Re: [Qemu-devel] [PATCH 4/4] x86: Support feature=force on the command-line

[Eduardo Habkost]

On Thu, May 04, 2017 at 12:16:38PM +0200, Kashyap Chamarthy wrote:
> On Tue, May 02, 2017 at 05:31:15PM -0300, Eduardo Habkost wrote:
> 
> Hi,
> 
> Yet to try this series, a small question in-line.
> 
> > Introduce a new CPUFeatureSetting QAPI data type, and use it to support
> > feature=force on -cpu.
> > 
> > Signed-off-by: Eduardo Habkost <address@hidden>
[...]
> > @@ -336,5 +340,13 @@ int main(int argc, char **argv)
> >                       "-machine accel=kvm:tcg -cpu max,mmx=off",
> >                       1, 0, "EDX", 23, false);
> >  
> > +    {
> > +    FeatureTestArgs *a;
> > +    a = add_feature_test("x86/cpuid/features/monitor-force",
> > +                         "-machine accel=kvm:tcg -cpu 486,monitor=force",
> 
> Following your above test example, should the 'force' boolean also work
> (understood: only for testing / debugging) as below, for a recognized
> CPUID flag, taking the example of 'INVPCID'?
> 
>   $ qemu-system-x86_64 [...] -cpu Haswell-noTSX,invpcid=force [...]

This would be valid syntax and would enable invpcid on CPUID,
yes. But on most cases this means you will get a broken VCPU
because the host won't virtualize the feature properly (if it
did, the feature would be reported as available in
GET_SUPPORTED_CPUID and "feature=on" would already work).

-- 
Eduardo