Sure, uploaded https://lkml.org/lkml/2018/2/6/856. PTAL.

jin


On Tue, Feb 6, 2018 at 3:38 PM Eric Biggers <ebiggers3@gmail.com> wrote:

> On Tue, Feb 06, 2018 at 06:11:49PM -0500, Theodore Ts'o wrote:
> > On Tue, Feb 06, 2018 at 12:39:53PM -0800, Greg KH wrote:
> > > On Tue, Feb 06, 2018 at 11:09:37AM -0800, Jin Qian wrote:
> > > > From: Jin Qian <jinqian@google.com>
> > > >
> > > > partial backport from 21fc61c73c3903c4c312d0802da01ec2b323d174
> upstream
> > > > to v4.4 to prevent virt_to_page on highmem.
> > >
> > > Ted, any objection to this patch?
> >
> > No objections with my ext4 hat on.
> >
> > It should be noted though that this is a partial backport because it
> > only fixes ext4, while Al's original upstream fix addressed a much
> > larger set of file systems.  In the Android kernel the f2fs fix had
> > been backported separately.  But for the upstream kernel, it *might*
> > be the case that we should try backporting the original commit so that
> > in case there is some other general purpose distribution decides (a)
> > to base their system on 4.4, and (b) support a 32-bit kernel, they get
> > the more general bug fixes which applies for btrfs, isofs, ocfs2, nfs,
> > etc.
> >
> > I haevn't been paying attention to what LTS kernels general purpose
> > distro's are using, so I don't know how important this would be.  And
> > if there are companies like Cloudflare which are using upstream LTS
> > kernel, it seems unlikely they would want to use a 32-bit kernel,
> > so.... shrug.  Greg, I'll let you decide if you want to backport the
> > full commit or not.
> >
> > (We had a similar discussion on the AOSP kernel, and came to the
> > conclusion that we only needed to make the patch support ext4.  No one
> > was going to test the other file systems besides ext4 and f2fs,
> > anyway.  But the calculus might be different might be different for
> > the general upstream LTS kernel.)
> >
>
> Well, the main point of backporting this change is to fix symlink
> decryption on
> 32-bit systems.  So, it would be needed on both ext4 and f2fs.  Jin, it
> might be
> a good idea to fix f2fs in this patch at well, since unlike the AOSP
> kernels,
> the LTS kernels do not have the latest f2fs backported to them.
>
> I don't think backporting this change for other filesystems is particularly
> important, since if I understand correctly, the reasons that Al made the
> change
> originally were:
>
> - to allow following symlinks in RCU mode, but that's not implemented in
> old
>   kernels
>
> - to prevent a process from using up all kmaps and deadlocking the system,
> which
>   I'm not sure is a real problem (someone would need to try to put
> together a
>   reproducer), but if so it would probably just be a local device of
> service.
>
> Also if we actually backported the full commit there are follow-on fixes
> such as
> e8ecde25f5e that would be needed as well but might be missed.
>
> Thanks,
>
> - Eric
>