Re: [PATCH v4 31/33] powerc/mm: try VMA lock-based page fault handling first

[Suren Baghdasaryan]

On Mon, Feb 27, 2023 at 9:37 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> From: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
>
> Attempt VMA lock-based page fault handling first, and fall back to the
> existing mmap_lock-based handling if that fails.
> Copied from "x86/mm: try VMA lock-based page fault handling first"

Hi Andrew,
Laurent posted a fix for this patch at
https://lore.kernel.org/all/20230306154244.17560-1-ldufour@xxxxxxxxxxxxx/.
Could you please squash the fix into this patch?
Thanks,
Suren.

>
> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
>  arch/powerpc/mm/fault.c                | 41 ++++++++++++++++++++++++++
>  arch/powerpc/platforms/powernv/Kconfig |  1 +
>  arch/powerpc/platforms/pseries/Kconfig |  1 +
>  3 files changed, 43 insertions(+)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 2bef19cc1b98..c7ae86b04b8a 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -469,6 +469,44 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
>         if (is_exec)
>                 flags |= FAULT_FLAG_INSTRUCTION;
>
> +#ifdef CONFIG_PER_VMA_LOCK
> +       if (!(flags & FAULT_FLAG_USER))
> +               goto lock_mmap;
> +
> +       vma = lock_vma_under_rcu(mm, address);
> +       if (!vma)
> +               goto lock_mmap;
> +
> +       if (unlikely(access_pkey_error(is_write, is_exec,
> +                                      (error_code & DSISR_KEYFAULT), vma))) {
> +               int rc = bad_access_pkey(regs, address, vma);
> +
> +               vma_end_read(vma);
> +               return rc;
> +       }
> +
> +       if (unlikely(access_error(is_write, is_exec, vma))) {
> +               int rc = bad_access(regs, address);
> +
> +               vma_end_read(vma);
> +               return rc;
> +       }
> +
> +       fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
> +       vma_end_read(vma);
> +
> +       if (!(fault & VM_FAULT_RETRY)) {
> +               count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
> +               goto done;
> +       }
> +       count_vm_vma_lock_event(VMA_LOCK_RETRY);
> +
> +       if (fault_signal_pending(fault, regs))
> +               return user_mode(regs) ? 0 : SIGBUS;
> +
> +lock_mmap:
> +#endif /* CONFIG_PER_VMA_LOCK */
> +
>         /* When running in the kernel we expect faults to occur only to
>          * addresses in user space.  All other faults represent errors in the
>          * kernel and should generate an OOPS.  Unfortunately, in the case of an
> @@ -545,6 +583,9 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
>
>         mmap_read_unlock(current->mm);
>
> +#ifdef CONFIG_PER_VMA_LOCK
> +done:
> +#endif
>         if (unlikely(fault & VM_FAULT_ERROR))
>                 return mm_fault_error(regs, address, fault);
>
> diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
> index ae248a161b43..70a46acc70d6 100644
> --- a/arch/powerpc/platforms/powernv/Kconfig
> +++ b/arch/powerpc/platforms/powernv/Kconfig
> @@ -16,6 +16,7 @@ config PPC_POWERNV
>         select PPC_DOORBELL
>         select MMU_NOTIFIER
>         select FORCE_SMP
> +       select ARCH_SUPPORTS_PER_VMA_LOCK
>         default y
>
>  config OPAL_PRD
> diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
> index b481c5c8bae1..9c205fe0e619 100644
> --- a/arch/powerpc/platforms/pseries/Kconfig
> +++ b/arch/powerpc/platforms/pseries/Kconfig
> @@ -21,6 +21,7 @@ config PPC_PSERIES
>         select HOTPLUG_CPU
>         select FORCE_SMP
>         select SWIOTLB
> +       select ARCH_SUPPORTS_PER_VMA_LOCK
>         default y
>
>  config PARAVIRT
> --
> 2.39.2.722.g9855ee24e9-goog
>