Re: [PATCH v6 7/7] KVM: SVM: Add Page modification logging support

[Yosry Ahmed <yosry@kernel.org>]

On Wed, Apr 22, 2026 at 11:56:43AM +0530, Nikunj A. Dadhania wrote:
> 
> 
> On 4/22/2026 4:45 AM, Sean Christopherson wrote:
> > On Tue, Apr 21, 2026, Yosry Ahmed wrote:
> >>> @@ -3253,6 +3278,54 @@ static int bus_lock_exit(struct kvm_vcpu *vcpu)
> >>>  	return 0;
> >>>  }
> >>>  
> >>> +void svm_update_cpu_dirty_logging(struct kvm_vcpu *vcpu)
> >>> +{
> >>> +	struct vcpu_svm *svm = to_svm(vcpu);
> >>> +
> >>> +	if (WARN_ON_ONCE(!vcpu->kvm->arch.cpu_dirty_log_size))
> >>> +		return;
> >>> +
> >>> +	guard(svm_vmcb01)(vcpu);
> >>
> >> Why do we need this? Why not update vmcb01 directly below?
> 
> Are you suggesting something like below:

Yes.

> 
> void svm_update_cpu_dirty_logging(struct kvm_vcpu *vcpu)
> {
> 	struct vcpu_svm *svm = to_svm(vcpu);
> 	struct vmcb *vmcb01 = svm->vmcb01.ptr;
> 
> 	if (WARN_ON_ONCE(!vcpu->kvm->arch.cpu_dirty_log_size))
> 		return;
> 
> 	/*
> 	 * Note, nr_memslots_dirty_logging can be changed concurrent with this
> 	 * code, but in that case another update request will be made and so
> 	 * the guest will never run with a stale PML value.
> 	 */
> 	if (atomic_read(&vcpu->kvm->nr_memslots_dirty_logging))
> 		vmcb01->control.nested_ctl |= SVM_NESTED_CTL_PML_ENABLE;
> 	else
> 		vmcb01->control.nested_ctl &= ~SVM_NESTED_CTL_PML_ENABLE;
> 
> 	vmcb_mark_dirty(vmcb01, VMCB_NPT);
> }