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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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?

Jan


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