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Fri, 02 Oct 2026 17:21:37 -0700 (PDT) Date: Sat, 3 Oct 2026 00:21:07 +0000 In-Reply-To: <20261003002123.505555-1-jthoughton@google.com> 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: <20261003002123.505555-5-jthoughton@google.com> Subject: [PATCH v2 04/20] hugetlb_vmemmap: Leave pages partially HVOed upon restore failure 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" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261002_172140_047965_9E439025 X-CRM114-Status: GOOD ( 21.82 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Right now it is assumed that the restore routine in vmemmap_remap_free() will not fail; that is, if we fail to fully optimize a folio, it is assumed that restoring the folio to its pre-HVO state is guaranteed to succeed. Although vmemmap restoration may never fail in practice, properly handle such failure cases now. This will leave folios in a partially HVOed state. In a follow-up patch, failure certainly becomes possible. In the event we end up with partially-HVOed folios, make sure to: 1. Leave the HVO page flag in place. 2. Free any unused vmemmap pages. Always pass the vmemmap_tail page to the restore routine to avoid leaking the non-optimized vmemmap pages for a partially HVOed page. Signed-off-by: James Houghton --- mm/hugetlb_vmemmap.c | 49 ++++++++++++++++++++++++++++++++++---------- 1 file changed, 38 insertions(+), 11 deletions(-) diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index 1a2645c382ba..90db4d069ff6 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -235,12 +235,15 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr, { struct page *src = pte_page(ptep_get(pte)), *dst; + if (WARN_ON_ONCE(!walk->vmemmap_tail)) + return; + /* - * When rolling back vmemmap_remap_free(), keep the copied head page + * When restoring a partially-HVOed page, keep the copied head page * mapping and restore only PTEs currently pointing at the shared tail * page. */ - if (walk->vmemmap_tail && walk->vmemmap_tail != src) + if (walk->vmemmap_tail != src) return; VM_WARN_ON_ONCE(PageHead((const struct page *)addr)); @@ -276,6 +279,7 @@ static int vmemmap_remap_split(unsigned long start, unsigned long end) return vmemmap_remap_range(start, end, &walk); } +#define VMEMMAP_REMAP_INCOMPLETE 1 /** * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end) * to use @vmemmap_head/tail, then free vmemmap which @@ -290,7 +294,8 @@ static int vmemmap_remap_split(unsigned long start, unsigned long end) * responsibility to free pages. * @flags: modifications to vmemmap_remap_walk flags * - * Return: %0 on success, negative error code otherwise. + * Return: %0 on success, VMEMMAP_REMAP_INCOMPLETE if the page is incompletely + * optimized, negative error code otherwise. */ static int vmemmap_remap_free(unsigned long start, unsigned long end, struct page *vmemmap_head, @@ -325,7 +330,8 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end, .flags = 0, }; - vmemmap_remap_range(start, end, &walk); + if (vmemmap_remap_range(start, end, &walk)) + return VMEMMAP_REMAP_INCOMPLETE; return ret; } @@ -358,6 +364,8 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end, * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end) * to the page which is from the @vmemmap_pages * respectively. + * @h: the hstate for the folio whose vmemmap is getting remapped + * @folio: the folio whose vmemmap is getting remapped * @start: start address of the vmemmap virtual address range that we want * to remap. * @end: end address of the vmemmap virtual address range that we want to @@ -366,20 +374,35 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end, * * Return: %0 on success, negative error code otherwise. */ -static int vmemmap_remap_alloc(unsigned long start, unsigned long end, +static int vmemmap_remap_alloc(const struct hstate *h, struct folio *folio, + unsigned long start, unsigned long end, unsigned long flags) { LIST_HEAD(vmemmap_pages); - struct vmemmap_remap_walk walk = { + struct vmemmap_remap_walk walk; + struct page *vmemmap_tail; + int ret; + + vmemmap_tail = vmemmap_shared_tail_page(h->order, folio_zone(folio)); + if (WARN_ON_ONCE(!vmemmap_tail)) + return -ENOMEM; + + if (alloc_vmemmap_page_list(start, end, &vmemmap_pages)) + return -ENOMEM; + + walk = (struct vmemmap_remap_walk) { .remap_pte = vmemmap_restore_pte, + .vmemmap_tail = vmemmap_tail, .vmemmap_pages = &vmemmap_pages, .flags = flags, }; - if (alloc_vmemmap_page_list(start, end, &vmemmap_pages)) - return -ENOMEM; + ret = vmemmap_remap_range(start, end, &walk); - return vmemmap_remap_range(start, end, &walk); + /* Not all pages may have been consumed */ + free_vmemmap_page_list(&vmemmap_pages); + + return ret; } static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON); @@ -412,7 +435,7 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h, * When a HugeTLB page is freed to the buddy allocator, previously * discarded vmemmap pages must be allocated and remapping. */ - ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, flags); + ret = vmemmap_remap_alloc(h, folio, vmemmap_start, vmemmap_end, flags); if (!ret) folio_clear_hugetlb_vmemmap_optimized(folio); @@ -545,7 +568,11 @@ static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h, vmemmap_head, vmemmap_tail, vmemmap_pages, flags); out: - if (ret) + /* + * If ret == VMEMMAP_REMAP_INCOMPLETE, the folio might be partially + * HVOed. Leave the HVO page folio flag in place. + */ + if (ret < 0) folio_clear_hugetlb_vmemmap_optimized(folio); return ret; -- 2.56.0.rc1.315.gc6ed9934b7-goog