Date:   Tue, 21 Feb 2023 15:48:07 -0800
In-Reply-To: <20230221153306.qubx7tfmasnvodeu@linux.intel.com>
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References: <20230217231022.816138-1-seanjc@google.com> <20230217231022.816138-9-seanjc@google.com>
 <20230221152349.ulcjtbnvziair7ff@linux.intel.com> <20230221153306.qubx7tfmasnvodeu@linux.intel.com>
Message-ID: <Y/VYN3n/lHePiDxM@google.com>
Subject: Re: [PATCH 08/12] KVM: nSVM: Use KVM-governed feature framework to
 track "vVM{SAVE,LOAD} enabled"
From:   Sean Christopherson <seanjc@google.com>
To:     Yu Zhang <yu.c.zhang@linux.intel.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Tue, Feb 21, 2023, Yu Zhang wrote:
> > Sorry, why guest_cpuid_is_intel(vcpu)? Is it becasue that a AMD host with virtual
> > VMSAVE/VMLOAD capability will always expose this feature for all AMD guests? 
> 
> Oh, sorry. I missed the guest_cpuid_has() in kvm_governed_feature_check_and_set().
> So please just ignore my 2nd question.
> 
> As to the check of guest_cpuid_is_intel(), is it necessary?

Yes?  The comment in init_vmcb_after_set_cpuid() says:

		/*
		 * We must intercept SYSENTER_EIP and SYSENTER_ESP
		 * accesses because the processor only stores 32 bits.
		 * For the same reason we cannot use virtual VMLOAD/VMSAVE.
		 */

but I'm struggling to connect the dots to SYSENTER.  I suspect the comment is
misleading and has nothing to do 32-bit vs. 64-bit (or I'm reading it wrong) and
should be something like:

	/*
	 * Disable virtual VMLOAD/VMSAVE and intercept VMLOAD/VMSAVE if the
	 * guest CPU is Intel in order to inject #UD.
	 */

In other words, a non-SVM guest shouldn't be allowed to execute VMLOAD/VMSAVE.