Re: [PATCH v3] KVM: x86: Sync the states size with the XCR0/IA32_XSS at, any time

[Paolo Bonzini]

On 1/26/22 17:37, Sean Christopherson wrote:
> On Sun, Jan 23, 2022, Like Xu wrote:
> > From: Like Xu <likexu@xxxxxxxxxxx>
> >
> > XCR0 is reset to 1 by RESET but not INIT and IA32_XSS is zeroed by
> > both RESET and INIT. The kvm_set_msr_common()'s handling of MSR_IA32_XSS
> > also needs to update kvm_update_cpuid_runtime(). In the above cases, the
> > size in bytes of the XSAVE area containing all states enabled by XCR0 or
> > (XCRO | IA32_XSS) needs to be updated.
> >
> > For simplicity and consistency, existing helpers are used to write values
> > and call kvm_update_cpuid_runtime(), and it's not exactly a fast path.
> >
> > Fixes: a554d207dc46 ("KVM: X86: Processor States following Reset or INIT")
> > Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
> > ---
> > v2 -> v3 Changelog:
> > - Apply s/legacy/existing in the commit message; (Sean)
> > - Invoke kvm_update_cpuid_runtime() for MSR_IA32_XSS; (Sean)
> >
> >   arch/x86/kvm/x86.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 55518b7d3b96..4b509b26d9ab 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -3535,6 +3535,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct
> > msr_data *msr_info)
> >   		if (data & ~supported_xss)
> >   			return 1;
> >   		vcpu->arch.ia32_xss = data;
> > +		kvm_update_cpuid_runtime(vcpu);
> >   		break;
> >   	case MSR_SMI_COUNT:
> >   		if (!msr_info->host_initiated)
> > @@ -11256,7 +11257,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> >
> >   		vcpu->arch.msr_misc_features_enables = 0;
> >
> > -		vcpu->arch.xcr0 = XFEATURE_MASK_FP;
> > +		__kvm_set_xcr(vcpu, 0, XFEATURE_MASK_FP);
> >   	}
> >
> >   	/* All GPRs except RDX (handled below) are zeroed on RESET/INIT. */
> > @@ -11273,7 +11274,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> >   	cpuid_0x1 = kvm_find_cpuid_entry(vcpu, 1, 0);
> >   	kvm_rdx_write(vcpu, cpuid_0x1 ? cpuid_0x1->eax : 0x600);
> >
> > -	vcpu->arch.ia32_xss = 0;
> > +	__kvm_set_msr(vcpu, MSR_IA32_XSS, 0, true);
>
> Heh, this now conflicts with a patch Xiaoyao just posted, turns out the SDM was
> wrong.  I think there's also some whitespace change or something that prevents
> this from applying cleanly.  For convenience, I'll post a miniseries with this
> and Xiaoyao's patch.
>
> [*] https://lore.kernel.org/all/20220126034750.2495371-1-xiaoyao.li@xxxxxxxxx

It's okay, fixing the conflict in Xiaoyao's patch is trivial 
and---anyway---KVM does not support XSS != 0 for now so his patch 
doesn't really have any practical effect.

Like's patch queued, thanks.

Paolo