Hi Mike, On 8/30/2022 7:40 AM, Mike Kravetz wrote:
During discussions of this series [1], it was suggested that hugetlb handling code in follow_page_mask could be simplified. At the beginning of follow_page_mask, there currently is a call to follow_huge_addr which 'may' handle hugetlb pages. ia64 is the only architecture which provides a follow_huge_addr routine that does not return error. Instead, at each level of the page table a check is made for a hugetlb entry. If a hugetlb entry is found, a call to a routine associated with that entry is made. Currently, there are two checks for hugetlb entries at each page table level. The first check is of the form: if (p?d_huge()) page = follow_huge_p?d(); the second check is of the form: if (is_hugepd()) page = follow_huge_pd(). We can replace these checks, as well as the special handling routines such as follow_huge_p?d() and follow_huge_pd() with a single routine to handle hugetlb vmas. A new routine hugetlb_follow_page_mask is called for hugetlb vmas at the beginning of follow_page_mask. hugetlb_follow_page_mask will use the existing routine huge_pte_offset to walk page tables looking for hugetlb entries. huge_pte_offset can be overwritten by architectures, and already handles special cases such as hugepd entries.
Could you also mention that this patch will fix the lock issue for CONT-PTE/PMD hugetlb by changing to use huge_pte_lock()? which will help people to understand the issue.
Otherwise the changes look good to me. Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
[1] https://lore.kernel.org/linux-mm/cover.1661240170.git.baolin.wang@xxxxxxxxxxxxxxxxx/ Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> --- arch/ia64/mm/hugetlbpage.c | 15 --- arch/powerpc/mm/hugetlbpage.c | 37 -------- include/linux/hugetlb.h | 51 ++-------- mm/gup.c | 65 ++----------- mm/hugetlb.c | 173 +++++++++++----------------------- 5 files changed, 74 insertions(+), 267 deletions(-) diff --git a/arch/ia64/mm/hugetlbpage.c b/arch/ia64/mm/hugetlbpage.c index f993cb36c062..380d2f3966c9 100644 --- a/arch/ia64/mm/hugetlbpage.c +++ b/arch/ia64/mm/hugetlbpage.c @@ -91,21 +91,6 @@ int prepare_hugepage_range(struct file *file, return 0; }-struct page *follow_huge_addr(struct mm_struct *mm, unsigned long addr, int write)-{ - struct page *page; - pte_t *ptep; - - if (REGION_NUMBER(addr) != RGN_HPAGE) - return ERR_PTR(-EINVAL); - - ptep = huge_pte_offset(mm, addr, HPAGE_SIZE); - if (!ptep || pte_none(*ptep)) - return NULL; - page = pte_page(*ptep); - page += ((addr & ~HPAGE_MASK) >> PAGE_SHIFT); - return page; -} int pmd_huge(pmd_t pmd) { return 0; diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c index bc84a594ca62..b0e037c75c12 100644 --- a/arch/powerpc/mm/hugetlbpage.c +++ b/arch/powerpc/mm/hugetlbpage.c @@ -506,43 +506,6 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb, } while (addr = next, addr != end); }-struct page *follow_huge_pd(struct vm_area_struct *vma,- unsigned long address, hugepd_t hpd, - int flags, int pdshift) -{ - pte_t *ptep; - spinlock_t *ptl; - struct page *page = NULL; - unsigned long mask; - int shift = hugepd_shift(hpd); - struct mm_struct *mm = vma->vm_mm; - -retry: - /* - * hugepage directory entries are protected by mm->page_table_lock - * Use this instead of huge_pte_lockptr - */ - ptl = &mm->page_table_lock; - spin_lock(ptl); - - ptep = hugepte_offset(hpd, address, pdshift); - if (pte_present(*ptep)) { - mask = (1UL << shift) - 1; - page = pte_page(*ptep); - page += ((address & mask) >> PAGE_SHIFT); - if (flags & FOLL_GET) - get_page(page); - } else { - if (is_hugetlb_entry_migration(*ptep)) { - spin_unlock(ptl); - __migration_entry_wait(mm, ptep, ptl); - goto retry; - } - } - spin_unlock(ptl); - return page; -} - bool __init arch_hugetlb_valid_size(unsigned long size) { int shift = __ffs(size); diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 852f911d676e..8ea3e5e726e4 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -142,6 +142,8 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, unsigned long len); int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *, struct vm_area_struct *, struct vm_area_struct *); +struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma, + unsigned long address, unsigned int flags); long follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *, struct page **, struct vm_area_struct **, unsigned long *, unsigned long *, long, unsigned int, @@ -202,17 +204,6 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, pte_t *ptep); void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end); -struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address, - int write); -struct page *follow_huge_pd(struct vm_area_struct *vma, - unsigned long address, hugepd_t hpd, - int flags, int pdshift); -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); -struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address, - pgd_t *pgd, int flags);void hugetlb_vma_lock_read(struct vm_area_struct *vma);void hugetlb_vma_unlock_read(struct vm_area_struct *vma); @@ -264,6 +255,13 @@ static inline void adjust_range_if_pmd_sharing_possible( { }+static struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,+ unsigned long address, unsigned int flags) +{ + /* should never happen, but do not want to BUG */ + return ERR_PTR(-EINVAL); +} + static inline long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, unsigned long *position, @@ -274,12 +272,6 @@ static inline long follow_hugetlb_page(struct mm_struct *mm, return 0; }-static inline struct page *follow_huge_addr(struct mm_struct *mm,- unsigned long address, int write) -{ - return ERR_PTR(-EINVAL); -} - static inline int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, struct vm_area_struct *dst_vma, @@ -312,31 +304,6 @@ static inline void hugetlb_show_meminfo_node(int nid) { }-static inline struct page *follow_huge_pd(struct vm_area_struct *vma,- unsigned long address, hugepd_t hpd, int flags, - int pdshift) -{ - return NULL; -} - -static inline struct page *follow_huge_pmd(struct mm_struct *mm, - unsigned long address, pmd_t *pmd, int flags) -{ - return NULL; -} - -static inline struct page *follow_huge_pud(struct mm_struct *mm, - unsigned long address, pud_t *pud, int flags) -{ - return NULL; -} - -static inline struct page *follow_huge_pgd(struct mm_struct *mm, - unsigned long address, pgd_t *pgd, int flags) -{ - return NULL; -} - static inline int prepare_hugepage_range(struct file *file, unsigned long addr, unsigned long len) { diff --git a/mm/gup.c b/mm/gup.c index 66d8619e02ad..80ce04a5bae5 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -661,20 +661,6 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, pmdval = READ_ONCE(*pmd); if (pmd_none(pmdval)) return no_page_table(vma, flags); - if (pmd_huge(pmdval) && is_vm_hugetlb_page(vma)) { - page = follow_huge_pmd(mm, address, pmd, flags); - if (page) - return page; - return no_page_table(vma, flags); - } - if (is_hugepd(__hugepd(pmd_val(pmdval)))) { - page = follow_huge_pd(vma, address, - __hugepd(pmd_val(pmdval)), flags, - PMD_SHIFT); - if (page) - return page; - return no_page_table(vma, flags); - } retry: if (!pmd_present(pmdval)) { /* @@ -764,20 +750,6 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma, pud = pud_offset(p4dp, address); if (pud_none(*pud)) return no_page_table(vma, flags); - if (pud_huge(*pud) && is_vm_hugetlb_page(vma)) { - page = follow_huge_pud(mm, address, pud, flags); - if (page) - return page; - return no_page_table(vma, flags); - } - if (is_hugepd(__hugepd(pud_val(*pud)))) { - page = follow_huge_pd(vma, address, - __hugepd(pud_val(*pud)), flags, - PUD_SHIFT); - if (page) - return page; - return no_page_table(vma, flags); - } if (pud_devmap(*pud)) { ptl = pud_lock(mm, pud); page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap); @@ -797,7 +769,6 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma, struct follow_page_context *ctx) { p4d_t *p4d; - struct page *page;p4d = p4d_offset(pgdp, address);if (p4d_none(*p4d)) @@ -806,14 +777,6 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma, if (unlikely(p4d_bad(*p4d))) return no_page_table(vma, flags);- if (is_hugepd(__hugepd(p4d_val(*p4d)))) {- page = follow_huge_pd(vma, address, - __hugepd(p4d_val(*p4d)), flags, - P4D_SHIFT); - if (page) - return page; - return no_page_table(vma, flags); - } return follow_pud_mask(vma, address, p4d, flags, ctx); }@@ -851,10 +814,15 @@ static struct page *follow_page_mask(struct vm_area_struct *vma, ctx->page_mask = 0; - /* make this handle hugepd */- page = follow_huge_addr(mm, address, flags & FOLL_WRITE); - if (!IS_ERR(page)) { - WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN)); + /* + * Call hugetlb_follow_page_mask for hugetlb vmas as it will use + * special hugetlb page table walking code. This eliminates the + * need to check for hugetlb entries in the general walking code. + */ + if (is_vm_hugetlb_page(vma)) { + page = hugetlb_follow_page_mask(vma, address, flags); + if (!page) + page = no_page_table(vma, flags); return page; }@@ -863,21 +831,6 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) return no_page_table(vma, flags);- if (pgd_huge(*pgd)) {- page = follow_huge_pgd(mm, address, pgd, flags); - if (page) - return page; - return no_page_table(vma, flags); - } - if (is_hugepd(__hugepd(pgd_val(*pgd)))) { - page = follow_huge_pd(vma, address, - __hugepd(pgd_val(*pgd)), flags, - PGDIR_SHIFT); - if (page) - return page; - return no_page_table(vma, flags); - } - return follow_p4d_mask(vma, address, pgd, flags, ctx); }diff --git a/mm/hugetlb.c b/mm/hugetlb.cindex d0617d64d718..b3da421ba5be 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6190,6 +6190,62 @@ static inline bool __follow_hugetlb_must_fault(unsigned int flags, pte_t *pte, return false; }+struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,+ unsigned long address, unsigned int flags) +{ + struct hstate *h = hstate_vma(vma); + struct mm_struct *mm = vma->vm_mm; + unsigned long haddr = address & huge_page_mask(h); + struct page *page = NULL; + spinlock_t *ptl; + pte_t *pte, entry; + + /* + * FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via + * follow_hugetlb_page(). + */ + if (WARN_ON_ONCE(flags & FOLL_PIN)) + return NULL; + + pte = huge_pte_offset(mm, haddr, huge_page_size(h)); + if (!pte) + return NULL; + +retry: + ptl = huge_pte_lock(h, mm, pte); + entry = huge_ptep_get(pte); + if (pte_present(entry)) { + page = pte_page(entry) + + ((address & ~huge_page_mask(h)) >> PAGE_SHIFT); + /* + * Note that page may be a sub-page, and with vmemmap + * optimizations the page struct may be read only. + * try_grab_page() will increase the ref count on the + * head page, so this will be OK. + * + * try_grab_page() should always succeed here, because we hold + * the ptl lock and have verified pte_present(). + */ + if (WARN_ON_ONCE(!try_grab_page(page, flags))) { + page = NULL; + goto out; + } + } else { + if (is_hugetlb_entry_migration(entry)) { + spin_unlock(ptl); + __migration_entry_wait_huge(pte, ptl); + goto retry; + } + /* + * hwpoisoned entry is treated as no_page_table in + * follow_page_mask(). + */ + } +out: + spin_unlock(ptl); + return page; +} + long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, unsigned long *position, unsigned long *nr_pages, @@ -7140,123 +7196,6 @@ __weak unsigned long hugetlb_mask_last_page(struct hstate *h) * These functions are overwritable if your architecture needs its own * behavior. */ -struct page * __weak -follow_huge_addr(struct mm_struct *mm, unsigned long address, - int write) -{ - return ERR_PTR(-EINVAL); -} - -struct page * __weak -follow_huge_pd(struct vm_area_struct *vma, - unsigned long address, hugepd_t hpd, int flags, int pdshift) -{ - WARN(1, "hugepd follow called with no support for hugepage directory format\n"); - return NULL; -} - -struct page * __weak -follow_huge_pmd(struct mm_struct *mm, unsigned long address, - pmd_t *pmd, int flags) -{ - struct page *page = NULL; - spinlock_t *ptl; - pte_t pte; - - /* - * FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via - * follow_hugetlb_page(). - */ - if (WARN_ON_ONCE(flags & FOLL_PIN)) - return NULL; - -retry: - ptl = pmd_lockptr(mm, pmd); - spin_lock(ptl); - /* - * make sure that the address range covered by this pmd is not - * unmapped from other threads. - */ - if (!pmd_huge(*pmd)) - goto out; - pte = huge_ptep_get((pte_t *)pmd); - if (pte_present(pte)) { - page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); - /* - * try_grab_page() should always succeed here, because: a) we - * hold the pmd (ptl) lock, and b) we've just checked that the - * huge pmd (head) page is present in the page tables. The ptl - * prevents the head page and tail pages from being rearranged - * in any way. So this page must be available at this point, - * unless the page refcount overflowed: - */ - if (WARN_ON_ONCE(!try_grab_page(page, flags))) { - page = NULL; - goto out; - } - } else { - if (is_hugetlb_entry_migration(pte)) { - spin_unlock(ptl); - __migration_entry_wait_huge((pte_t *)pmd, ptl); - goto retry; - } - /* - * hwpoisoned entry is treated as no_page_table in - * follow_page_mask(). - */ - } -out: - spin_unlock(ptl); - return page; -} - -struct page * __weak -follow_huge_pud(struct mm_struct *mm, unsigned long address, - pud_t *pud, int flags) -{ - struct page *page = NULL; - spinlock_t *ptl; - pte_t pte; - - if (WARN_ON_ONCE(flags & FOLL_PIN)) - return NULL; - -retry: - ptl = huge_pte_lock(hstate_sizelog(PUD_SHIFT), mm, (pte_t *)pud); - if (!pud_huge(*pud)) - goto out; - pte = huge_ptep_get((pte_t *)pud); - if (pte_present(pte)) { - page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT); - if (WARN_ON_ONCE(!try_grab_page(page, flags))) { - page = NULL; - goto out; - } - } else { - if (is_hugetlb_entry_migration(pte)) { - spin_unlock(ptl); - __migration_entry_wait(mm, (pte_t *)pud, ptl); - goto retry; - } - /* - * hwpoisoned entry is treated as no_page_table in - * follow_page_mask(). - */ - } -out: - spin_unlock(ptl); - return page; -} - -struct page * __weak -follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int flags) -{ - if (flags & (FOLL_GET | FOLL_PIN)) - return NULL; - - return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT); -} - int isolate_hugetlb(struct page *page, struct list_head *list) { int ret = 0;
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