Re: [PATCH 13/15] KVM: nVMX: Update vmcs02 GUEST_IA32_DEBUGCTL only when vmcs12 is dirty

Paolo Bonzini
2019-06-06T16:39:40Z

On 07/05/19 18:06, Sean Christopherson wrote:
> VMWRITEs to GUEST_IA32_DEBUGCTL from L1 are always intercepted, and
> unlike GUEST_DR7 there is no funky logic for determining the value.
>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/vmx/nested.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 2e9f8169d40a..58717dfe82c9 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2194,6 +2194,11 @@ static void prepare_vmcs02_full(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
> vmcs_write64(GUEST_PDPTR2, vmcs12->guest_pdptr2);
> vmcs_write64(GUEST_PDPTR3, vmcs12->guest_pdptr3);
> }
> +
> + if (vmx->nested.nested_run_pending &&
> + (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS))
> + vmcs_write64(GUEST_IA32_DEBUGCTL,
> + vmcs12->guest_ia32_debugctl);
> }
>
> if (nested_cpu_has_xsaves(vmcs12))
> @@ -2270,7 +2275,6 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
> if (vmx->nested.nested_run_pending &&
> (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) {
> kvm_set_dr(vcpu, 7, vmcs12->guest_dr7);
> - vmcs_write64(GUEST_IA32_DEBUGCTL, vmcs12->guest_ia32_debugctl);
> } else {
> kvm_set_dr(vcpu, 7, vcpu->arch.dr7);
> vmcs_write64(GUEST_IA32_DEBUGCTL, vmx->nested.vmcs01_debugctl);
>

I'm passing on this one. It really gets more complicated and I'm not
sure the savings are worth it.

Paolo