[PATCH] arm64: mm: Make flush_tlb_fix_spurious_fault() a no-op

Will Deacon
2020-09-30T13:19:07Z

Our use of broadcast TLB maintenance means that spurious page-faults
that have been handled already by another CPU do not require additional
TLB maintenance.

Make flush_tlb_fix_spurious_fault() a no-op and rely on the existing TLB
invalidation instead. Add an explicit flush_tlb_page() when making a page
dirty, as the TLB is permitted to cache the old read-only entry.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200728092220.GA21800@willie-the-truck
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/pgtable.h | 8 ++++++++
arch/arm64/mm/fault.c | 4 +++-
2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index bc68da9f5706..02ad3105c14c 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -50,6 +50,14 @@ extern void __pgd_error(const char *file, int line, unsigned long val);
__flush_tlb_range(vma, addr, end, PUD_SIZE, false, 1)
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

+/*
+ * Outside of a few very special situations (e.g. hibernation), we always
+ * use broadcast TLB invalidation instructions, therefore a spurious page
+ * fault on one CPU which has been handled concurrently by another CPU
+ * does not need to perform additional invalidation.
+ */
+#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
+
/*
* ZERO_PAGE is a global shared page that is always zero: used
* for zero-mapped memory areas etc..
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index f07333e86c2f..a696a7921da4 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -218,7 +218,9 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, pteval);
} while (pteval != old_pteval);

- flush_tlb_fix_spurious_fault(vma, address);
+ /* Invalidate a stale read-only entry */
+ if (dirty)
+ flush_tlb_page(vma, address);
return 1;
}

--
2.28.0.709.gb0816b6eb0-goog