lkml.org 
[lkml]   [2017]   [Nov]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 4/6] hugetlbfs: implement memfd sealing
From
Date
On 11/03/2017 10:03 AM, David Herrmann wrote:
> Hi
>
> On Tue, Oct 31, 2017 at 7:40 PM, Marc-André Lureau
> <marcandre.lureau@redhat.com> wrote:
>> Implements memfd sealing, similar to shmem:
>> - WRITE: deny fallocate(PUNCH_HOLE). mmap() write is denied in
>> memfd_add_seals(). write() doesn't exist for hugetlbfs.
>> - SHRINK: added similar check as shmem_setattr()
>> - GROW: added similar check as shmem_setattr() & shmem_fallocate()
>>
>> Except write() operation that doesn't exist with hugetlbfs, that
>> should make sealing as close as it can be to shmem support.
>
> SEAL, SHRINK, and GROW look fine to me.
>
> Regarding WRITE

The commit message may not be clear. However, hugetlbfs does not support
the write system call (or aio). The only way to modify contents of a
hugetlbfs file is via mmap or hole punch/truncate. So, we do not really
need to worry about those special (a)io cases for hugetlbfs.

--
Mike Kravetz

> you need to make sure there are no page references
> left around. For instance, on shmem any process might trigger the
> kernel to GUP mapped shmem pages for asynchronous IO, then unmap the
> file and request F_SEAL_WRITE. In this case the seal must be rejected
> *iff* the pages are still pinned. shmem does this by requiring the
> page-refcounts to be 0. Preferably there would be some better
> infrastructure that tells us whether someone operates on those pages,
> but this does not exist right now. See shmem_wait_for_pins() for
> details.
>
> I have little knowledge on how hugetlbs integrate with the page-cache
> and radix-tree, hence I'd prefer if someone can explicitly ACK that
> shmem_wait_for_pins() is suitable for hugetlbfs.
>
> Otherwise, this series looks good to me (minus the #ifdef mess..).
>
> Thanks
> David
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=ilto:"dont@kvack.org"> email@kvack.org </a>
>

\
 
 \ /
  Last update: 2017-11-03 18:14    [W:0.077 / U:5.200 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site