Re: [Qemu-devel] [PATCH v5 2/3] x86: Data structure changes to support MSR based features

From: Eduardo Habkost <ehabkost@redhat.com>
To: Robert Hoo <robert.hu@linux.intel.com>
Cc: robert.hu@intel.com, pbonzini@redhat.com, rth@twiddle.net,
	thomas.lendacky@amd.com, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v5 2/3] x86: Data structure changes to support MSR based features
Date: Thu, 25 Oct 2018 10:36:37 -0300	[thread overview]
Message-ID: <20181025133637.GH4096@habkost.net> (raw)
In-Reply-To: <1540436819.80634.2.camel@linux.intel.com>

On Thu, Oct 25, 2018 at 11:06:59AM +0800, Robert Hoo wrote:
> On Wed, 2018-10-24 at 07:16 -0300, Eduardo Habkost wrote:
[...]
> > > +            struct {   /*CPUID that enumerate this MSR*/
> > > +                FeatureWord cpuid_class;
> > > +                uint32_t    cpuid_flag;
> > > +            } cpuid_dep;
> > 
> > Aren't you going to use this field anywhere?  Probably we want to
> > prevent the VM from starting if a bit is set in the feature world
> > but the cpuid_dep bit is not set.
> > 
> > e.g.:
> >   qemu-system-x86_64 -cpu Skylake-Client,-arch-capabilities,+rsba
> > probably should fail to start.
> 
> How about in x86_cpu_filter_features() filters the MSR feature word, if
>  its dependent CPUID feature bit is not set?
> The filter results will be record in cpu->filtered_features, and print
> out, like other filtered features.

Sounds good to me.

-- 
Eduardo