On 08/18/2017 03:35 AM, Laurent Dufour wrote:
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>
> Try a speculative fault before acquiring mmap_sem, if it returns with
> VM_FAULT_RETRY continue with the mmap_sem acquisition and do the
> traditional fault.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
>
> [Clearing of FAULT_FLAG_ALLOW_RETRY is now done in
> handle_speculative_fault()]
> [Retry with usual fault path in the case VM_ERROR is returned by
> handle_speculative_fault(). This allows signal to be delivered]
> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/pgtable_types.h | 7 +++++++
> arch/x86/mm/fault.c | 19 +++++++++++++++++++
> 2 files changed, 26 insertions(+)
>
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index bf9638e1ee42..4fd2693a037e 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -234,6 +234,13 @@ enum page_cache_mode {
> #define PGD_IDENT_ATTR 0x001 /* PRESENT (no other attributes) */
> #endif
>
> +/*
> + * Advertise that we call the Speculative Page Fault handler.
> + */
> +#ifdef CONFIG_X86_64
> +#define __HAVE_ARCH_CALL_SPF
> +#endif
> +
> #ifdef CONFIG_X86_32
> # include <asm/pgtable_32_types.h>
> #else
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 2a1fa10c6a98..4c070b9a4362 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1365,6 +1365,24 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
> if (error_code & PF_INSTR)
> flags |= FAULT_FLAG_INSTRUCTION;
>
> +#ifdef __HAVE_ARCH_CALL_SPF
> + if (error_code & PF_USER) {
> + fault = handle_speculative_fault(mm, address, flags);
> +
> + /*
> + * We also check against VM_FAULT_ERROR because we have to
> + * raise a signal by calling later mm_fault_error() which
> + * requires the vma pointer to be set. So in that case,
> + * we fall through the normal path.
Cant mm_fault_error() be called inside handle_speculative_fault() ?
Falling through the normal page fault path again just to raise a
signal seems overkill. Looking into mm_fault_error(), it seems they
are different for x86 and powerpc.
X86:
mm_fault_error(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma,
unsigned int fault)
powerpc:
mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault)
Even in case of X86, I guess we would have reference to the faulting
VMA (after the SRCU search) which can be used to call this function
directly.
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