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AKwUvBwSWCAe65SHayG2vR1etfoiLdUbJP5g0tykgvZ0pM414NdDt1B/UYquf8dEW4D8M8Gp2h7/diZHiHU+ENA=@vger.kernel.org X-Gm-Message-State: AFq9FYKLtoBZvnhCSedyaFw+HaIXGEhkXgr5O8w7FGeNflVcVG8x94OC kj4rfRShkgMtTrQihi3eUX4AZ9rHoC6Yu7SZ8IPpuBadgX23Swiwa9+OFmaxH2hBO7qTAlzbIQW Gc+CwhXMZMjpOka++MnSryw== X-Received: from pgby27-n2.prod.google.com ([2002:a05:6a02:651b:20b0:cc7:d8ea:a7b5]) (user=jthoughton job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:134c:b0:39e:6a7e:ee1b with SMTP id 98e67ed59e1d1-3a6ce7db233mr2804158a91.39.1790986898532; Fri, 02 Oct 2026 17:21:38 -0700 (PDT) Date: Sat, 3 Oct 2026 00:21:08 +0000 In-Reply-To: <20261003002123.505555-1-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20261003002123.505555-1-jthoughton@google.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Message-ID: <20261003002123.505555-6-jthoughton@google.com> Subject: [PATCH v2 05/20] hugetlb_vmemmap: Use try_update_vmemmap_pte to update in-use PTEs From: James Houghton To: Will Deacon , Catalin Marinas , Muchun Song , Oscar Salvador , Andrew Morton Cc: Nikos Nikoleris , Linu Cherian , Mark Rutland , David Hildenbrand , Ryan Roberts , Nanyong Sun , Yu Zhao , Frank van der Linden , David Rientjes , James Houghton , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" set_pte_at() cannot be used to replace in-use vmemmap PTEs on arm64, so replace it with a more specific routine, try_update_vmemmap_pte(). try_update_vmemmap_pte() is used for modifying page table entries such that there is a guarantee that no fault will be taken. For the generic implementation, please note one difference: set_pte() does not invoke page_table_check_ptes_set(), but set_pte_at(), the call we are about to replace, does. However, this is a functional no-op because page_table_check_ptes_set() does nothing for init_mm PTEs, which vmemmap PTEs are. Signed-off-by: James Houghton --- arch/loongarch/include/asm/pgtable.h | 2 + arch/riscv/include/asm/pgtable.h | 2 + arch/x86/include/asm/pgtable.h | 2 + include/linux/pgtable.h | 22 +++++++++++ mm/hugetlb_vmemmap.c | 56 +++++++++++++++++++--------- 5 files changed, 67 insertions(+), 17 deletions(-) diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h index f87603135131..123eda3f6035 100644 --- a/arch/loongarch/include/asm/pgtable.h +++ b/arch/loongarch/include/asm/pgtable.h @@ -633,6 +633,8 @@ static inline long pmd_protnone(pmd_t pmd) #define pmd_leaf(pmd) ((pmd_val(pmd) & _PAGE_HUGE) != 0) #define pud_leaf(pud) ((pud_val(pud) & _PAGE_HUGE) != 0) +#define ARCH_WANTS_GENERIC_POPULATE_VMEMMAP_PTE + /* * We provide our own get_unmapped area to cope with the virtual aliasing * constraints placed on us by the cache architecture. diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h index 4c8fc6845503..6cfae7720882 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -1165,6 +1165,8 @@ static inline pud_t pud_modify(pud_t pud, pgprot_t newprot) #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ +#define ARCH_WANTS_GENERIC_POPULATE_VMEMMAP_PTE + /* * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that * are !pte_none() && !pte_present(). diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index ef0252a09c28..f60c09cdf1ec 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1368,6 +1368,8 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, } #endif +#define ARCH_WANTS_GENERIC_POPULATE_VMEMMAP_PTE + #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD static inline pud_t pudp_establish(struct vm_area_struct *vma, unsigned long address, pud_t *pudp, pud_t pud) diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 780fe849ff8b..59ab7ca93548 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -457,6 +457,28 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr, #endif #define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1) +#ifdef ARCH_WANTS_GENERIC_POPULATE_VMEMMAP_PTE +/* + * try_update_vmemmap_pte - Remap PTEs used by the vmemmap. + * @addr: Base address of the remapped PTE. + * @ptep: Page table pointer to be overwritten. + * @pte: Page table entry to write. + * + * This function is only to be used to update PTEs that map the vmemmap. The + * only valid transitions supported by this function are: leaf-level + * (PAGE_SIZE), valid-to-valid. The pfn and prot bits may be changed. + * + * Implementations of this function must ensure that, while the update is taking + * place, CPUs will not fault on the remapped virtual address. + */ +static inline int try_update_vmemmap_pte(unsigned long addr, pte_t *ptep, + pte_t pte) +{ + set_pte(ptep, pte); + return 0; +} +#endif + #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS extern int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address, pte_t *ptep, diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index 90db4d069ff6..3fdb1e4ce1a1 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -33,7 +33,7 @@ * operations. */ struct vmemmap_remap_walk { - void (*remap_pte)(pte_t *pte, unsigned long addr, + int (*remap_pte)(pte_t *pte, unsigned long addr, struct vmemmap_remap_walk *walk); unsigned long nr_walked; @@ -140,11 +140,13 @@ static int vmemmap_pte_entry(pte_t *pte, unsigned long addr, unsigned long next, struct mm_walk *walk) { struct vmemmap_remap_walk *vmemmap_walk = walk->private; + int ret = 0; - vmemmap_walk->remap_pte(pte, addr, vmemmap_walk); - vmemmap_walk->nr_walked++; + ret = vmemmap_walk->remap_pte(pte, addr, vmemmap_walk); + if (!ret) + vmemmap_walk->nr_walked++; - return 0; + return ret; } static const struct mm_walk_ops vmemmap_remap_ops = { @@ -196,18 +198,20 @@ static void free_vmemmap_page_list(struct list_head *list) free_vmemmap_page(page); } -static void vmemmap_remap_pte(pte_t *pte, unsigned long addr, - struct vmemmap_remap_walk *walk) +static int vmemmap_remap_pte(pte_t *pte, unsigned long addr, + struct vmemmap_remap_walk *walk) { struct page *page = pte_page(ptep_get(pte)); pte_t entry; + bool head; + int ret; + + head = walk->nr_walked == 0 && walk->vmemmap_head; /* Remapping the head page requires r/w */ - if (unlikely(walk->nr_walked == 0 && walk->vmemmap_head)) { + if (unlikely(head)) { VM_WARN_ON_ONCE(!PageHead((const struct page *)addr)); - list_del(&walk->vmemmap_head->lru); - /* * Makes sure that preceding stores to the page contents from * vmemmap_remap_free() become visible before the set_pte_at() @@ -226,17 +230,30 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr, entry = mk_pte(walk->vmemmap_tail, PAGE_KERNEL_RO); } + ret = try_update_vmemmap_pte(addr, pte, entry); + if (ret) + return ret; + + /* We successfully overwrote the vmemmap PTE, so we can free + * the vmemmap page that was just unmapped, and if we mapped + * the new head page, remove it from the list so that it + * doesn't get freed later. + */ list_add(&page->lru, walk->vmemmap_pages); - set_pte_at(&init_mm, addr, pte, entry); + if (head) + list_del(&walk->vmemmap_head->lru); + + return 0; } -static void vmemmap_restore_pte(pte_t *pte, unsigned long addr, - struct vmemmap_remap_walk *walk) +static int vmemmap_restore_pte(pte_t *pte, unsigned long addr, + struct vmemmap_remap_walk *walk) { struct page *src = pte_page(ptep_get(pte)), *dst; + int ret; if (WARN_ON_ONCE(!walk->vmemmap_tail)) - return; + return -EINVAL; /* * When restoring a partially-HVOed page, keep the copied head page @@ -244,20 +261,25 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr, * page. */ if (walk->vmemmap_tail != src) - return; + return 0; VM_WARN_ON_ONCE(PageHead((const struct page *)addr)); dst = list_first_entry(walk->vmemmap_pages, struct page, lru); - list_del(&dst->lru); copy_page(page_to_virt(dst), page_to_virt(src)); /* * Makes sure that preceding stores to the page contents become visible - * before the set_pte_at() write. + * before the try_update_vmemmap_pte() write. */ smp_wmb(); - set_pte_at(&init_mm, addr, pte, mk_pte(dst, PAGE_KERNEL)); + + ret = try_update_vmemmap_pte(addr, pte, mk_pte(dst, PAGE_KERNEL)); + if (ret) + return ret; + + list_del(&dst->lru); + return 0; } /** -- 2.56.0.rc1.315.gc6ed9934b7-goog