[PATCH v2 19/20 DO-NOT-MERGE] hugetlb_vmemmap: Add fault injection for in-place vmemmap PMD splits
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COOLING9d
From: James Houghton <hidden>
Date: 2026-10-03 00:22:19
Also in:
linux-mm, lkml
Subsystem:
documentation, fault injection support, hugetlb subsystem, library code, memory management, the rest · Maintainers:
Jonathan Corbet, Akinobu Mita, Muchun Song, Oscar Salvador, Andrew Morton, Linus Torvalds
Like try_update_vmemmap_pte(), try_populate_vmemmap_pmd() may fail, e.g. on arm64 when replacing the block mapping keeps racing with hardware access flag updates. HVO handles such failures by not optimizing the folio. Add a fault-injection capability, fail_hugetlb_vmemmap_pmd, alongside fail_hugetlb_vmemmap_pte. When a fault is injected, the PMD split fails with -EAGAIN without touching the page tables. It can be configured through debugfs or through the fail_hugetlb_vmemmap_pmd= boot option. Since vmemmap PMDs are only split once, the boot option is the most effective way to exercise this path. Assisted-by: LLM Signed-off-by: James Houghton <redacted> --- .../fault-injection/fault-injection.rst | 8 +++++--- lib/Kconfig.debug | 4 ++-- mm/hugetlb_vmemmap.c | 20 ++++++++++++++++++- 3 files changed, 26 insertions(+), 6 deletions(-)
diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentation/fault-injection/fault-injection.rst
index 403206645fa4..5cfabea811da 100644
--- a/Documentation/fault-injection/fault-injection.rst
+++ b/Documentation/fault-injection/fault-injection.rst@@ -16,10 +16,11 @@ Available fault injection capabilities injects page allocation failures. (alloc_pages(), get_free_pages(), ...) -- fail_hugetlb_vmemmap_pte +- fail_hugetlb_vmemmap_pte, fail_hugetlb_vmemmap_pmd - injects failures of the in-place vmemmap PTE remaps done by HugeTLB vmemmap - optimization. (try_update_vmemmap_pte()) + injects failures of the in-place vmemmap PTE remaps and PMD splits done by + HugeTLB vmemmap optimization. (try_update_vmemmap_pte(), + try_populate_vmemmap_pmd()) - fail_usercopy
@@ -269,6 +270,7 @@ use the boot option:: failslab= fail_page_alloc= fail_hugetlb_vmemmap_pte= + fail_hugetlb_vmemmap_pmd= fail_usercopy= fail_make_request= fail_futex=
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 96cd1f1da94a..7abda377c737 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug@@ -2072,8 +2072,8 @@ config FAIL_HUGETLB_VMEMMAP help Provide fault-injection capability for the in-place vmemmap page table updates done by HugeTLB vmemmap optimization (HVO), i.e. - try_update_vmemmap_pte(). This exercises the rollback and - partially-optimized folio paths. + try_update_vmemmap_pte() and try_populate_vmemmap_pmd(). This + exercises the rollback and partially-optimized folio paths. config FAULT_INJECTION_USERCOPY bool "Fault injection capability for usercopy functions"
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 9e0f52474bdb..f50880dd79a2 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c@@ -53,6 +53,7 @@ struct vmemmap_remap_walk { #ifdef CONFIG_FAIL_HUGETLB_VMEMMAP static DECLARE_FAULT_ATTR(fail_hugetlb_vmemmap_pte); +static DECLARE_FAULT_ATTR(fail_hugetlb_vmemmap_pmd); static int __init setup_fail_hugetlb_vmemmap_pte(char *str) {
@@ -60,11 +61,19 @@ static int __init setup_fail_hugetlb_vmemmap_pte(char *str) } __setup("fail_hugetlb_vmemmap_pte=", setup_fail_hugetlb_vmemmap_pte); +static int __init setup_fail_hugetlb_vmemmap_pmd(char *str) +{ + return setup_fault_attr(&fail_hugetlb_vmemmap_pmd, str); +} +__setup("fail_hugetlb_vmemmap_pmd=", setup_fail_hugetlb_vmemmap_pmd); + #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS static int __init fail_hugetlb_vmemmap_debugfs(void) { fault_create_debugfs_attr("fail_hugetlb_vmemmap_pte", NULL, &fail_hugetlb_vmemmap_pte); + fault_create_debugfs_attr("fail_hugetlb_vmemmap_pmd", NULL, + &fail_hugetlb_vmemmap_pmd); return 0; } late_initcall(fail_hugetlb_vmemmap_debugfs);
@@ -80,8 +89,17 @@ static int hvo_update_vmemmap_pte(unsigned long addr, pte_t *ptep, pte_t pte) return -EAGAIN; return try_update_vmemmap_pte(addr, ptep, pte); } + +static int hvo_populate_vmemmap_pmd(unsigned long addr, pmd_t *pmdp, + pte_t *pgtable) +{ + if (should_fail(&fail_hugetlb_vmemmap_pmd, PMD_SIZE)) + return -EAGAIN; + return try_populate_vmemmap_pmd(addr, pmdp, pgtable); +} #else #define hvo_update_vmemmap_pte try_update_vmemmap_pte +#define hvo_populate_vmemmap_pmd try_populate_vmemmap_pmd #endif /* CONFIG_FAIL_HUGETLB_VMEMMAP */ static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start,
@@ -113,7 +131,7 @@ static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start, if (likely(pmd_leaf(*pmd))) { /* Make pte visible before pmd. See comment in pmd_install(). */ smp_wmb(); - ret = try_populate_vmemmap_pmd(start, pmd, pgtable); + ret = hvo_populate_vmemmap_pmd(start, pmd, pgtable); if (ret) goto free;
--
2.56.0.rc1.315.gc6ed9934b7-goog