Re: [PATCH 2/2] X86: allow access to EFER in 32bit KVM

["Joerg Roedel" <joerg.roedel-5C7GfCeVMHo@public.gmane.org>]

On Wed, Jan 30, 2008 at 03:11:36PM +0200, Avi Kivity wrote:
> Joerg Roedel wrote:
> >This patch makes the EFER register accessible on a 32bit KVM host. This is
> >necessary to boot 32 bit PAE guests under SVM.
> >
> >  
> 
> 
> > static void set_efer(struct kvm_vcpu *vcpu, u64 efer)
> > {
> > 	if (efer & EFER_RESERVED_BITS) {
> >@@ -432,12 +430,19 @@ static void set_efer(struct kvm_vcpu *vcpu, u64 efer)
> > 		return;
> > 	}
> > +#ifdef CONFIG_X86_64
> > 	if (is_paging(vcpu)
> > 	    && (vcpu->arch.shadow_efer & EFER_LME) != (efer & EFER_LME)) {
> > 		printk(KERN_DEBUG "set_efer: #GP, change LME while paging\n");
> > 		kvm_inject_gp(vcpu, 0);
> > 		return;
> > 	}
> >+#else
> >+	if (efer & EFER_LME) {
> >+		printk(KERN_DEBUG "set_efer: #GP, enable longmode on 32bit host\n");
> >+		kvm_inject_gp(vcpu, 0);
> >+	}
> >+#endif
> >  
> 
> We should, in addition, check the various EFER bits against host cpu capabilities (with cpu_has()). This 
> will ensure that any attempt to set an invalid bit will fail.  On Intel cpus that don't have EFER, there are 
> no valid bits, and if we detect that in vmx_set_efer, we can make it work on hosts that don't have EFER.

Ok, makes sense. I will update the patches.

Joerg

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