On Tue, Nov 29, 2022, Maxim Levitsky wrote:
> the V_IRQ and v_TPR bits don't exist when virtual interrupt
> masking is not enabled, therefore the KVM should not copy these
> bits regardless of V_IRQ intercept.
Hmm, the APM disagrees:
The APIC's TPR always controls the task priority for physical interrupts, and the
V_TPR always controls virtual interrupts.
While running a guest with V_INTR_MASKING cleared to 0:
• Writes to CR8 affect both the APIC's TPR and the V_TPR register.
...
The three VMCB fields V_IRQ, V_INTR_PRIO, and V_INTR_VECTOR indicate whether there
is a virtual interrupt pending, and, if so, what its vector number and priority are.
IIUC, V_INTR_MASKING_MASK is mostly about EFLAGS.IF, with a small side effect on
TPR. E.g. a VMM could pend a V_IRQ but clear V_INTR_MASKING and expect the guest
to take the V_IRQ. At least, that's my reading of things.
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> ---
> arch/x86/kvm/svm/nested.c | 23 ++++++++---------------
> 1 file changed, 8 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 37af0338da7c32..aad3145b2f62fe 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -412,24 +412,17 @@ void nested_copy_vmcb_save_to_cache(struct vcpu_svm *svm,
> */
> void nested_sync_control_from_vmcb02(struct vcpu_svm *svm)
> {
> - u32 mask;
> + u32 mask = 0;
> svm->nested.ctl.event_inj = svm->vmcb->control.event_inj;
> svm->nested.ctl.event_inj_err = svm->vmcb->control.event_inj_err;
>
> - /* Only a few fields of int_ctl are written by the processor. */
> - mask = V_IRQ_MASK | V_TPR_MASK;
> - if (!(svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK) &&
> - svm_is_intercept(svm, INTERCEPT_VINTR)) {
> - /*
> - * In order to request an interrupt window, L0 is usurping
> - * svm->vmcb->control.int_ctl and possibly setting V_IRQ
> - * even if it was clear in L1's VMCB. Restoring it would be
> - * wrong. However, in this case V_IRQ will remain true until
> - * interrupt_window_interception calls svm_clear_vintr and
> - * restores int_ctl. We can just leave it aside.
> - */
> - mask &= ~V_IRQ_MASK;
> - }
> + /*
> + * Only a few fields of int_ctl are written by the processor.
> + * Copy back only the bits that are passed through to the L2.
Just "L2", not "the L2".
> + */
> +
Unnecessary newline.
> + if (svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK)
> + mask = V_IRQ_MASK | V_TPR_MASK;
>
> if (nested_vgif_enabled(svm))
> mask |= V_GIF_MASK;
> --
> 2.26.3
>
