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SubjectRe: [PATCH] userfaultfd: clear flag if remap event not enabled
On Mon, Dec 10, 2018 at 02:51:21PM +0800, Peter Xu wrote:
> When the process being tracked do mremap() without
> UFFD_FEATURE_EVENT_REMAP on the corresponding tracking uffd file
> handle, we should not generate the remap event, and at the same
> time we should clear all the uffd flags on the new VMA. Without
> this patch, we can still have the VM_UFFD_MISSING|VM_UFFD_WP
> flags on the new VMA even the fault handling process does not
> even know the existance of the VMA.
>
> CC: Andrea Arcangeli <aarcange@redhat.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: Mike Rapoport <rppt@linux.vnet.ibm.com>
> CC: Kirill A. Shutemov <kirill@shutemov.name>
> CC: Hugh Dickins <hughd@google.com>
> CC: Pavel Emelyanov <xemul@virtuozzo.com>
> CC: Pravin Shedge <pravin.shedge4linux@gmail.com>
> CC: linux-mm@kvack.org
> CC: linux-kernel@vger.kernel.org
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> fs/userfaultfd.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index cd58939dc977..798ae8a438ff 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -740,6 +740,9 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
> vm_ctx->ctx = ctx;
> userfaultfd_ctx_get(ctx);
> WRITE_ONCE(ctx->mmap_changing, true);
> + } else if (ctx) {
> + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> + vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);

My preference would be

if (!ctx)
return;

if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
...
} else {
...
}

but I don't feel strongly about it.

I'd appreciate a comment in the code and with it

Acked-by: Mike Rapoport <rppt@linux.ibm.com>


> }
> }
>
> --
> 2.17.1
>

--
Sincerely yours,
Mike.

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