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    SubjectRe: [PATCH v3 7/8] KVM:X86: Add XSS bit 11 and 12 support for CET xsaves/xrstors.
    On Mon, Mar 11, 2019 at 04:32:32PM +0100, Paolo Bonzini wrote:
    > On 10/03/19 14:35, Yang Weijiang wrote:
    > >>>> - if (data != 0)
    > >>>> + if (data & ~kvm_supported_xss())
    > >>>> return 1;
    > >>> You should instead check this against CPUID[0xD, 1].EDX:ECX. If CET is
    > >>> disabled in CPUID, the guest should not be able to set it in MSR_IA32_CSS.
    > >>>
    > >>> Paolo
    > >> Thanks, OK, will change it.
    > > Hi, Paolo,
    > > How about change kvm_supported_xss() as below so that CPUID[0xd,1] check
    > > is implied in host_xss contents, vmx_supported_xss() now just returns host_xss
    > > in vmx.c. The purpose of this change is to make XSS data check
    > > common for other XSS based features.
    > >
    > > +u64 kvm_supported_xss(void)
    > > +{
    > > + return KVM_SUPPORTED_XSS & kvm_x86_ops->vmx_supported_xss();
    > > +}
    > > +
    > >
    >
    > This is correct; however, you should also check against the *guest*'s
    > CPUID[0xD, 1].EDX:ECX.
    >
    > One possibility is to add a field kvm->guest_supported_xss and update it
    > in kvm_update_cpuid, then here you do
    >
    > if (data & ~kvm->guest_supported_xss)
    > return 1;
    >
    > Thanks,
    >
    > Paolo
    Thanks Paolo, I'll add the change in next version.

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