Re: [PATCH] KVM: VMX: Fix 32bit Windows blue screen with EPT

[Sheng Yang <sheng@linux.intel.com>]

On Thursday 30 December 2010 17:14:23 Avi Kivity wrote:
> On 12/30/2010 11:05 AM, Sheng Yang wrote:
> > >  >    	if (!(cr0&   X86_CR0_PG)) {
> > >  >    	
> > >  >    		/* From paging/starting to nonpaging */
> > >  >    		vmcs_write32(CPU_BASED_VM_EXEC_CONTROL,
> > >  >  
> > >  >  @@ -1937,11 +1936,8 @@ static void
> > >  >  ept_update_paging_mode_cr0(unsigned long *hw_cr0,
> > >  >  
> > >  >    			vmcs_read32(CPU_BASED_VM_EXEC_CONTROL)&
> > >  >    			
> > >  >    			~(CPU_BASED_CR3_LOAD_EXITING |
> > >  >    			
> > >  >    			CPU_BASED_CR3_STORE_EXITING));
> > >  >  
> > >  >  -		/* Must fetch cr3 before updating cr0 */
> > >  >  -		cr3 = kvm_read_cr3(vcpu);
> > >  >  
> > >  >    		vcpu->arch.cr0 = cr0;
> > >  >    		vmx_set_cr4(vcpu, kvm_read_cr4(vcpu));
> > >  >  
> > >  >  -		vmx_set_cr3(vcpu, cr3);
> > >  
> > >  This is indeed bogus.  But what ensures that we'll have the correct
> > >  GUEST_CR3 after enabling paging?
> > 
> > In fact I don't understand why we need this line. All modification is for
> > CR3 reading, why we need to set hardware CR3 again? It should be the
> > same as when we don't have CR3 accessor I think.
> 
> when cr0.pg=0 then we set GUEST_CR3=identity_pagetable.  We don't want
> that when we we switch to paging mode.

I think kvm_mmu_reset_context() in kvm_set_cr0() should cover this?

--
regards
Yang, Sheng