Re: [Xen-devel] [PATCH 6/6] AMD-PVH: enable pvh if requirements met

[Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>]

On Wed, Jun 24, 2015 at 07:24:18PM +0100, Andrew Cooper wrote:
> On 24/06/15 08:49, Jan Beulich wrote:
> >>>> On 24.06.15 at 04:34, <boris.ostrovsky@xxxxxxxxxx> wrote:
> >> On 06/23/2015 08:30 AM, Jan Beulich wrote:
> >>>>>> On 22.06.15 at 18:37, <elena.ufimtseva@xxxxxxxxxx> wrote:
> >>>> --- a/xen/arch/x86/hvm/svm/svm.c
> >>>> +++ b/xen/arch/x86/hvm/svm/svm.c
> >>>> @@ -1444,6 +1444,9 @@ const struct hvm_function_table * __init
> >>>> start_svm(void)
> >>>>       svm_function_table.hap_capabilities = HVM_HAP_SUPERPAGE_2MB |
> >>>>           ((cpuid_edx(0x80000001) & 0x04000000) ? HVM_HAP_SUPERPAGE_1GB 
> >>>> : 0);
> >>>>   
> >>>> +    if ( cpu_has_svm_npt  && cpu_has_svm_decode )
> >>>> +        svm_function_table.pvh_supported = 1;
> >>> If svm_decode indeed is a prereq, then the earlier patch dealing
> >>> with the handle_mmio() invocations doesn't need to fiddle with
> >>> VMEXIT_INVLPG other than to maybe add a documenting ASSERT().
> >>>
> >> I am not sure we should require decode feature to be required for PVH 
> >> support. I can't remember exactly but I think this feature was first 
> >> introduced in family 15h so requiring it will leave at least family 10h 
> >> processors as not supporting PVH.
> > The question was why the dependency was added in the first place.
> > Indeed only fam 12, 15, and 16 have the field documented. Otoh
> > PVH isn't being supported universally on all VMX variants either...
> 
> Right, but this is a bug (feature?) of the current implementation and
> need fixing.
> 
> There are no technical reasons to prevent PVH guests running in any case
> where an HVM guest currently runs.
> 
> The only technical restriction I can think of is that a PVH hardware
> domain needs IOMMU support, but that is it.
> 

CCing Mukesh, maybe he will reply to as why that restriction is here.

> ~Andrew

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