Re: [RFC PATCH 03/21] i386/kvm: handle Xen HVM cpuid leaves

From: David Woodhouse <dwmw2@infradead.org>
To: "Philippe Mathieu-Daudé" <philmd@linaro.org>, qemu-devel@nongnu.org
Cc: Paolo Bonzini <pbonzini@redhat.com>, Paul Durrant <paul@xen.org>,
	Joao Martins <joao.m.martins@oracle.com>,
	Ankur Arora <ankur.a.arora@oracle.com>
Subject: Re: [RFC PATCH 03/21] i386/kvm: handle Xen HVM cpuid leaves
Date: Tue, 06 Dec 2022 00:18:32 +0000	[thread overview]
Message-ID: <ba4fcebc4f3032d4cbf09928a8a0c37389dd6e72.camel@infradead.org> (raw)
In-Reply-To: <68be4619-50a1-83a9-290d-05618002b47d@linaro.org>

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On Mon, 2022-12-05 at 22:58 +0100, Philippe Mathieu-Daudé wrote:
> > 
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 22b681ca37..45aa9e40a5 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -7069,6 +7069,8 @@ static Property x86_cpu_properties[] = {
> >        * own cache information (see x86_cpu_load_def()).
> >        */
> >       DEFINE_PROP_BOOL("legacy-cache", X86CPU, legacy_cache, true),
> > +    DEFINE_PROP_BOOL("xen", X86CPU, xen, false),
> 
> Maybe name it 'xen-hvm'?

I think I'd prefer it to go away completely. If the *machine* has the
Xen feature enabled (which I've made implicit in the 'xen-version'
property), perhaps we should *always* disable 'expose_kvm' and enable
the Xen CPUID leaves instead? 

> > +    DEFINE_PROP_BOOL("xen-vapic", X86CPU, xen_vapic, false),
> 
> What happens if we use -cpu host,-kvm,+xen,-xen-vapic ?

That's sane; it does the Xen CPUID thing but doesn't advertise the
vAPIC feature in the Xen CPUID leaves.

> Is -cpu host,-kvm,-xen,+xen-vapic meaningful? Otherwise we need to error
> out (eventually displaying some hint).

Indeed it isn't meaningful, and should cause an error.

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