Re: [Xen-devel] [PATCH] x86/mm: Take the p2m lock even in shadow mode.

[Tim Deegan <tim@xxxxxxx>]

At 14:29 +0000 on 21 Feb (1361456940), Jan Beulich wrote:
> >>> On 21.02.13 at 15:21, Tim Deegan <tim@xxxxxxx> wrote:
> > The reworking of p2m lookups to use get_gfn()/put_gfn() left the
> > shadow code not taking the p2m lock, even in cases where the p2m would
> > be updated (i.e. PoD).
> > 
> > In many cases, shadow code doesn't need the exclusion that
> > get_gfn()/put_gfn() provides, as it has its own interlocks against p2m
> > updates, but this is taking things too far, and can lead to crashes in
> > the PoD code.
> > 
> > Now that most shadow-code p2m lookups are done with explicitly
> > unlocked accessors, or with the get_page_from_gfn() accessor, which is
> > often lock-free, we can just turn this locking on.
> > 
> > The remaining locked lookups are in sh_page_fault() (in a path that's
> > almost always already serializing on the paging lock), and in
> > emulate_map_dest() (which can probably be updated to use
> > get_page_from_gfn()).  They're not addressed here but may be in a
> > follow-up patch.
> 
> I assume once coming out of stage testing, this also needs to be
> put into 4.2?

Yes, sorry I forgot to mention it.  Definitely a candidate for 4.2

Tim.

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