From: Lorenzo Stoakes (Oracle) Date: Fri, 20 Mar 2026 18:07:18 +0000 (+0000) Subject: mm/huge_memory: simplify vma_is_specal_huge() X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=c0ea52c18c78c33c68c350eb9d3dcdf8c513254d;p=thirdparty%2Fkernel%2Flinux.git mm/huge_memory: simplify vma_is_specal_huge() Patch series "mm/huge_memory: refactor zap_huge_pmd()", v3. zap_huge_pmd() is overly complicated, clean it up and also add an assert in the case that we encounter a buggy PMD entry that doesn't match expectations. This is motivated by a bug discovered [0] where the PMD entry was none of: * A non-DAX, PFN or mixed map. * The huge zero folio * A present PMD entry * A softleaf entry In zap_huge_pmd(), but due to the bug we manged to reach this code. It is useful to explicitly call this out rather than have an arbitrary NULL pointer dereference happen, which also improves understanding of what's going on. The series goes further to make use of vm_normal_folio_pmd() rather than implementing custom logic for retrieving the folio, and extends softleaf functionality to provide and use an equivalent softleaf function. This patch (of 13): This function is confused - it overloads the term 'special' yet again, checks for DAX but in many cases the code explicitly excludes DAX before invoking the predicate. It also unnecessarily checks for vma->vm_file - this has to be present for a driver to have set VMA_MIXEDMAP_BIT or VMA_PFNMAP_BIT. In fact, a far simpler form of this is to reverse the DAX predicate and return false if DAX is set. This makes sense from the point of view of 'special' as in vm_normal_page(), as DAX actually does potentially have retrievable folios. Also there's no need to have this in mm.h so move it to huge_memory.c. No functional change intended. Link: https://lkml.kernel.org/r/cover.1774029655.git.ljs@kernel.org Link: https://lkml.kernel.org/r/d2b65883dc4895f197c4b4a69fbf27a063463412.1774029655.git.ljs@kernel.org Link: https://lore.kernel.org/all/6b3d7ad7-49e1-407a-903d-3103704160d8@lucifer.local/ [0] Signed-off-by: Lorenzo Stoakes (Oracle) Reviewed-by: Suren Baghdasaryan Cc: Baolin Wang Cc: Barry Song Cc: David Hildenbrand Cc: Dev Jain Cc: Lance Yang Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Nico Pache Cc: Ryan Roberts Cc: Zi Yan Cc: Qi Zheng Signed-off-by: Andrew Morton --- diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index bd7f0e1d80945..61fda1672b292 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -83,7 +83,7 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr; * file is never split and the MAX_PAGECACHE_ORDER limit does not apply to * it. Same to PFNMAPs where there's neither page* nor pagecache. */ -#define THP_ORDERS_ALL_SPECIAL \ +#define THP_ORDERS_ALL_SPECIAL_DAX \ (BIT(PMD_ORDER) | BIT(PUD_ORDER)) #define THP_ORDERS_ALL_FILE_DEFAULT \ ((BIT(MAX_PAGECACHE_ORDER + 1) - 1) & ~BIT(0)) @@ -92,7 +92,7 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr; * Mask of all large folio orders supported for THP. */ #define THP_ORDERS_ALL \ - (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_SPECIAL | THP_ORDERS_ALL_FILE_DEFAULT) + (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_SPECIAL_DAX | THP_ORDERS_ALL_FILE_DEFAULT) enum tva_type { TVA_SMAPS, /* Exposing "THPeligible:" in smaps. */ diff --git a/include/linux/mm.h b/include/linux/mm.h index 61dff7f035541..8260e28205e90 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -5068,22 +5068,6 @@ long copy_folio_from_user(struct folio *dst_folio, const void __user *usr_src, bool allow_pagefault); -/** - * vma_is_special_huge - Are transhuge page-table entries considered special? - * @vma: Pointer to the struct vm_area_struct to consider - * - * Whether transhuge page-table entries are considered "special" following - * the definition in vm_normal_page(). - * - * Return: true if transhuge page-table entries should be considered special, - * false otherwise. - */ -static inline bool vma_is_special_huge(const struct vm_area_struct *vma) -{ - return vma_is_dax(vma) || (vma->vm_file && - (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))); -} - #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */ #if MAX_NUMNODES > 1 diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1c1a7cf7b209b..db390b0098d9e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -100,6 +100,14 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma) return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode); } +/* If returns true, we are unable to access the VMA's folios. */ +static bool vma_is_special_huge(const struct vm_area_struct *vma) +{ + if (vma_is_dax(vma)) + return false; + return vma_test_any(vma, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT); +} + unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, vm_flags_t vm_flags, enum tva_type type, @@ -113,8 +121,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, /* Check the intersection of requested and supported orders. */ if (vma_is_anonymous(vma)) supported_orders = THP_ORDERS_ALL_ANON; - else if (vma_is_special_huge(vma)) - supported_orders = THP_ORDERS_ALL_SPECIAL; + else if (vma_is_dax(vma) || vma_is_special_huge(vma)) + supported_orders = THP_ORDERS_ALL_SPECIAL_DAX; else supported_orders = THP_ORDERS_ALL_FILE_DEFAULT; @@ -2415,7 +2423,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, tlb->fullmm); arch_check_zapped_pmd(vma, orig_pmd); tlb_remove_pmd_tlb_entry(tlb, pmd, addr); - if (!vma_is_dax(vma) && vma_is_special_huge(vma)) { + if (vma_is_special_huge(vma)) { if (arch_needs_pgtable_deposit()) zap_deposited_table(tlb->mm, pmd); spin_unlock(ptl); @@ -2917,7 +2925,7 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma, orig_pud = pudp_huge_get_and_clear_full(vma, addr, pud, tlb->fullmm); arch_check_zapped_pud(vma, orig_pud); tlb_remove_pud_tlb_entry(tlb, pud, addr); - if (!vma_is_dax(vma) && vma_is_special_huge(vma)) { + if (vma_is_special_huge(vma)) { spin_unlock(ptl); /* No zero page support yet */ } else { @@ -3068,7 +3076,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, */ if (arch_needs_pgtable_deposit()) zap_deposited_table(mm, pmd); - if (!vma_is_dax(vma) && vma_is_special_huge(vma)) + if (vma_is_special_huge(vma)) return; if (unlikely(pmd_is_migration_entry(old_pmd))) { const softleaf_t old_entry = softleaf_from_pmd(old_pmd); @@ -4629,8 +4637,16 @@ next: static inline bool vma_not_suitable_for_thp_split(struct vm_area_struct *vma) { - return vma_is_special_huge(vma) || (vma->vm_flags & VM_IO) || - is_vm_hugetlb_page(vma); + if (vma_is_dax(vma)) + return true; + if (vma_is_special_huge(vma)) + return true; + if (vma_test(vma, VMA_IO_BIT)) + return true; + if (is_vm_hugetlb_page(vma)) + return true; + + return false; } static int split_huge_pages_pid(int pid, unsigned long vaddr_start,