[PATCH] LoongArch: mm: try VMA lock-based page fault handling first

[Wentao Guan <guanwentao@uniontech.com>]

Attempt VMA lock-based page fault handling first, and fall back to the
existing mmap_lock-based handling if that fails.

The "ebizzy -mTRp" on 3A6000 shows that PER_VMA_LOCK can
improve the benchmark by about 20.7%.

This is the loongarch variant of "x86/mm: try VMA lock-based page fault
handling first".

Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
ebizzy-0.3(can download by phoronix-test-suite):
before patch:
97800 records/s
real 10.00 s user  0.25 s sys  13.54 s
97835 records/s
real 10.00 s user  0.27 s sys  13.51 s
97929 records/s
real 10.00 s user  0.26 s sys  13.53 s
97736 records/s
real 10.00 s user  0.31 s sys  13.48 s
97914 records/s
real 10.00 s user  0.30 s sys  13.50 s
97916 records/s
real 10.00 s user  0.31 s sys  13.48 s
97857 records/s
real 10.00 s user  0.28 s sys  13.51 s
97927 records/s
real 10.00 s user  0.24 s sys  13.55 s
97962 records/s
real 10.00 s user  0.41 s sys  13.39 s
97501 records/s
real 10.00 s user  0.20 s sys  13.53 s
after patch:
117645 records/s
real 10.00 s user  0.31 s sys  23.17 s
118207 records/s
real 10.00 s user  0.37 s sys  23.18 s
118426 records/s
real 10.00 s user  0.32 s sys  23.14 s
118172 records/s
real 10.00 s user  0.44 s sys  23.07 s
118548 records/s
real 10.00 s user  0.45 s sys  23.04 s
118011 records/s
real 10.00 s user  0.32 s sys  23.15 s
118143 records/s
real 10.00 s user  0.41 s sys  23.09 s
118181 records/s
real 10.00 s user  0.42 s sys  23.12 s
117721 records/s
real 10.00 s user  0.34 s sys  23.17 s
118138 records/s
real 10.00 s user  0.42 s sys  23.04 s
---
---
 arch/loongarch/Kconfig    |  1 +
 arch/loongarch/mm/fault.c | 49 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 0631a6b11281b..1c517954157c0 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -69,6 +69,7 @@ config LOONGARCH
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
 	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
 	select ARCH_SUPPORTS_NUMA_BALANCING
+	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_SUPPORTS_RT
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF
diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
index deefd9617d008..d2dc3e194dd76 100644
--- a/arch/loongarch/mm/fault.c
+++ b/arch/loongarch/mm/fault.c
@@ -215,6 +215,53 @@ static void __kprobes __do_page_fault(struct pt_regs *regs,
 		flags |= FAULT_FLAG_USER;
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
+	if (!(flags & FAULT_FLAG_USER))
+		goto lock_mmap;
+
+	vma = lock_vma_under_rcu(mm, address);
+	if (!vma)
+		goto lock_mmap;
+
+	if (write) {
+		flags |= FAULT_FLAG_WRITE;
+		if (!(vma->vm_flags & VM_WRITE)) {
+			vma_end_read(vma);
+			si_code = SEGV_ACCERR;
+			goto bad_area_nosemaphore;
+		}
+	} else {
+		if (!(vma->vm_flags & VM_EXEC) && address == exception_era(regs)){
+			vma_end_read(vma);
+			si_code = SEGV_ACCERR;
+			goto bad_area_nosemaphore;
+		}
+		if (!(vma->vm_flags & (VM_READ | VM_WRITE)) && address != exception_era(regs)){
+			vma_end_read(vma);
+			si_code = SEGV_ACCERR;
+			goto bad_area_nosemaphore;
+		}
+	}
+
+	fault = handle_mm_fault(vma, address, 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);
+	if (fault & VM_FAULT_MAJOR)
+		flags |= FAULT_FLAG_TRIED;
+
+	/* Quick path to respond to signals */
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
+			no_context(regs, write, address);
+		return;
+	}
+lock_mmap:
+
 retry:
 	vma = lock_mm_and_find_vma(mm, address, regs);
 	if (unlikely(!vma))
@@ -292,6 +339,8 @@ static void __kprobes __do_page_fault(struct pt_regs *regs,
 	}
 
 	mmap_read_unlock(mm);
+done:
+	return;	
 }
 
 asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
-- 
2.20.1