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SubjectRe: [PATCH v9 23/24] x86/mm: Add speculative pagefault handling
On Tue, 13 Mar 2018, Laurent Dufour wrote:

> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index e6af2b464c3d..a73cf227edd6 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1239,6 +1239,9 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
> unsigned long address)
> {
> struct vm_area_struct *vma;
> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
> + struct vm_area_struct *spf_vma = NULL;
> +#endif
> struct task_struct *tsk;
> struct mm_struct *mm;
> int fault, major = 0;
> @@ -1332,6 +1335,27 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
> if (error_code & X86_PF_INSTR)
> flags |= FAULT_FLAG_INSTRUCTION;
>
> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
> + if ((error_code & X86_PF_USER) && (atomic_read(&mm->mm_users) > 1)) {
> + fault = handle_speculative_fault(mm, address, flags,
> + &spf_vma);
> +
> + if (!(fault & VM_FAULT_RETRY)) {
> + if (!(fault & VM_FAULT_ERROR)) {
> + perf_sw_event(PERF_COUNT_SW_SPF, 1,
> + regs, address);
> + goto done;
> + }
> + /*
> + * In case of error we need the pkey value, but
> + * can't get it from the spf_vma as it is only returned
> + * when VM_FAULT_RETRY is returned. So we have to
> + * retry the page fault with the mmap_sem grabbed.
> + */
> + }
> + }
> +#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */

All the comments from the powerpc version will apply here as well, the
only interesting point is whether VM_FAULT_FALLBACK can be returned from
handle_speculative_fault() to indicate its not possible.

> +
> /*
> * When running in the kernel we expect faults to occur only to
> * addresses in user space. All other faults represent errors in
> @@ -1365,7 +1389,16 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
> might_sleep();
> }
>
> - vma = find_vma(mm, address);
> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
> + if (spf_vma) {
> + if (can_reuse_spf_vma(spf_vma, address))
> + vma = spf_vma;
> + else
> + vma = find_vma(mm, address);
> + spf_vma = NULL;
> + } else
> +#endif
> + vma = find_vma(mm, address);
> if (unlikely(!vma)) {
> bad_area(regs, error_code, address);
> return;
> @@ -1451,6 +1484,9 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
> return;
> }
>
> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
> +done:
> +#endif
> /*
> * Major/minor page fault accounting. If any of the events
> * returned VM_FAULT_MAJOR, we account it as a major fault.

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