Re: [Qemu-devel] [PATCH] i386: extended the cpuid level when Intel PT is enabled

[Kang, Luwei]

> > Intel Processor Trace required CPUID[0x14] but the cpuid level is 0xd
> > when create a kvm guest with e.g. "-cpu qemu64,+intel-pt".
> >
> > Signed-off-by: Luwei Kang <address@hidden>
> > ---
> >  target/i386/cpu.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c index
> > 2f54125..da477b3 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -5023,6 +5023,13 @@ static void x86_cpu_expand_features(X86CPU *cpu, 
> > Error **errp)
> >          x86_cpu_adjust_feat_level(cpu, FEAT_C000_0001_EDX);
> >          x86_cpu_adjust_feat_level(cpu, FEAT_SVM);
> >          x86_cpu_adjust_feat_level(cpu, FEAT_XSAVE);
> > +
> > +        /* Intel Processor Trace requires CPUID[0x14] */
> > +        if ((env->features[FEAT_7_0_EBX] & CPUID_7_0_EBX_INTEL_PT) &&
> > +             kvm_enabled()) {
> > +            x86_cpu_adjust_level(cpu, &cpu->env.cpuid_min_level, 0x14);
> > +        }
> 
> This will require a new machine-type compatibility flag to enable the new 
> behavior, so we don't change CPUID data under the guest feet during live 
> migration.

Hi Eduardo,
    Thanks for your reply. I have some question on your comments.
    The cpuid level come from specific machine-type (e.g. qemu64, 
Skylake-Server) and they are all 0xd, but Intel PT required 0x14 so I extend 
the cpuid level.
    I don't fully understand what is the "require a new machine-type 
compatibility flag" mean, I need to add a new flag in each machine-type? 
    I try to do live migration with "-cpu qemu64,+intel-pt" and "-cpu host" are 
all passed test. We didn't change the cpuid data during live migration just 
initialize the cpuid data when create a new vcpu. Please correct me if anything 
wrong.

Thanks,
Luwei Kang

> 
> > +
> >          /* SVM requires CPUID[0x8000000A] */
> >          if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM) {
> >              x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel,
> > 0x8000000A);
> > --
> > 1.8.3.1
> >
> 
> --
> Eduardo