On 8 June 2017 at 12:59, Mark Rutland <mark.rutland@xxxxxxx> wrote: > On Thu, Jun 08, 2017 at 11:35:48AM +0000, Ard Biesheuvel wrote: >> Existing code that uses vmalloc_to_page() may assume that any >> address for which is_vmalloc_addr() returns true may be passed >> into vmalloc_to_page() to retrieve the associated struct page. >> >> This is not un unreasonable assumption to make, but on architectures >> that have CONFIG_HAVE_ARCH_HUGE_VMAP=y, it no longer holds, and we >> need to ensure that vmalloc_to_page() does not go off into the weeds >> trying to dereference huge PUDs or PMDs as table entries. >> >> Given that vmalloc() and vmap() themselves never create huge >> mappings or deal with compound pages at all, there is no correct >> value to return in this case, so return NULL instead, and issue a >> warning. >> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> >> --- >> This is a followup to '[PATCH v2] mm: vmalloc: make vmalloc_to_page() >> deal with PMD/PUD mappings', hence the v3. The root issue with /proc/kcore >> on arm64 is now handled by '[PATCH] mm: vmalloc: simplify vread/vwrite to >> use existing mappings' [1], and this patch now only complements it by >> taking care of other vmalloc_to_page() users. >> >> [0] http://marc.info/?l=linux-mm&m=149641886821855&w=2 >> [1] http://marc.info/?l=linux-mm&m=149685966530180&w=2 >> >> include/linux/hugetlb.h | 13 +++++++++---- >> mm/vmalloc.c | 5 +++-- >> 2 files changed, 12 insertions(+), 6 deletions(-) >> >> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h >> index b857fc8cc2ec..b7166e5426b6 100644 >> --- a/include/linux/hugetlb.h >> +++ b/include/linux/hugetlb.h >> @@ -121,8 +121,6 @@ struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address, >> pmd_t *pmd, int flags); >> struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address, >> pud_t *pud, int flags); >> -int pmd_huge(pmd_t pmd); >> -int pud_huge(pud_t pud); >> unsigned long hugetlb_change_protection(struct vm_area_struct *vma, >> unsigned long address, unsigned long end, pgprot_t newprot); >> >> @@ -150,8 +148,6 @@ static inline void hugetlb_show_meminfo(void) >> #define follow_huge_pmd(mm, addr, pmd, flags) NULL >> #define follow_huge_pud(mm, addr, pud, flags) NULL >> #define prepare_hugepage_range(file, addr, len) (-EINVAL) >> -#define pmd_huge(x) 0 >> -#define pud_huge(x) 0 >> #define is_hugepage_only_range(mm, addr, len) 0 >> #define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) ({BUG(); 0; }) >> #define hugetlb_fault(mm, vma, addr, flags) ({ BUG(); 0; }) >> @@ -190,6 +186,15 @@ static inline void __unmap_hugepage_range(struct mmu_gather *tlb, >> } >> >> #endif /* !CONFIG_HUGETLB_PAGE */ >> + >> +#if defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_HAVE_ARCH_HUGE_VMAP) >> +int pmd_huge(pmd_t pmd); >> +int pud_huge(pud_t pud); >> +#else >> +#define pmd_huge(x) 0 >> +#define pud_huge(x) 0 >> +#endif >> + >> /* >> * hugepages at page global directory. If arch support >> * hugepages at pgd level, they need to define this. >> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >> index 982d29511f92..67e1a304c467 100644 >> --- a/mm/vmalloc.c >> +++ b/mm/vmalloc.c >> @@ -12,6 +12,7 @@ >> #include <linux/mm.h> >> #include <linux/module.h> >> #include <linux/highmem.h> >> +#include <linux/hugetlb.h> >> #include <linux/sched/signal.h> >> #include <linux/slab.h> >> #include <linux/spinlock.h> >> @@ -287,10 +288,10 @@ struct page *vmalloc_to_page(const void *vmalloc_addr) >> if (p4d_none(*p4d)) >> return NULL; >> pud = pud_offset(p4d, addr); >> - if (pud_none(*pud)) >> + if (pud_none(*pud) || WARN_ON_ONCE(pud_huge(*pud))) >> return NULL; >> pmd = pmd_offset(pud, addr); >> - if (pmd_none(*pmd)) >> + if (pmd_none(*pmd) || WARN_ON_ONCE(pmd_huge(*pmd))) >> return NULL; > > I think it might be better to use p*d_bad() here, since that doesn't > depend on CONFIG_HUGETLB_PAGE. > > While the cross-arch semantics are a little fuzzy, my understanding is > those should return true if an entry is not a pointer to a next level of > table (so pXd_huge(p) implies pXd_bad(p)). > Fair enough. It is slightly counter intuitive, but I guess this is due to historical reasons, and is unlikely to change in the future. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
