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 dgDImTjV BFY/xxlEce/m83ceweOP9ET+d8QTPtc3j3ybTYO5xRednvzEPcDt2kIcSVSYBE9VQx//pMfNLQNR8mRioa3ZNisoBNbuU6/7L0HhCIMtn5aoIZBc4aOOuSvsG79+XT2vIrUXySJWYwrarvPadWAtAGIilUHXTJIOSFgGI/6pyKE2tZHgsVC96iwoPj+hBAlEATsCw/a/te0qj710+KXPRiUGmt3nkWjQMEiA0xUyTBTuM6yS853aUHh4/oeftzRCnDo1edsxMcK1tTU9r+eE7Bc3cNHe4od3t8vNWS29PP80L4dbuNCftXDJu+Pk4HPDIDIxXggTi+MFhly40ceeuRHkyXm+ua7OETQsC7yrdcrFdmnB2Au8guqRbTMtgQwDCXwMnbd0+0UsU1nN4lzvr5MHBMIHMmGISrYyAPSNGAti+VrZHaD5YGxx50M8qIWHfJCopCynqFjsNllI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02/18/23 00:27, James Houghton wrote: > hugetlb_hgm_walk implements high-granularity page table walks for > HugeTLB. It is safe to call on non-HGM enabled VMAs; it will return > immediately. > > hugetlb_walk_step implements how we step forwards in the walk. For > architectures that don't use GENERAL_HUGETLB, they will need to provide > their own implementation. > > The broader API that should be used is > hugetlb_full_walk[,alloc|,continue]. I guess 'full' in the name implies walking to the PTE (PAGE_SIZE) level. It could just be me and my over-familiarity with the existing hugetlb walking code, but that was not obvious. Again, perhaps it is just how familiar I am with the existing code, but I found the routines difficult to follow. Nothing looks obviously wrong. Just a couple comments.questions below. > > Signed-off-by: James Houghton > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 9d839519c875..726d581158b1 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -223,6 +223,14 @@ u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx); > pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, > unsigned long addr, pud_t *pud); > > +int hugetlb_full_walk(struct hugetlb_pte *hpte, struct vm_area_struct *vma, > + unsigned long addr); > +void hugetlb_full_walk_continue(struct hugetlb_pte *hpte, > + struct vm_area_struct *vma, unsigned long addr); > +int hugetlb_full_walk_alloc(struct hugetlb_pte *hpte, > + struct vm_area_struct *vma, unsigned long addr, > + unsigned long target_sz); > + > struct address_space *hugetlb_page_mapping_lock_write(struct page *hpage); > > extern int sysctl_hugetlb_shm_group; > @@ -272,6 +280,8 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma, > pte_t *huge_pte_offset(struct mm_struct *mm, > unsigned long addr, unsigned long sz); > unsigned long hugetlb_mask_last_page(struct hstate *h); > +int hugetlb_walk_step(struct mm_struct *mm, struct hugetlb_pte *hpte, > + unsigned long addr, unsigned long sz); > 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, > @@ -1054,6 +1064,8 @@ void hugetlb_register_node(struct node *node); > void hugetlb_unregister_node(struct node *node); > #endif > > +enum hugetlb_level hpage_size_to_level(unsigned long sz); > + > #else /* CONFIG_HUGETLB_PAGE */ > struct hstate {}; > > @@ -1246,6 +1258,11 @@ static inline void hugetlb_register_node(struct node *node) > static inline void hugetlb_unregister_node(struct node *node) > { > } > + > +static inline enum hugetlb_level hpage_size_to_level(unsigned long sz) > +{ > + return HUGETLB_LEVEL_PTE; > +} > #endif /* CONFIG_HUGETLB_PAGE */ > > #ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index bb424cdf79e4..810c05feb41f 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -97,6 +97,29 @@ static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma); > static void hugetlb_unshare_pmds(struct vm_area_struct *vma, > unsigned long start, unsigned long end); > > +/* > + * hpage_size_to_level() - convert @sz to the corresponding page table level > + * > + * @sz must be less than or equal to a valid hugepage size. > + */ > +enum hugetlb_level hpage_size_to_level(unsigned long sz) > +{ > + /* > + * We order the conditionals from smallest to largest to pick the > + * smallest level when multiple levels have the same size (i.e., > + * when levels are folded). > + */ > + if (sz < PMD_SIZE) > + return HUGETLB_LEVEL_PTE; > + if (sz < PUD_SIZE) > + return HUGETLB_LEVEL_PMD; > + if (sz < P4D_SIZE) > + return HUGETLB_LEVEL_PUD; > + if (sz < PGDIR_SIZE) > + return HUGETLB_LEVEL_P4D; > + return HUGETLB_LEVEL_PGD; > +} > + > static inline bool subpool_is_free(struct hugepage_subpool *spool) > { > if (spool->count) > @@ -7315,6 +7338,154 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr) > } > #endif /* CONFIG_ARCH_WANT_HUGE_PMD_SHARE */ > > +/* __hugetlb_hgm_walk - walks a high-granularity HugeTLB page table to resolve > + * the page table entry for @addr. We might allocate new PTEs. > + * > + * @hpte must always be pointing at an hstate-level PTE or deeper. > + * > + * This function will never walk further if it encounters a PTE of a size > + * less than or equal to @sz. > + * > + * @alloc determines what we do when we encounter an empty PTE. If false, > + * we stop walking. If true and @sz is less than the current PTE's size, > + * we make that PTE point to the next level down, going until @sz is the same > + * as our current PTE. > + * > + * If @alloc is false and @sz is PAGE_SIZE, this function will always > + * succeed, but that does not guarantee that hugetlb_pte_size(hpte) is @sz. > + * > + * Return: > + * -ENOMEM if we couldn't allocate new PTEs. > + * -EEXIST if the caller wanted to walk further than a migration PTE, > + * poison PTE, or a PTE marker. The caller needs to manually deal > + * with this scenario. > + * -EINVAL if called with invalid arguments (@sz invalid, @hpte not > + * initialized). > + * 0 otherwise. > + * > + * Even if this function fails, @hpte is guaranteed to always remain > + * valid. > + */ > +static int __hugetlb_hgm_walk(struct mm_struct *mm, struct vm_area_struct *vma, > + struct hugetlb_pte *hpte, unsigned long addr, > + unsigned long sz, bool alloc) > +{ > + int ret = 0; > + pte_t pte; > + > + if (WARN_ON_ONCE(sz < PAGE_SIZE)) > + return -EINVAL; > + > + if (WARN_ON_ONCE(!hpte->ptep)) > + return -EINVAL; > + > + while (hugetlb_pte_size(hpte) > sz && !ret) { > + pte = huge_ptep_get(hpte->ptep); > + if (!pte_present(pte)) { > + if (!alloc) > + return 0; > + if (unlikely(!huge_pte_none(pte))) > + return -EEXIST; > + } else if (hugetlb_pte_present_leaf(hpte, pte)) > + return 0; > + ret = hugetlb_walk_step(mm, hpte, addr, sz); > + } > + > + return ret; > +} > + > +/* > + * hugetlb_hgm_walk - Has the same behavior as __hugetlb_hgm_walk but will > + * initialize @hpte with hstate-level PTE pointer @ptep. > + */ > +static int hugetlb_hgm_walk(struct hugetlb_pte *hpte, > + pte_t *ptep, > + struct vm_area_struct *vma, > + unsigned long addr, > + unsigned long target_sz, > + bool alloc) > +{ > + struct hstate *h = hstate_vma(vma); > + > + hugetlb_pte_init(vma->vm_mm, hpte, ptep, huge_page_shift(h), > + hpage_size_to_level(huge_page_size(h))); > + return __hugetlb_hgm_walk(vma->vm_mm, vma, hpte, addr, target_sz, > + alloc); > +} > + > +/* > + * hugetlb_full_walk_continue - continue a high-granularity page-table walk. > + * > + * If a user has a valid @hpte but knows that @hpte is not a leaf, they can > + * attempt to continue walking by calling this function. > + * > + * This function will never fail, but @hpte might not change. > + * > + * If @hpte hasn't been initialized, then this function's behavior is > + * undefined. > + */ > +void hugetlb_full_walk_continue(struct hugetlb_pte *hpte, > + struct vm_area_struct *vma, > + unsigned long addr) > +{ > + /* __hugetlb_hgm_walk will never fail with these arguments. */ > + WARN_ON_ONCE(__hugetlb_hgm_walk(vma->vm_mm, vma, hpte, addr, > + PAGE_SIZE, false)); > +} > + > +/* > + * hugetlb_full_walk - do a high-granularity page-table walk; never allocate. > + * > + * This function can only fail if we find that the hstate-level PTE is not > + * allocated. Callers can take advantage of this fact to skip address regions > + * that cannot be mapped in that case. > + * > + * If this function succeeds, @hpte is guaranteed to be valid. > + */ > +int hugetlb_full_walk(struct hugetlb_pte *hpte, > + struct vm_area_struct *vma, > + unsigned long addr) > +{ > + struct hstate *h = hstate_vma(vma); > + unsigned long sz = huge_page_size(h); > + /* > + * We must mask the address appropriately so that we pick up the first > + * PTE in a contiguous group. > + */ > + pte_t *ptep = hugetlb_walk(vma, addr & huge_page_mask(h), sz); > + > + if (!ptep) > + return -ENOMEM; -ENOMEM does not seem appropriate, but I can not think of something better. -ENOENT perhaps? > + > + /* hugetlb_hgm_walk will never fail with these arguments. */ > + WARN_ON_ONCE(hugetlb_hgm_walk(hpte, ptep, vma, addr, PAGE_SIZE, false)); > + return 0; > +} > + > +/* > + * hugetlb_full_walk_alloc - do a high-granularity walk, potentially allocate > + * new PTEs. > + */ > +int hugetlb_full_walk_alloc(struct hugetlb_pte *hpte, > + struct vm_area_struct *vma, > + unsigned long addr, > + unsigned long target_sz) > +{ > + struct hstate *h = hstate_vma(vma); > + unsigned long sz = huge_page_size(h); > + /* > + * We must mask the address appropriately so that we pick up the first > + * PTE in a contiguous group. > + */ > + pte_t *ptep = huge_pte_alloc(vma->vm_mm, vma, addr & huge_page_mask(h), > + sz); > + > + if (!ptep) > + return -ENOMEM; > + > + return hugetlb_hgm_walk(hpte, ptep, vma, addr, target_sz, true); > +} > + > #ifdef CONFIG_ARCH_WANT_GENERAL_HUGETLB > pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma, > unsigned long addr, unsigned long sz) > @@ -7382,6 +7553,48 @@ pte_t *huge_pte_offset(struct mm_struct *mm, > return (pte_t *)pmd; > } > > +/* > + * hugetlb_walk_step() - Walk the page table one step to resolve the page > + * (hugepage or subpage) entry at address @addr. > + * > + * @sz always points at the final target PTE size (e.g. PAGE_SIZE for the > + * lowest level PTE). > + * > + * @hpte will always remain valid, even if this function fails. > + * > + * Architectures that implement this function must ensure that if @hpte does > + * not change levels, then its PTL must also stay the same. > + */ > +int hugetlb_walk_step(struct mm_struct *mm, struct hugetlb_pte *hpte, > + unsigned long addr, unsigned long sz) > +{ > + pte_t *ptep; > + spinlock_t *ptl; > + > + switch (hpte->level) { > + case HUGETLB_LEVEL_PUD: > + ptep = (pte_t *)hugetlb_alloc_pmd(mm, hpte, addr); > + if (IS_ERR(ptep)) > + return PTR_ERR(ptep); > + hugetlb_pte_init(mm, hpte, ptep, PMD_SHIFT, > + HUGETLB_LEVEL_PMD); > + break; > + case HUGETLB_LEVEL_PMD: > + ptep = hugetlb_alloc_pte(mm, hpte, addr); > + if (IS_ERR(ptep)) > + return PTR_ERR(ptep); > + ptl = pte_lockptr(mm, (pmd_t *)hpte->ptep); Is that right? hpte->ptep is the PMD level entry. It seems pte_lockptr() -> ptlock_ptr(pmd_page(*pmd)) -> return page->ptl But, I would think we want the page mm->page_table_lock for newly allocated PTE. -- Mike Kravetz > + __hugetlb_pte_init(hpte, ptep, PAGE_SHIFT, > + HUGETLB_LEVEL_PTE, ptl); > + break; > + default: > + WARN_ONCE(1, "%s: got invalid level: %d (shift: %d)\n", > + __func__, hpte->level, hpte->shift); > + return -EINVAL; > + } > + return 0; > +} > + > /* > * Return a mask that can be used to update an address to the last huge > * page in a page table page mapping size. Used to skip non-present > -- > 2.39.2.637.g21b0678d19-goog >