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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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