[4/4] userfaultfd: change the direction for UFFDIO_REMAP to out
diff mbox series

Message ID ab1b6be85254e111935104cf4a2293ab2fa4a8d6.1547251023.git.blake.caldwell@colorado.edu
State New
Headers show
Series
  • RFC: userfaultfd remap
Related show

Commit Message

Blake Caldwell Jan. 12, 2019, 12:36 a.m. UTC
Moving a page out of a userfaultfd registered region and into a userland
anonymous vma is needed by the use case of uncooperatively limiting the
resident size of the userfaultfd region. Reverse the direction of the
original userfaultfd_remap() to the out direction. Now after memory has
been removed, subsequent accesses will generate uffdio page fault events.

Signed-off-by: Blake Caldwell <blake.caldwell@colorado.edu>
---
 Documentation/admin-guide/mm/userfaultfd.rst | 10 ++++++++++
 fs/userfaultfd.c                             |  6 +++---
 2 files changed, 13 insertions(+), 3 deletions(-)

Comments

Mike Rapoport Jan. 20, 2019, 9:07 p.m. UTC | #1
Hi,

On Sat, Jan 12, 2019 at 12:36:29AM +0000, Blake Caldwell wrote:
> Moving a page out of a userfaultfd registered region and into a userland
> anonymous vma is needed by the use case of uncooperatively limiting the
> resident size of the userfaultfd region. Reverse the direction of the
> original userfaultfd_remap() to the out direction. Now after memory has
> been removed, subsequent accesses will generate uffdio page fault events.

It took me a while but better late then never :)

Why did you keep this as a separate patch? If the primary use case for
UFFDIO_REMAP to move pages out of userfaultfd region, why not make it so
from the beginning?

> Signed-off-by: Blake Caldwell <blake.caldwell@colorado.edu>
> ---
>  Documentation/admin-guide/mm/userfaultfd.rst | 10 ++++++++++
>  fs/userfaultfd.c                             |  6 +++---
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
> index 5048cf6..714af49 100644
> --- a/Documentation/admin-guide/mm/userfaultfd.rst
> +++ b/Documentation/admin-guide/mm/userfaultfd.rst
> @@ -108,6 +108,16 @@ UFFDIO_COPY. They're atomic as in guaranteeing that nothing can see an
>  half copied page since it'll keep userfaulting until the copy has
>  finished.
> 
> +To move pages out of a userfault registered region and into a user vma
> +the UFFDIO_REMAP ioctl can be used. This is only possible for the
> +"OUT" direction. For the "IN" direction, UFFDIO_COPY is preferred
> +since UFFDIO_REMAP requires a TLB flush on the source range at a
> +greater penalty than copying the page. With
> +UFFDIO_REGISTER_MODE_MISSING set, subsequent accesses to the same
> +region will generate a page fault event. This allows non-cooperative
> +removal of memory in a userfaultfd registered vma, effectively
> +limiting the amount of resident memory in such a region.
> +
>  QEMU/KVM
>  ========
> 
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index cf68cdb..8099da2 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1808,10 +1808,10 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx,
>  			   sizeof(uffdio_remap)-sizeof(__s64)))
>  		goto out;
> 
> -	ret = validate_range(ctx->mm, uffdio_remap.dst, uffdio_remap.len);
> +	ret = validate_range(current->mm, uffdio_remap.dst, uffdio_remap.len);
>  	if (ret)
>  		goto out;
> -	ret = validate_range(current->mm, uffdio_remap.src, uffdio_remap.len);
> +	ret = validate_range(ctx->mm, uffdio_remap.src, uffdio_remap.len);
>  	if (ret)
>  		goto out;
>  	ret = -EINVAL;
> @@ -1819,7 +1819,7 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx,
>  				  UFFDIO_REMAP_MODE_DONTWAKE))
>  		goto out;
> 
> -	ret = remap_pages(ctx->mm, current->mm,
> +	ret = remap_pages(current->mm, ctx->mm,
>  			  uffdio_remap.dst, uffdio_remap.src,
>  			  uffdio_remap.len, uffdio_remap.mode);
>  	if (unlikely(put_user(ret, &user_uffdio_remap->remap)))
> -- 
> 1.8.3.1
>
Blake Caldwell Jan. 24, 2019, 11:36 p.m. UTC | #2
> On Jan 20, 2019, at 4:07 PM, Mike Rapoport <rppt@linux.ibm.com> wrote:
> 
> Hi,
> 
> On Sat, Jan 12, 2019 at 12:36:29AM +0000, Blake Caldwell wrote:
>> Moving a page out of a userfaultfd registered region and into a userland
>> anonymous vma is needed by the use case of uncooperatively limiting the
>> resident size of the userfaultfd region. Reverse the direction of the
>> original userfaultfd_remap() to the out direction. Now after memory has
>> been removed, subsequent accesses will generate uffdio page fault events.
> 
> It took me a while but better late then never :)
> 
> Why did you keep this as a separate patch? If the primary use case for
> UFFDIO_REMAP to move pages out of userfaultfd region, why not make it so
> from the beginning?

Only to show what has changed since this was last proposed, but yes, that
change to fs/userfaultfd.c should be squashed with patch 3. The purpose of
patch 4 will only be documenting UFFDIO_REMAP.

I will make those changes for the next revision. Thanks for looking this over.

> 
>> Signed-off-by: Blake Caldwell <blake.caldwell@colorado.edu>
>> ---
>> Documentation/admin-guide/mm/userfaultfd.rst | 10 ++++++++++
>> fs/userfaultfd.c                             |  6 +++---
>> 2 files changed, 13 insertions(+), 3 deletions(-)
>> 
>> diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
>> index 5048cf6..714af49 100644
>> --- a/Documentation/admin-guide/mm/userfaultfd.rst
>> +++ b/Documentation/admin-guide/mm/userfaultfd.rst
>> @@ -108,6 +108,16 @@ UFFDIO_COPY. They're atomic as in guaranteeing that nothing can see an
>> half copied page since it'll keep userfaulting until the copy has
>> finished.
>> 
>> +To move pages out of a userfault registered region and into a user vma
>> +the UFFDIO_REMAP ioctl can be used. This is only possible for the
>> +"OUT" direction. For the "IN" direction, UFFDIO_COPY is preferred
>> +since UFFDIO_REMAP requires a TLB flush on the source range at a
>> +greater penalty than copying the page. With
>> +UFFDIO_REGISTER_MODE_MISSING set, subsequent accesses to the same
>> +region will generate a page fault event. This allows non-cooperative
>> +removal of memory in a userfaultfd registered vma, effectively
>> +limiting the amount of resident memory in such a region.
>> +
>> QEMU/KVM
>> ========
>> 
>> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
>> index cf68cdb..8099da2 100644
>> --- a/fs/userfaultfd.c
>> +++ b/fs/userfaultfd.c
>> @@ -1808,10 +1808,10 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx,
>> 			   sizeof(uffdio_remap)-sizeof(__s64)))
>> 		goto out;
>> 
>> -	ret = validate_range(ctx->mm, uffdio_remap.dst, uffdio_remap.len);
>> +	ret = validate_range(current->mm, uffdio_remap.dst, uffdio_remap.len);
>> 	if (ret)
>> 		goto out;
>> -	ret = validate_range(current->mm, uffdio_remap.src, uffdio_remap.len);
>> +	ret = validate_range(ctx->mm, uffdio_remap.src, uffdio_remap.len);
>> 	if (ret)
>> 		goto out;
>> 	ret = -EINVAL;
>> @@ -1819,7 +1819,7 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx,
>> 				  UFFDIO_REMAP_MODE_DONTWAKE))
>> 		goto out;
>> 
>> -	ret = remap_pages(ctx->mm, current->mm,
>> +	ret = remap_pages(current->mm, ctx->mm,
>> 			  uffdio_remap.dst, uffdio_remap.src,
>> 			  uffdio_remap.len, uffdio_remap.mode);
>> 	if (unlikely(put_user(ret, &user_uffdio_remap->remap)))
>> -- 
>> 1.8.3.1
>> 
> 
> -- 
> Sincerely yours,
> Mike.
<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 20, 2019, at 4:07 PM, Mike Rapoport &lt;<a href="mailto:rppt@linux.ibm.com" class="">rppt@linux.ibm.com</a>&gt; wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Hi,</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">On Sat, Jan 12, 2019 at 12:36:29AM +0000, Blake Caldwell wrote:</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none;" class="">Moving a page out of a userfaultfd registered region and into a userland<br class="">anonymous vma is needed by the use case of uncooperatively limiting the<br class="">resident size of the userfaultfd region. Reverse the direction of the<br class="">original userfaultfd_remap() to the out direction. Now after memory has<br class="">been removed, subsequent accesses will generate uffdio page fault events.<br class=""></blockquote><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">It took me a while but better late then never :)</span></div></blockquote><blockquote type="cite" class=""><div class=""><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Why did you keep this as a separate patch? If the primary use case for</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">UFFDIO_REMAP to move pages out of userfaultfd region, why not make it so</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">from the beginning?</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""></div></blockquote><div><br class=""></div>Only to show what has changed since this was last proposed, but yes, that</div><div>change to fs/userfaultfd.c should be squashed with patch 3. The purpose of</div><div>patch 4 will only be documenting UFFDIO_REMAP.</div><div><br class=""></div><div>I will make those changes for the next revision. Thanks for looking this over.</div><div><br class=""><blockquote type="cite" class=""><div class=""><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none;" class="">Signed-off-by: Blake Caldwell &lt;<a href="mailto:blake.caldwell@colorado.edu" class="">blake.caldwell@colorado.edu</a>&gt;<br class="">---<br class="">Documentation/admin-guide/mm/userfaultfd.rst | 10 ++++++++++<br class="">fs/userfaultfd.c &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;| &nbsp;6 +++---<br class="">2 files changed, 13 insertions(+), 3 deletions(-)<br class=""><br class="">diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst<br class="">index 5048cf6..714af49 100644<br class="">--- a/Documentation/admin-guide/mm/userfaultfd.rst<br class="">+++ b/Documentation/admin-guide/mm/userfaultfd.rst<br class="">@@ -108,6 +108,16 @@ UFFDIO_COPY. They're atomic as in guaranteeing that nothing can see an<br class="">half copied page since it'll keep userfaulting until the copy has<br class="">finished.<br class=""><br class="">+To move pages out of a userfault registered region and into a user vma<br class="">+the UFFDIO_REMAP ioctl can be used. This is only possible for the<br class="">+"OUT" direction. For the "IN" direction, UFFDIO_COPY is preferred<br class="">+since UFFDIO_REMAP requires a TLB flush on the source range at a<br class="">+greater penalty than copying the page. With<br class="">+UFFDIO_REGISTER_MODE_MISSING set, subsequent accesses to the same<br class="">+region will generate a page fault event. This allows non-cooperative<br class="">+removal of memory in a userfaultfd registered vma, effectively<br class="">+limiting the amount of resident memory in such a region.<br class="">+<br class="">QEMU/KVM<br class="">========<br class=""><br class="">diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c<br class="">index cf68cdb..8099da2 100644<br class="">--- a/fs/userfaultfd.c<br class="">+++ b/fs/userfaultfd.c<br class="">@@ -1808,10 +1808,10 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx,<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-converted-space">&nbsp;</span>&nbsp;&nbsp;sizeof(uffdio_remap)-sizeof(__s64)))<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span>goto out;<br class=""><br class="">-<span class="Apple-tab-span" style="white-space: pre;">	</span>ret = validate_range(ctx-&gt;mm, uffdio_remap.dst, uffdio_remap.len);<br class="">+<span class="Apple-tab-span" style="white-space: pre;">	</span>ret = validate_range(current-&gt;mm, uffdio_remap.dst, uffdio_remap.len);<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span>if (ret)<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span>goto out;<br class="">-<span class="Apple-tab-span" style="white-space: pre;">	</span>ret = validate_range(current-&gt;mm, uffdio_remap.src, uffdio_remap.len);<br class="">+<span class="Apple-tab-span" style="white-space: pre;">	</span>ret = validate_range(ctx-&gt;mm, uffdio_remap.src, uffdio_remap.len);<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span>if (ret)<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span>goto out;<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span>ret = -EINVAL;<br class="">@@ -1819,7 +1819,7 @@ static int userfaultfd_remap(struct userfaultfd_ctx *ctx,<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-converted-space">&nbsp;</span>&nbsp;UFFDIO_REMAP_MODE_DONTWAKE))<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span>goto out;<br class=""><br class="">-<span class="Apple-tab-span" style="white-space: pre;">	</span>ret = remap_pages(ctx-&gt;mm, current-&gt;mm,<br class="">+<span class="Apple-tab-span" style="white-space: pre;">	</span>ret = remap_pages(current-&gt;mm, ctx-&gt;mm,<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-converted-space">&nbsp;</span>&nbsp;uffdio_remap.dst, uffdio_remap.src,<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-tab-span" style="white-space: pre;">	</span><span class="Apple-converted-space">&nbsp;</span>&nbsp;uffdio_remap.len, uffdio_remap.mode);<br class=""><span class="Apple-tab-span" style="white-space: pre;">	</span>if (unlikely(put_user(ret, &amp;user_uffdio_remap-&gt;remap)))<br class="">--<span class="Apple-converted-space">&nbsp;</span><br class="">1.8.3.1<br class=""><br class=""></blockquote><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">--<span class="Apple-converted-space">&nbsp;</span></span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Sincerely yours,</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Mike.</span></div></blockquote></div><br class=""></body></html>

Patch
diff mbox series

diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 5048cf6..714af49 100644
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst
@@ -108,6 +108,16 @@  UFFDIO_COPY. They're atomic as in guaranteeing that nothing can see an
 half copied page since it'll keep userfaulting until the copy has
 finished.
 
+To move pages out of a userfault registered region and into a user vma
+the UFFDIO_REMAP ioctl can be used. This is only possible for the
+"OUT" direction. For the "IN" direction, UFFDIO_COPY is preferred
+since UFFDIO_REMAP requires a TLB flush on the source range at a
+greater penalty than copying the page. With
+UFFDIO_REGISTER_MODE_MISSING set, subsequent accesses to the same
+region will generate a page fault event. This allows non-cooperative
+removal of memory in a userfaultfd registered vma, effectively
+limiting the amount of resident memory in such a region.
+
 QEMU/KVM
 ========
 
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index cf68cdb..8099da2 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1808,10 +1808,10 @@  static int userfaultfd_remap(struct userfaultfd_ctx *ctx,
 			   sizeof(uffdio_remap)-sizeof(__s64)))
 		goto out;
 
-	ret = validate_range(ctx->mm, uffdio_remap.dst, uffdio_remap.len);
+	ret = validate_range(current->mm, uffdio_remap.dst, uffdio_remap.len);
 	if (ret)
 		goto out;
-	ret = validate_range(current->mm, uffdio_remap.src, uffdio_remap.len);
+	ret = validate_range(ctx->mm, uffdio_remap.src, uffdio_remap.len);
 	if (ret)
 		goto out;
 	ret = -EINVAL;
@@ -1819,7 +1819,7 @@  static int userfaultfd_remap(struct userfaultfd_ctx *ctx,
 				  UFFDIO_REMAP_MODE_DONTWAKE))
 		goto out;
 
-	ret = remap_pages(ctx->mm, current->mm,
+	ret = remap_pages(current->mm, ctx->mm,
 			  uffdio_remap.dst, uffdio_remap.src,
 			  uffdio_remap.len, uffdio_remap.mode);
 	if (unlikely(put_user(ret, &user_uffdio_remap->remap)))