2018-12-11 06:30:37

by Peter Xu

Subject: [PATCH v2] userfaultfd: clear flag if remap event not enabled

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 <[email protected]>
CC: Andrew Morton <[email protected]>
CC: Mike Rapoport <[email protected]>
CC: Kirill A. Shutemov <[email protected]>
CC: Hugh Dickins <[email protected]>
CC: Pavel Emelyanov <[email protected]>
CC: Pravin Shedge <[email protected]>
CC: [email protected]
CC: [email protected]
Acked-by: Mike Rapoport <[email protected]>
Reviewed-by: Andrea Arcangeli <[email protected]>
Signed-off-by: Peter Xu <[email protected]>
---
fs/userfaultfd.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index cd58939dc977..4567b5b6fd32 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -736,10 +736,18 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
struct userfaultfd_ctx *ctx;

ctx = vma->vm_userfaultfd_ctx.ctx;
- if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
+
+ if (!ctx)
+ return;
+
+ if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
vm_ctx->ctx = ctx;
userfaultfd_ctx_get(ctx);
WRITE_ONCE(ctx->mmap_changing, true);
+ } else {
+ /* Drop uffd context if remap feature not enabled */
+ vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
+ vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
}
}

--
2.17.1

2018-12-11 13:48:55

by William Kucharski

Subject: Re: [PATCH v2] userfaultfd: clear flag if remap event not enabled

> On Dec 10, 2018, at 10:34 PM, Peter Xu <[email protected]> wrote:
>
> ---
> fs/userfaultfd.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index cd58939dc977..4567b5b6fd32 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -736,10 +736,18 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
> struct userfaultfd_ctx *ctx;
>
> ctx = vma->vm_userfaultfd_ctx.ctx;
> - if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
> +
> + if (!ctx)
> + return;
> +
> + if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
> vm_ctx->ctx = ctx;
> userfaultfd_ctx_get(ctx);
> WRITE_ONCE(ctx->mmap_changing, true);
> + } else {
> + /* Drop uffd context if remap feature not enabled */
> + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> + vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
> }
> }
>
> --
> 2.17.1
>

Looks good.

Reviewed-by: William Kucharski <[email protected]>