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    Subject[PATCH v3 32/35] arm64/mm: try VMA lock-based page fault handling first
    From
    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 <surenb@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 c5ccca26a408..9f2c0e352da3 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 f4cb0f85ccf4..9e0db5c387e3 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))
    + 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 & PAGE_MASK,
    + mm_flags | FAULT_FLAG_VMA_LOCK, regs);
    + 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:
    +#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.
    */
    --
    2.39.1
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