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

[Andrew Morton]

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?