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Date: Fri, 3 Apr 2015 14:19:42 +0200
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
To: Bandan Das <bsd@redhat.com>
Cc: Joel Schopp <joel.schopp@amd.com>, Gleb Natapov <gleb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org,
        Joerg Roedel <joro@8bytes.org>, Borislav Petkov <bp@alien8.de>,
        linux-kernel@vger.kernel.org, David Kaplan <david.kaplan@amd.com>
Subject: Re: [PATCH] kvm: x86: svm: remove SVM_EXIT_READ_CR* intercepts
Message-ID: <20150403121941.GB28325@potion.brq.redhat.com>
References: <20150312201746.2953.11716.stgit@joelvm2.amd.com>
 <jpgk2yl9aqr.fsf@redhat.com>
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2015-03-12 17:17-0400, Bandan Das:
> Joel Schopp <joel.schopp@amd.com> writes:
> > @@ -2968,29 +2964,10 @@ static int cr_interception(struct vcpu_svm *svm)
> >  			kvm_queue_exception(&svm->vcpu, UD_VECTOR);
> >  			return 1;
> >  		}
> > -	} else { /* mov from cr */
> > -		[reads of CR 0..8]
> > +	} else { /* mov from cr, should never trap in svm */
> > +		WARN(1, "unhandled read from CR%d", cr);
> > +		kvm_queue_exception(&svm->vcpu, UD_VECTOR);
> > +		return 1;
> 
> Can we end up here if a nested hypervisor sets cr read interception ?

No.  If the nested hypervisor sets intercept bits, we're going to detect
them in 'handle_exit -> nested_svm_exit_handled -> nested_svm_intercept'
and enter L1 before the cr_interception handler.