Re: [PATCH 08/10] x86/cpuid: Handle leaf 0xb in guest_cpuid()

From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH 08/10] x86/cpuid: Handle leaf 0xb in guest_cpuid()
Date: Wed, 22 Feb 2017 02:16:37 -0700	[thread overview]
Message-ID: <58AD6505020000780013CA32@prv-mh.provo.novell.com> (raw)
In-Reply-To: <1487588434-4359-9-git-send-email-andrew.cooper3@citrix.com>

>>> On 20.02.17 at 12:00, <andrew.cooper3@citrix.com> wrote:
> Leaf 0xb is reserved by AMD, and uniformly hidden from guests by the toolstack
> logic and hypervisor PV logic.
> 
> The previous dynamic logic filled in the x2APIC ID for all HVM guests.  This
> is modified to respect the entire leaf being reserved by AMD, but is altered
> to include PV Intel guests, so they get more sensible values in their emulated
> and faulted view of CPUID.

Don't we expose x2APIC to HVM guests even on AMD systems? In
which case we surely will want to also expose the x2APIC ID.

> @@ -959,6 +950,14 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf,
>          }
>          break;
>  
> +    case 0xb:
> +        if ( p->x86_vendor == X86_VENDOR_INTEL )
> +        {
> +            /* Fix the x2APIC identifier. */
> +            res->d = v->vcpu_id * 2;
> +        }
> +        break;

Irrespective of the comment above, wouldn't the if() here better
look at the x2APIC feature flag of the domain?

Jan

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