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

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Message-ID: <20190310133528.GA24796@local-michael-cet-test.sh.intel.com>
Date:   Sun, 10 Mar 2019 21:35:29 +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>
Subject: Re: [PATCH v3 7/8] KVM:X86: Add XSS bit 11 and 12 support for CET
 xsaves/xrstors.

On Sun, Mar 10, 2019 at 08:20:30PM +0800, Yang Weijiang wrote:
> On Fri, Mar 08, 2019 at 12:32:04PM +0100, Paolo Bonzini wrote:
> > On 28/02/19 09:44, Yang Weijiang wrote:
> > >>>  		if (!vmx_xsaves_supported())
> > >>>  			return 1;
> > >>> +
> > >>>  		/*
> > >>> -		 * The only supported bit as of Skylake is bit 8, but
> > >>> -		 * it is not supported on KVM.
> > >>> +		 * Check bits being set are supported in KVM.
> > >> I'd drop the comment altogether, it's pretty obvious from the code that
> > >> were checking which bits are supported.
> > > you won't see these redundancies in next version ;)
> > >>>  		 */
> > >>> -		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();
+}
+