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

From: Andrew Morton <akpm@linux-foundation.org>
To: Suzuki K Poulose <Suzuki.Poulose@arm.com>
Cc: Jia He <hejianet@gmail.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Minchan Kim <minchan@kernel.org>,
	Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>,
	Arvind Yadav <arvind.yadav.cs@gmail.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	jia.he@hxt-semitech.com, Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm
Date: Thu, 24 May 2018 13:38:05 -0700	[thread overview]
Message-ID: <20180524133805.6e9bfd4bf48de065ce1d7611@linux-foundation.org> (raw)
In-Reply-To: <6c417ab1-a808-72ea-9618-3d76ec203684@arm.com>

On Thu, 24 May 2018 09:44:16 +0100 Suzuki K Poulose <Suzuki.Poulose@arm.com> 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@gmail.com> 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@hxt-semitech.com
> >>
> >> I assumed you wanted this patch to be committed as
> >> From:jia.he@hxt-semitech.com rather than From:hejianet@gmail.com, 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 ?
> 

I have it scheduled for 4.18-rc1, with a cc:stable for backporting.

I'd normally put such a fix into 4.17-rcX but I'd like to give Hugh
time to review it and to generally give it a bit more time for review
and test.

Have you tested it yourself?