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Date: Mon, 16 Apr 2018 13:33:03 -0300
From: Eduardo Habkost <ehabkost@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] WHPX fixes an issue with CPUID 1 not
 returning CPUID_EXT_HYPERVISOR
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Justin Terry (VM)" <juterry@microsoft.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "rth@twiddle.net" <rth@twiddle.net>

On Thu, Apr 05, 2018 at 05:50:20PM +0200, Paolo Bonzini wrote:
> On 28/03/2018 22:48, Justin Terry (VM) wrote:
[...]
> > If we use [2] to inject the answers at creation time WHPX needs access
> > to the CPUX86State at accel init which also doesn't seem to be possible
> > in QEMU today. WHPX could basically just call cpu_x86_cpuid() for each
> > CPUID QEMU cares about and plumb the answer before start. This has the
> > best performance as we avoid the additional exits but has an issue in
> > that the results must be known ahead of time.
> 
> The earliest where you have access to that is x86_cpu_initfn.

x86_cpu_initfn() is the earliest you have access to the CPU
object, but note that the final CPUID bits (based on -cpu
options, accel data, and possibly other input) are known only
when x86_cpu_realizefn() is called.

-- 
Eduardo