RE: [Xen-devel] Re: One potential issue of shadow fault emulation

["Cui, Dexuan" <dexuan.cui@xxxxxxxxx>]

I believe this emulation issue accounts for several weird vTPR-related
bugs.

-- Dexuan

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
Sent: Saturday, December 22, 2007 5:54 AM
To: Tim Deegan; Jiang, Yunhong
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Re: One potential issue of shadow fault emulation

On 21/12/07 17:21, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:

> I think it's cleanest to just fail the emulation if we find we're
> writing to the vlapic, rather than adding special-case code to detect
> and handle TPR writes within the page.  Unless this is a particularly
> common path and would have a measurable performance impact for the
extra
> VMEXIT.

Probably gfn_to_mfn() should explicitly check for vmx_apic_access_mfn
and
return INVALID_MFN instead. That will fix all emulation routines by
causing
them to take their mmio path (or bail if they don't have them) which is
the
correct behaviour for this case.

This is certainly important enough to fix for 3.2.0 (and 3.1.3).

 -- Keir


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