Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm

[Suzuki K Poulose]

On 24/05/18 09:50, Jia He wrote:
> Hi Suzuki
>
> On 5/24/2018 4:44 PM, Suzuki K Poulose Wrote:
> > On 14/05/18 10:45, Suzuki K Poulose wrote:
> > > On 10/05/18 00:31, Andrew Morton wrote:
> > > > On Fri, 4 May 2018 11:11:46 +0800 Jia He <hejianet@xxxxxxxxx> wrote:
> > > >
> > > > > In our armv8a server(QDF2400), I noticed lots of WARN_ON caused by PAGE_SIZE
> > > > > unaligned for rmap_item->address under memory pressure tests(start 20 guests
> > > > > and run memhog in the host).
> > > > >
> > > > > ...
> > > > >
> > > > > In rmap_walk_ksm, the rmap_item->address might still have the STABLE_FLAG,
> > > > > then the start and end in handle_hva_to_gpa might not be PAGE_SIZE aligned.
> > > > > Thus it will cause exceptions in handle_hva_to_gpa on arm64.
> > > > >
> > > > > This patch fixes it by ignoring(not removing) the low bits of address when
> > > > > doing rmap_walk_ksm.
> > > > >
> > > > > Signed-off-by: jia.he@xxxxxxxxxxxxxxxx
> > > >
> > > > I assumed you wanted this patch to be committed as
> > > > From:jia.he@xxxxxxxxxxxxxxxx rather than From:hejianet@xxxxxxxxx, so I
> > > > made that change. Please let me know if this was inappropriate.
> > > >
> > > > You can do this yourself by adding an explicit From: line to the very
> > > > start of the patch's email text.
> > > >
> > > > Also, a storm of WARN_ONs is pretty poor behaviour. Is that the only
> > > > misbehaviour which this bug causes? Do you think the fix should be
> > > > backported into earlier kernels?
> >
> >
> > Jia, Andrew,
> >
> > What is the status of this patch ?
> >
> > Suzuki
> I thought the patch is merged into mmotm tree.
> http://www.ozlabs.org/~akpm/mmotm/series
> But I don't know what is the next step.

Hi Jia,

Thanks for the update. I think that should eventually hit mainline. When it does,
please could you send the patch to stable kernel versions too ?

Usually having a "Cc: stable@xxxxxxxxxxxxxxx" in the original patch (for
critical fixes) would have done the trick. But since we don't have it,
please send it following the stable kernel rules.

Cheers
Suzuki