[PATCH 6.7 59/61] ARM: 9328/1: mm: try VMA lock-based page fault handling first

Sasha Levin
2024-03-13T16:34:13Z

From: Wang Kefeng <wangkefeng.wang@huawei.com>

[ Upstream commit c16af1212479570454752671a170a1756e11fdfb ]

Attempt VMA lock-based page fault handling first, and fall back to the
existing mmap_lock-based handling if that fails, the ebizzy benchmark
shows 25% improvement on qemu with 2 cpus.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Stable-dep-of: e870920bbe68 ("arch/arm/mm: fix major fault accounting when retrying under per-VMA lock")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm/Kconfig | 1 +
arch/arm/mm/fault.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 31 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index f8567e95f98be..8f47d6762ea4b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -35,6 +35,7 @@ config ARM
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
+ select ARCH_SUPPORTS_PER_VMA_LOCK
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_USE_MEMTEST
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index fef62e4a9edde..e96fb40b9cc32 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -278,6 +278,35 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)

perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);

+ if (!(flags & FAULT_FLAG_USER))
+ goto lock_mmap;
+
+ vma = lock_vma_under_rcu(mm, addr);
+ if (!vma)
+ goto lock_mmap;
+
+ if (!(vma->vm_flags & vm_flags)) {
+ vma_end_read(vma);
+ goto lock_mmap;
+ }
+ fault = handle_mm_fault(vma, addr, flags | FAULT_FLAG_VMA_LOCK, regs);
+ if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+ vma_end_read(vma);
+
+ if (!(fault & VM_FAULT_RETRY)) {
+ count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+ goto done;
+ }
+ count_vm_vma_lock_event(VMA_LOCK_RETRY);
+
+ /* Quick path to respond to signals */
+ if (fault_signal_pending(fault, regs)) {
+ if (!user_mode(regs))
+ goto no_context;
+ return 0;
+ }
+lock_mmap:
+
retry:
vma = lock_mm_and_find_vma(mm, addr, regs);
if (unlikely(!vma)) {
@@ -316,6 +345,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
}

mmap_read_unlock(mm);
+done:

/*
* Handle the "normal" case first - VM_FAULT_MAJOR
--
2.43.0