d9a24 100644
> --- a/arch/powerpc/include/asm/nohash/pgtable.h
> +++ b/arch/powerpc/include/asm/nohash/pgtable.h
> @@ -14,6 +14,7 @@ static inline int pte_write(pte_t pte)
> {
> return (pte_val(pte) & (_PAGE_RW | _PAGE_RO)) != _PAGE_RO;
> }
> +static inline int pte_read(pte_t pte) { return 1; }
> static inline int pte_dirty(pte_t pte) { return pte_val(pte) & _PAGE_DIRTY; }
> static inline int pte_young(pte_t pte) { return pte_val(pte) & _PAGE_ACCESSED; }
> static inline int pte_special(pte_t pte) { return pte_val(pte) & _PAGE_SPECIAL; }
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index e1bf5ca397fe..1226932579a0 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -977,7 +977,6 @@ EXPORT_SYMBOL_GPL(__find_linux_pte_or_hugepte);
> int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> unsigned long end, int write, struct page **pages, int *nr)
> {
> - unsigned long mask;
> unsigned long pte_end;
> struct page *head, *page;
> pte_t pte;
> @@ -988,18 +987,10 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> end = pte_end;
>
> pte = READ_ONCE(*ptep);
> - mask = _PAGE_PRESENT | _PAGE_READ;
> -
> - /*
> - * On some CPUs like the 8xx, _PAGE_RW hence _PAGE_WRITE is defined
> - * as 0 and _PAGE_RO has to be set when a page is not writable
> - */
> - if (write)
> - mask |= _PAGE_WRITE;
> - else
> - mask |= _PAGE_RO;
>
> - if ((pte_val(pte) & mask) != mask)
> + if (!pte_present(pte) || !pte_read(pte))
> + return 0;
> + if (write && !pte_write(pte))
> return 0;
>
> /* hugepages are never "special" */
> --
> 2.12.0
On Wed, 2017-07-12 at 15:03:42 UTC, Christophe Leroy wrote:
> gup_hugepte() checks if pages are present and readable, and
> when 'write' is set, also checks if the pages are writable.
>
> Initially this was done by checking if _PAGE_PRESENT and
> _PAGE_READ were set. In addition, _PAGE_WRITE was verified for write
> accesses.
>
> The problem is that we have to handle the three following cases:
> 1/ The target defines __PAGE_READ and __PAGE_WRITE
> 2/ The target defines __PAGE_RW
> 3/ The target defines __PAGE_RO
>
> In case 1/, this is obvious
> In case 2/, __PAGE_READ is defined as 0 and __PAGE_WRITE as __PAGE_RW
> so it works as well.
> But in case 3, __PAGE_RW is defined as 0, which means __PAGE_WRITE is 0
> and then the test returns true (page writable) in all cases.
>
> A first correction was attempted in commit 6b8cb66a6a7cc ("powerpc: Fix
> usage of _PAGE_RO in hugepage"), but that fix is wrong:
> instead of checking that the page is writable when write is requested,
> it checks that the page is NOT writable when write is NOT requested.
>
> This patch adds a new pte_read() helper to check whether a page is
> readable or not. This avoids handling all possible cases in
> gup_hugepte().
>
> Then gup_hugepte() is modified to use pte_present(), pte_read()
> and pte_write() instead of the raw flags.
>
> Signed-off-by: Christophe Leroy <[email protected]>
> Reviewed-by: Aneesh Kumar K.V <[email protected]>
Applied to powerpc next, thanks.
https://git.kernel.org/powerpc/c/ca8afd4046255ac046f8229d5159c6
cheers