Re: [PATCH] KVM: vmx: Fix the broken usage of vmx_xsaves_supported

[Xiaoyao Li]

On 6/20/2019 4:17 PM, Paolo Bonzini wrote:
> On 20/06/19 08:46, Xiaoyao Li wrote:
> > > It depends on whether or not processors support the 1-setting instead
> > > of âenable XSAVES/XRSTORSâ is 1 in VM-exection control field. Anyway,
> >
> > Yes, whether this field exist or not depends on whether processors
> > support the 1-setting.
> >
> > But if "enable XSAVES/XRSTORS" is clear to 0, XSS_EXIT_BITMAP doesn't
> > work. I think in this case, there is no need to set this vmcs field?
>
> vmx->secondary_exec_control can change; you are making the code more
> complex by relying on the value of the field at the point of vmx_vcpu_setup.
At this point. Agreed. It's harmless to set a default value.

> I do _think_ your version is incorrect, because at this point CPUID has
> not been initialized yet and therefore
> vmx_compute_secondary_exec_control has not set SECONDARY_EXEC_XSAVES.

SECONDARY_EXEC_XSAVES is in the opt when setup_vmcs_config, and 
vmx_compute_secondary_exec_control() is to clear SECONDARY_EXEC_XSAVES 
based on guest cpuid.

> However I may be wrong because I didn't review the code very closely:
> the old code is obvious and so there is no point in changing it.

you mean this part about XSS_EXIT_BITMAP? how about the other part in 
vmx_set/get_msr() in this patch?

> Paolo