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    SubjectRe: [PATCH 3/4] arm64/mm: Consolidate page fault information capture
    On Wed, May 29, 2019 at 06:04:44PM +0530, Anshuman Khandual wrote:
    > This consolidates page fault information capture and move them bit earlier.
    > While here it also adds an wrapper is_write_abort(). It also saves some
    > cycles by replacing multiple user_mode() calls into a single one earlier
    > during the fault.

    To be honest, I doubt this has any measureable impact, but I agree that
    using variables _may_ make the flow control easier to understand.

    >
    > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
    > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Will Deacon <will.deacon@arm.com>
    > Cc: Mark Rutland <mark.rutland@arm.com>
    > Cc: James Morse <james.morse@arm.com>
    > Cc: Andrey Konovalov <andreyknvl@google.com>
    > ---
    > arch/arm64/mm/fault.c | 22 +++++++++++++++-------
    > 1 file changed, 15 insertions(+), 7 deletions(-)
    >
    > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
    > index da02678..170c71f 100644
    > --- a/arch/arm64/mm/fault.c
    > +++ b/arch/arm64/mm/fault.c
    > @@ -435,6 +435,11 @@ static bool is_el0_instruction_abort(unsigned int esr)
    > return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW;
    > }
    >
    > +static bool is_write_abort(unsigned int esr)
    > +{
    > + return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM);
    > +}

    In off-list review, I mentioned that this isn't true for EL1, and I
    think that we should name this 'is_el0_write_abort()' or add a comment
    explaining the caveats if factored into a helper.

    Thanks,
    Mark.

    > +
    > static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
    > struct pt_regs *regs)
    > {
    > @@ -443,6 +448,9 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
    > vm_fault_t fault, major = 0;
    > unsigned long vm_flags = VM_READ | VM_WRITE;
    > unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
    > + bool is_user = user_mode(regs);
    > + bool is_el0_exec = is_el0_instruction_abort(esr);
    > + bool is_write = is_write_abort(esr);
    >
    > if (notify_page_fault(regs, esr))
    > return 0;
    > @@ -454,12 +462,12 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
    > if (faulthandler_disabled() || !mm)
    > goto no_context;
    >
    > - if (user_mode(regs))
    > + if (is_user)
    > mm_flags |= FAULT_FLAG_USER;
    >
    > - if (is_el0_instruction_abort(esr)) {
    > + if (is_el0_exec) {
    > vm_flags = VM_EXEC;
    > - } else if ((esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM)) {
    > + } else if (is_write) {
    > vm_flags = VM_WRITE;
    > mm_flags |= FAULT_FLAG_WRITE;
    > }
    > @@ -487,7 +495,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
    > * we can bug out early if this is from code which shouldn't.
    > */
    > if (!down_read_trylock(&mm->mmap_sem)) {
    > - if (!user_mode(regs) && !search_exception_tables(regs->pc))
    > + if (!is_user && !search_exception_tables(regs->pc))
    > goto no_context;
    > retry:
    > down_read(&mm->mmap_sem);
    > @@ -498,7 +506,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
    > */
    > might_sleep();
    > #ifdef CONFIG_DEBUG_VM
    > - if (!user_mode(regs) && !search_exception_tables(regs->pc)) {
    > + if (!is_user && !search_exception_tables(regs->pc)) {
    > up_read(&mm->mmap_sem);
    > goto no_context;
    > }
    > @@ -516,7 +524,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
    > * in __lock_page_or_retry in mm/filemap.c.
    > */
    > if (fatal_signal_pending(current)) {
    > - if (!user_mode(regs))
    > + if (!is_user)
    > goto no_context;
    > return 0;
    > }
    > @@ -561,7 +569,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
    > * If we are in kernel mode at this point, we have no context to
    > * handle this fault with.
    > */
    > - if (!user_mode(regs))
    > + if (!is_user)
    > goto no_context;
    >
    > if (fault & VM_FAULT_OOM) {
    > --
    > 2.7.4
    >

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