Currently only get_user_pages_fast() can safely handle the writable gup case due to its use of pud_access_permitted() to check whether the pud entry is writable. In the gup slow path pud_write() is used instead of pud_access_permitted() and to date it has been unimplemented, just calls BUG_ON().
kernel BUG at ./include/linux/hugetlb.h:244! [..] RIP: 0010:follow_devmap_pud+0x482/0x490 [..] Call Trace: follow_page_mask+0x28c/0x6e0 __get_user_pages+0xe4/0x6c0 get_user_pages_unlocked+0x130/0x1b0 get_user_pages_fast+0x89/0xb0 iov_iter_get_pages_alloc+0x114/0x4a0 nfs_direct_read_schedule_iovec+0xd2/0x350 ? nfs_start_io_direct+0x63/0x70 nfs_file_direct_read+0x1e0/0x250 nfs_file_read+0x90/0xc0
For now this just implements a simple check for the _PAGE_RW bit similar to pmd_write. However, this implies that the gup-slow-path check is missing the extra checks that the gup-fast-path performs with pud_access_permitted. Later patches will align all checks to use the 'access_permitted' helper if the architecture provides it. Note that the generic 'access_permitted' helper fallback is the simple _PAGE_RW check on architectures that do not define the 'access_permitted' helper(s).
Cc: stable@vger.kernel.org Cc: Dave Hansen dave.hansen@intel.com Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages") Signed-off-by: Dan Williams dan.j.williams@intel.com --- arch/x86/include/asm/pgtable.h | 6 ++++++ include/asm-generic/pgtable.h | 9 +++++++++ include/linux/hugetlb.h | 8 -------- 3 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index f735c3016325..5c396724fd0d 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1093,6 +1093,12 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm, clear_bit(_PAGE_BIT_RW, (unsigned long *)pmdp); }
+#define __HAVE_ARCH_PUD_WRITE +static inline int pud_write(pud_t pud) +{ + return pud_flags(pud) & _PAGE_RW; +} + /* * clone_pgd_range(pgd_t *dst, pgd_t *src, int count); * diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h index 757dc6ffc7ba..bd738624bd16 100644 --- a/include/asm-generic/pgtable.h +++ b/include/asm-generic/pgtable.h @@ -812,6 +812,15 @@ static inline int pmd_write(pmd_t pmd) return 0; } #endif /* __HAVE_ARCH_PMD_WRITE */ + +#ifndef __HAVE_ARCH_PUD_WRITE +static inline int pud_write(pud_t pud) +{ + BUG(); + return 0; +} +#endif /* __HAVE_ARCH_PUD_WRITE */ + #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#if !defined(CONFIG_TRANSPARENT_HUGEPAGE) || \ diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index fbf5b31d47ee..82a25880714a 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -239,14 +239,6 @@ static inline int pgd_write(pgd_t pgd) } #endif
-#ifndef pud_write -static inline int pud_write(pud_t pud) -{ - BUG(); - return 0; -} -#endif - #define HUGETLB_ANON_FILE "anon_hugepage"
enum {