Re: [PATCH 3/3] KVM: SVM: Lazy fpu for npt

[Joerg Roedel <joro@8bytes.org>]

On Thu, Jan 07, 2010 at 02:15:44PM +0200, Avi Kivity wrote:
> If two conditions apply:
>  - no bits outside TS and EM differ between the host and guest cr0
>  - the fpu is active
> 
> then we can activate the selective cr0 write intercept and drop the
> unconditional cr0 read and write intercept, and allow the guest to run
> with the host fpu state.  This reduces the heavyweight context switch
> when npt is enabled.


> -	if (npt_enabled) {
> -		int mmu_reload = 0;
> -		if ((kvm_read_cr0_bits(vcpu, X86_CR0_PG) ^ svm->vmcb->save.cr0)
> -		    & X86_CR0_PG) {
> -			svm_set_cr0(vcpu, svm->vmcb->save.cr0);
> -			mmu_reload = 1;
> -		}
> +	if (!(svm->vmcb->control.intercept_cr_write & INTERCEPT_CR0_MASK))
>  		vcpu->arch.cr0 = svm->vmcb->save.cr0;
> +	if (npt_enabled)
>  		vcpu->arch.cr3 = svm->vmcb->save.cr3;
> -		if (mmu_reload) {
> -			kvm_mmu_reset_context(vcpu);
> -			kvm_mmu_load(vcpu);
> -		}
> -	}
> -

Hmm, I think removing this hack is a seperate issue. Should it be a
sepearte patch which enables cr0 intercept for npt and removes these
lines? It makes this change more clear in the logs.

Joerg