2022-07-18 19:38:45

by Nadav Amit

Subject: [RFC PATCH 02/14] userfaultfd: try to map write-unprotected pages

From: Nadav Amit <[email protected]>

When using userfaultfd write-(un)protect ioctl, try to change the PTE to
be writable. This would save a page-fault afterwards.

Cc: Andrea Arcangeli <[email protected]>
Cc: Andrew Cooper <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yu Zhao <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
mm/userfaultfd.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index e0492f5f06a0..6013b217e9f3 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -799,6 +799,8 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
cp_flags = enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE;
if (uffd_flags & (UFFD_FLAGS_ACCESS_LIKELY|UFFD_FLAGS_WRITE_LIKELY))
cp_flags |= MM_CP_WILL_NEED;
+ if (!enable_wp && (uffd_flags & UFFD_FLAGS_WRITE_LIKELY))
+ cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;

tlb_gather_mmu(&tlb, dst_mm);
change_protection(&tlb, dst_vma, start, start + len, newprot, cp_flags);
--
2.25.1

2022-07-19 20:51:44

by Peter Xu

Subject: Re: [RFC PATCH 02/14] userfaultfd: try to map write-unprotected pages

On Mon, Jul 18, 2022 at 05:02:00AM -0700, Nadav Amit wrote:
> From: Nadav Amit <[email protected]>
>
> When using userfaultfd write-(un)protect ioctl, try to change the PTE to
> be writable. This would save a page-fault afterwards.
>
> Cc: Andrea Arcangeli <[email protected]>
> Cc: Andrew Cooper <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Andy Lutomirski <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Peter Xu <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Yu Zhao <[email protected]>
> Cc: Nick Piggin <[email protected]>
> Signed-off-by: Nadav Amit <[email protected]>

Acked-by: Peter Xu <[email protected]>

--
Peter Xu