linux-kernel - Re: [PATCH v3 7/8] KVM:X86: Add XSS bit 11 and 12 support for CET xsaves/xrstors.

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Date:   Tue, 12 Mar 2019 22:30:10 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
        yu-cheng.yu@...el.com, Zhang Yi Z <yi.z.zhang@...ux.intel.com>,
        weijiang.yang@...el.com
Subject: Re: [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.