[PATCH 35/41] arm64/mm: try VMA lock-based page fault handling first

[Suren Baghdasaryan]

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

Signed-off-by: Suren Baghdasaryan <sur...@google.com>
---
 arch/arm64/Kconfig    |  1 +
 arch/arm64/mm/fault.c | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 03934808b2ed..829fa6d14a36 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -95,6 +95,7 @@ config ARM64
        select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
        select ARCH_SUPPORTS_NUMA_BALANCING
        select ARCH_SUPPORTS_PAGE_TABLE_CHECK
+       select ARCH_SUPPORTS_PER_VMA_LOCK
        select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
        select ARCH_WANT_DEFAULT_BPF_JIT
        select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 596f46dabe4e..833fa8bab291 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -535,6 +535,9 @@ static int __kprobes do_page_fault(unsigned long far, 
unsigned long esr,
        unsigned long vm_flags;
        unsigned int mm_flags = FAULT_FLAG_DEFAULT;
        unsigned long addr = untagged_addr(far);
+#ifdef CONFIG_PER_VMA_LOCK
+       struct vm_area_struct *vma;
+#endif
 
        if (kprobe_page_fault(regs, esr))
                return 0;
@@ -585,6 +588,36 @@ static int __kprobes do_page_fault(unsigned long far, 
unsigned long esr,
 
        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 
+#ifdef CONFIG_PER_VMA_LOCK
+       if (!(mm_flags & FAULT_FLAG_USER) || atomic_read(&mm->mm_users) == 1)
+               goto lock_mmap;
+
+       vma = lock_vma_under_rcu(mm, addr);
+       if (!vma)
+               goto lock_mmap;
+
+       if (!(vma->vm_flags & vm_flags)) {
+               vma_read_unlock(vma);
+               goto lock_mmap;
+       }
+       fault = handle_mm_fault(vma, addr & PAGE_MASK,
+                               mm_flags | FAULT_FLAG_VMA_LOCK, regs);
+       vma_read_unlock(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:
+#endif /* CONFIG_PER_VMA_LOCK */
        /*
         * As per x86, we may deadlock here. However, since the kernel only
         * validly references user space from well defined areas of the code,
@@ -628,6 +661,9 @@ static int __kprobes do_page_fault(unsigned long far, 
unsigned long esr,
        }
        mmap_read_unlock(mm);
 
+#ifdef CONFIG_PER_VMA_LOCK
+done:
+#endif
        /*
         * Handle the "normal" (no error) case first.
         */
-- 
2.39.0