[PATCH v2 14/20] hugetlb_vmemmap: Add fault injection for in-place vmemmap PTE updates
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WARM1d
From: James Houghton <hidden>
Date: 2026-10-03 00:22:09
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
Revision v2 of 2 in this series.
Revisions (2)
- v1 [diff vs current]
- v2 current
try_update_vmemmap_pte() may fail, e.g. on arm64 when the update keeps racing with hardware access flag updates. HVO handles such failures by rolling back the optimization, or by leaving folios partially optimized if the rollback or a later restore fails. These paths are rare to hit normally. Add a fault-injection capability, fail_hugetlb_vmemmap_pte, under CONFIG_FAIL_HUGETLB_VMEMMAP. When a fault is injected, the PTE update fails with -EAGAIN without touching the page tables, as if the in-place update had given up. It can be configured through debugfs or through the fail_hugetlb_vmemmap_pte= boot option, the latter allowing failures to be injected when optimizing bootmem folios. Assisted-by: LLM Signed-off-by: James Houghton <redacted> --- .../fault-injection/fault-injection.rst | 6 +++ lib/Kconfig.debug | 9 +++++ mm/hugetlb_vmemmap.c | 38 ++++++++++++++++++- 3 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentation/fault-injection/fault-injection.rst
index c2d3996b5b40..403206645fa4 100644
--- a/Documentation/fault-injection/fault-injection.rst
+++ b/Documentation/fault-injection/fault-injection.rst@@ -16,6 +16,11 @@ Available fault injection capabilities injects page allocation failures. (alloc_pages(), get_free_pages(), ...) +- fail_hugetlb_vmemmap_pte + + injects failures of the in-place vmemmap PTE remaps done by HugeTLB vmemmap + optimization. (try_update_vmemmap_pte()) + - fail_usercopy injects failures in user memory access functions. (copy_from_user(), get_user(), ...)
@@ -263,6 +268,7 @@ use the boot option:: failslab= fail_page_alloc= + fail_hugetlb_vmemmap_pte= fail_usercopy= fail_make_request= fail_futex=
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 134b15a44625..96cd1f1da94a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug@@ -2066,6 +2066,15 @@ config FAIL_PAGE_ALLOC help Provide fault-injection capability for alloc_pages(). +config FAIL_HUGETLB_VMEMMAP + bool "Fault-injection capability for HugeTLB vmemmap optimization" + depends on FAULT_INJECTION && HUGETLB_PAGE_OPTIMIZE_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. + config FAULT_INJECTION_USERCOPY bool "Fault injection capability for usercopy functions" depends on FAULT_INJECTION
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index fabf2b25fe59..1eca03a3def3 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c@@ -17,6 +17,7 @@ #include <linux/pgalloc.h> #include <linux/vmemmap-optimization.h> #include <linux/hugetlb.h> +#include <linux/fault-inject.h> #include <asm/tlbflush.h> #include "hugetlb_vmemmap.h"
@@ -50,6 +51,39 @@ struct vmemmap_remap_walk { unsigned long flags; }; +#ifdef CONFIG_FAIL_HUGETLB_VMEMMAP +static DECLARE_FAULT_ATTR(fail_hugetlb_vmemmap_pte); + +static int __init setup_fail_hugetlb_vmemmap_pte(char *str) +{ + return setup_fault_attr(&fail_hugetlb_vmemmap_pte, str); +} +__setup("fail_hugetlb_vmemmap_pte=", setup_fail_hugetlb_vmemmap_pte); + +#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); + return 0; +} +late_initcall(fail_hugetlb_vmemmap_debugfs); +#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */ + +/* + * Inject failures as if the in-place update lost a race too many times + * (see the arm64 implementations), without touching the page tables. + */ +static int hvo_update_vmemmap_pte(unsigned long addr, pte_t *ptep, pte_t pte) +{ + if (should_fail(&fail_hugetlb_vmemmap_pte, PAGE_SIZE)) + return -EAGAIN; + return try_update_vmemmap_pte(addr, ptep, pte); +} +#else +#define hvo_update_vmemmap_pte try_update_vmemmap_pte +#endif /* CONFIG_FAIL_HUGETLB_VMEMMAP */ + static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start, struct vmemmap_remap_walk *walk) {
@@ -235,7 +269,7 @@ static int 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); + ret = hvo_update_vmemmap_pte(addr, pte, entry); if (ret) return ret;
@@ -279,7 +313,7 @@ static int vmemmap_restore_pte(pte_t *pte, unsigned long addr, */ smp_wmb(); - ret = try_update_vmemmap_pte(addr, pte, mk_pte(dst, PAGE_KERNEL)); + ret = hvo_update_vmemmap_pte(addr, pte, mk_pte(dst, PAGE_KERNEL)); if (ret) return ret;
--
2.56.0.rc1.315.gc6ed9934b7-goog