On 08/18/2017 03:35 AM, Laurent Dufour wrote:
> This patch enable the speculative page fault on the PowerPC
> architecture.
>
> This will try a speculative page fault without holding the mmap_sem,
> if it returns with WM_FAULT_RETRY, the mmap_sem is acquired and the
s/WM_FAULT_RETRY/VM_FAULT_RETRY/
> traditional page fault processing is done.
>
> Support is only provide for BOOK3S_64 currently because:
> - require CONFIG_PPC_STD_MMU because checks done in
> set_access_flags_filter()
What checks are done in set_access_flags_filter() ? We are just
adding the code block in do_page_fault().
> - require BOOK3S because we can't support for book3e_hugetlb_preload()
> called by update_mmu_cache()
>
> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++
> arch/powerpc/mm/fault.c | 30 +++++++++++++++++++++++++++-
> 2 files changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 818a58fc3f4f..897f8b9f67e6 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -313,6 +313,11 @@ extern unsigned long pci_io_base;
> /* Advertise support for _PAGE_SPECIAL */
> #define __HAVE_ARCH_PTE_SPECIAL
>
> +/* Advertise that we call the Speculative Page Fault handler */
> +#if defined(CONFIG_PPC_BOOK3S_64)
> +#define __HAVE_ARCH_CALL_SPF
> +#endif
> +
> #ifndef __ASSEMBLY__
>
> /*
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 4c422632047b..7b3cc4c30eab 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -291,9 +291,36 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
> if (is_write && is_user)
> store_update_sp = store_updates_sp(regs);
>
> - if (is_user)
> + if (is_user) {
> flags |= FAULT_FLAG_USER;
>
> +#if defined(__HAVE_ARCH_CALL_SPF)
> + /* let's try a speculative page fault without grabbing the
> + * mmap_sem.
> + */
> +
> + /*
> + * flags is set later based on the VMA's flags, for the common
> + * speculative service, we need some flags to be set.
> + */
> + if (is_write)
> + flags |= FAULT_FLAG_WRITE;
> +
> + fault = handle_speculative_fault(mm, address, flags);
> + if (!(fault & VM_FAULT_RETRY || fault & VM_FAULT_ERROR)) {
> + perf_sw_event(PERF_COUNT_SW_SPF_DONE, 1,
> + regs, address);
> + goto done;
Why we should retry with classical page fault on VM_FAULT_ERROR ?
We should always return VM_FAULT_RETRY in case there is a clear
collision some where which requires retry with classical method
and return VM_FAULT_ERROR in cases where we know that it cannot
be retried and fail for good. Should not handle_speculative_fault()
be changed to accommodate this ?
> + }
> +
> + /*
> + * Resetting flags since the following code assumes
> + * FAULT_FLAG_WRITE is not set.
> + */
> + flags &= ~FAULT_FLAG_WRITE;
> +#endif /* defined(__HAVE_ARCH_CALL_SPF) */
Setting and resetting of FAULT_FLAG_WRITE seems confusing. Why you
say that some flags need to be set for handle_speculative_fault()
function. Could you elaborate on this ?
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