Re: [Xen-devel] [V10 PATCH 23/23] PVH xen: introduce vmexit handler for PVH

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.08.13 at 00:51, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> On Fri, 23 Aug 2013 08:16:40 +0100
> "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>> >>> On 23.08.13 at 01:22, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
>> >>> wrote:
>> > In general, we should have less interecepts for PVH, eg, there
>> > should be no MSR_IA32_CR_PAT intercept.
>> 
>> How that? All memory management supposedly is HVM-like, and
>> PAT is an integral part of memory management. Unless I'm
>> mistaken, not intercepting PAT writes would mean you allow the
>> guest access to the physical MSR, which surely is wrong.
> 
> Here's HVM code:
> 
>     if ( cpu_has_vmx_pat && paging_mode_hap(d) )
>         vmx_disable_intercept_for_msr(v, MSR_IA32_CR_PAT,
>             MSR_TYPE_R | MSR_TYPE_W);
> 
> We require both for PVH, see pvh_check_requirements. My understanding,
> guest would write to GUEST_PAT and not HOST_PAT.

Ah, right, sorry - I forgot that VMX already has built in separation
of them.

Jan


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