From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: KVM: VMX: do not overwrite uptodate vcpu->arch.cr3 on
 KVM_SET_SREGS
Date: Thu, 9 Jun 2011 14:11:23 -0300
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References: <20110606172747.GA30900@amt.cnet>
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Cc: kvm <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
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On Tue, Jun 07, 2011 at 11:24:49AM +0300, Avi Kivity wrote:
> On 06/06/2011 08:27 PM, Marcelo Tosatti wrote:
> >Only decache guest CR3 value if vcpu->arch.cr3 is stale.
> >Fixes loadvm with live guest.
> >
> >
> >@@ -2049,7 +2049,9 @@ static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
> >  					unsigned long cr0,
> >  					struct kvm_vcpu *vcpu)
> >  {
> >-	vmx_decache_cr3(vcpu);
> >+
> >+	if (!test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
> >+		vmx_decache_cr3(vcpu);
> >  	if (!(cr0&  X86_CR0_PG)) {
> >  		/* From paging/starting to nonpaging */
> >  		vmcs_write32(CPU_BASED_VM_EXEC_CONTROL,
> 
> Applied and queued, but I think there is something rotten here.  How
> does arch.cr3 get into GUEST_CR3 after KVM_SET_SREGS?  arch.cr3 is a
> supposed to be write-through cache - it only has a bit in
> regs_avail, not regs_dirty.


KVM_SET_SREGS sets good kvm->arch.cr3. Then vmx_decache_cr3 overwrites
kvm->arch.cr3 from GUEST_CR3, which is stale.