Re: [Xen-devel] [PATCH] x86/hvm: avoid p2m lookups for vlapic accesses.

[Tim Deegan <tim@xxxxxxx>]

At 09:49 +0100 on 10 May (1368179395), Jan Beulich wrote:
> >>> On 09.05.13 at 14:12, Tim Deegan <tim@xxxxxxx> wrote:
> > commit ae8868ff4fc5a56e729399b031b27157d94febbf
> > Author: Tim Deegan <tim@xxxxxxx>
> > Date:   Thu May 9 13:06:53 2013 +0100
> > 
> >     x86/hvm: avoid p2m lookups for vlapic accesses.
> >     
> >     The LAPIC base address is a known GFN, so we can skip looking up the
> >     p2m: we know it should be handled as emulated MMIO.  That helps
> >     performance in older Windows OSes, which make a _lot_ of TPR accesses.
> >     
> >     This will change the behaviour of any OS that maps other
> >     memory/devices at its LAPIC address; the new behaviour (the LAPIC
> >     mapping always wins) is closer to actual hardware behaviour.
> >     
> >     Signed-off-by: Tim Deegan <tim@xxxxxxx>
> 
> I'd prefer PFN_DOWN() to be used instead of the explicit shifts,

Good point; done.

> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> along with the question whether this should be backported later to
> 4.2/4.1.

I think it should be considered for 4.2; no need for it in 4.1 as the
p2m changes that caused the problem only appear in 4.2

Cheers,

Tim

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