From: Ryan Roberts ryan.roberts@arm.com
mainline inclusion from mainline-v6.9-rc1 commit fb5451e5f72b31002760083a99fbb41771c4f1ad category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9CUEQ CVE: NA
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When core code iterates over a range of ptes and calls ptep_get() for each of them, if the range happens to cover contpte mappings, the number of pte reads becomes amplified by a factor of the number of PTEs in a contpte block. This is because for each call to ptep_get(), the implementation must read all of the ptes in the contpte block to which it belongs to gather the access and dirty bits.
This causes a hotspot for fork(), as well as operations that unmap memory such as munmap(), exit and madvise(MADV_DONTNEED). Fortunately we can fix this by implementing pte_batch_hint() which allows their iterators to skip getting the contpte tail ptes when gathering the batch of ptes to operate on. This results in the number of PTE reads returning to 1 per pte.
Link: https://lkml.kernel.org/r/20240215103205.2607016-17-ryan.roberts@arm.com Signed-off-by: Ryan Roberts ryan.roberts@arm.com Acked-by: Mark Rutland mark.rutland@arm.com Reviewed-by: David Hildenbrand david@redhat.com Tested-by: John Hubbard jhubbard@nvidia.com Acked-by: Catalin Marinas catalin.marinas@arm.com Cc: Alistair Popple apopple@nvidia.com Cc: Andrey Ryabinin ryabinin.a.a@gmail.com Cc: Ard Biesheuvel ardb@kernel.org Cc: Barry Song 21cnbao@gmail.com Cc: Borislav Petkov (AMD) bp@alien8.de Cc: Dave Hansen dave.hansen@linux.intel.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: James Morse james.morse@arm.com Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: Marc Zyngier maz@kernel.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Will Deacon will@kernel.org Cc: Yang Shi shy828301@gmail.com Cc: Zi Yan ziy@nvidia.com Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit fb5451e5f72b31002760083a99fbb41771c4f1ad) Signed-off-by: Kefeng Wang wangkefeng.wang@huawei.com --- arch/arm64/include/asm/pgtable.h | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index a8f1a35e3086..d759a20d2929 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1213,6 +1213,15 @@ static inline void contpte_try_unfold(struct mm_struct *mm, unsigned long addr, __contpte_try_unfold(mm, addr, ptep, pte); }
+#define pte_batch_hint pte_batch_hint +static inline unsigned int pte_batch_hint(pte_t *ptep, pte_t pte) +{ + if (!pte_valid_cont(pte)) + return 1; + + return CONT_PTES - (((unsigned long)ptep >> 3) & (CONT_PTES - 1)); +} + /* * The below functions constitute the public API that arm64 presents to the * core-mm to manipulate PTE entries within their page tables (or at least this