Re: [PATCH RFC v3 31/35] khugepaged: arm64: Don't collapse MTE enabled VMAs
From: Anshuman Khandual <hidden>
Date: 2024-02-01 08:12:28
Also in:
kvmarm, linux-arch, linux-arm-kernel, linux-fsdevel, linux-mm, lkml
On 1/25/24 22:12, Alexandru Elisei wrote:
copy_user_highpage() will do memory allocation if there are saved tags for
the destination page, and the page is missing tag storage.
After commit a349d72fd9ef ("mm/pgtable: add rcu_read_lock() and
rcu_read_unlock()s"), collapse_huge_page() calls
__collapse_huge_page_copy() -> .. -> copy_user_highpage() with the RCU lock
held, which means that copy_user_highpage() can only allocate memory using
GFP_ATOMIC or equivalent.
Get around this by refusing to collapse pages into a transparent huge page
if the VMA is MTE-enabled.Makes sense when copy_user_highpage() will allocate memory for tag storage.
Signed-off-by: Alexandru Elisei <redacted> --- Changes since rfc v2: * New patch. I think an agreement on whether copy*_user_highpage() should be always allowed to sleep, or should not be allowed, would be useful.
This is a good question ! Even after preventing the collapse of MTE VMA here, there still might be more paths where a sleeping (i.e memory allocating) copy*_user_highpage() becomes problematic ?
quoted hunk ↗ jump to hunk
arch/arm64/include/asm/pgtable.h | 3 +++ arch/arm64/kernel/mte_tag_storage.c | 5 +++++ include/linux/khugepaged.h | 5 +++++ mm/khugepaged.c | 4 ++++ 4 files changed, 17 insertions(+)diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 87ae59436162..d0473538c926 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h@@ -1120,6 +1120,9 @@ static inline bool arch_alloc_cma(gfp_t gfp_mask) return true; } +bool arch_hugepage_vma_revalidate(struct vm_area_struct *vma, unsigned long address); +#define arch_hugepage_vma_revalidate arch_hugepage_vma_revalidate + #endif /* CONFIG_ARM64_MTE_TAG_STORAGE */ #endif /* CONFIG_ARM64_MTE */diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c index ac7b9c9c585c..a99959b70573 100644 --- a/arch/arm64/kernel/mte_tag_storage.c +++ b/arch/arm64/kernel/mte_tag_storage.c@@ -636,3 +636,8 @@ void arch_alloc_page(struct page *page, int order, gfp_t gfp) if (tag_storage_enabled() && alloc_requires_tag_storage(gfp)) reserve_tag_storage(page, order, gfp); } + +bool arch_hugepage_vma_revalidate(struct vm_area_struct *vma, unsigned long address) +{ + return !(vma->vm_flags & VM_MTE); +}diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h index f68865e19b0b..461e4322dff2 100644 --- a/include/linux/khugepaged.h +++ b/include/linux/khugepaged.h@@ -38,6 +38,11 @@ static inline void khugepaged_exit(struct mm_struct *mm) if (test_bit(MMF_VM_HUGEPAGE, &mm->flags)) __khugepaged_exit(mm); } + +#ifndef arch_hugepage_vma_revalidate +#define arch_hugepage_vma_revalidate(vma, address) 1
Please replace s/1/true as arch_hugepage_vma_revalidate() returns bool ?
+#endif
Right, above construct is much better than __HAVE_ARCH_XXXX based one.
quoted hunk ↗ jump to hunk
+ #else /* CONFIG_TRANSPARENT_HUGEPAGE */ static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm) {diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 2b219acb528e..cb9a9ddb4d86 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c@@ -935,6 +935,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, */ if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap))) return SCAN_PAGE_ANON; + + if (!arch_hugepage_vma_revalidate(vma, address)) + return SCAN_VMA_CHECK; + return SCAN_SUCCEED; }
Otherwise this LGTM.