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

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

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.

thanks
Mukesh


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