Re: [PATCH v3] KVM: x86: Disable posted interrupts for odd IRQs

[Wanpeng Li]

On Thu, 5 Sep 2019 at 21:46, Alexander Graf <graf@xxxxxxxxxx> wrote:
>
> We can easily route hardware interrupts directly into VM context when
> they target the "Fixed" or "LowPriority" delivery modes.
>
> However, on modes such as "SMI" or "Init", we need to go via KVM code
> to actually put the vCPU into a different mode of operation, so we can
> not post the interrupt
>
> Add code in the VMX and SVM PI logic to explicitly refuse to establish
> posted mappings for advanced IRQ deliver modes. This reflects the logic
> in __apic_accept_irq() which also only ever passes Fixed and LowPriority
> interrupts as posted interrupts into the guest.
>
> This fixes a bug I have with code which configures real hardware to
> inject virtual SMIs into my guest.
>
> Signed-off-by: Alexander Graf <graf@xxxxxxxxxx>

Reviewed-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>

>
> ---
>
> v1 -> v2:
>
>   - Make error message more unique
>   - Update commit message to point to __apic_accept_irq()
>
> v2 -> v3:
>
>   - Use if() rather than switch()
>   - Move abort logic into existing if() branch for broadcast irqs
>   -> remove the updated error message again (thus remove R-B tag from Liran)
>   - Fold VMX and SVM changes into single commit
>   - Combine postability check into helper function kvm_irq_is_postable()
> ---
>  arch/x86/include/asm/kvm_host.h | 7 +++++++
>  arch/x86/kvm/svm.c              | 4 +++-
>  arch/x86/kvm/vmx/vmx.c          | 6 +++++-
>  3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 44a5ce57a905..5b14aa1fbeeb 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1581,6 +1581,13 @@ bool kvm_intr_is_single_vcpu(struct kvm *kvm, struct kvm_lapic_irq *irq,
>  void kvm_set_msi_irq(struct kvm *kvm, struct kvm_kernel_irq_routing_entry *e,
>                      struct kvm_lapic_irq *irq);
>
> +static inline bool kvm_irq_is_postable(struct kvm_lapic_irq *irq)
> +{
> +       /* We can only post Fixed and LowPrio IRQs */
> +       return (irq->delivery_mode == dest_Fixed ||
> +               irq->delivery_mode == dest_LowestPrio);
> +}
> +
>  static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
>  {
>         if (kvm_x86_ops->vcpu_blocking)
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 1f220a85514f..f5b03d0c9bc6 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5260,7 +5260,8 @@ get_pi_vcpu_info(struct kvm *kvm, struct kvm_kernel_irq_routing_entry *e,
>
>         kvm_set_msi_irq(kvm, e, &irq);
>
> -       if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
> +       if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu) ||
> +           !kvm_irq_is_postable(&irq)) {
>                 pr_debug("SVM: %s: use legacy intr remap mode for irq %u\n",
>                          __func__, irq.vector);
>                 return -1;
> @@ -5314,6 +5315,7 @@ static int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
>                  * 1. When cannot target interrupt to a specific vcpu.
>                  * 2. Unsetting posted interrupt.
>                  * 3. APIC virtialization is disabled for the vcpu.
> +                * 4. IRQ has incompatible delivery mode (SMI, INIT, etc)
>                  */
>                 if (!get_pi_vcpu_info(kvm, e, &vcpu_info, &svm) && set &&
>                     kvm_vcpu_apicv_active(&svm->vcpu)) {
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 570a233e272b..63f3d88b36cc 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7382,10 +7382,14 @@ static int vmx_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
>                  * irqbalance to make the interrupts single-CPU.
>                  *
>                  * We will support full lowest-priority interrupt later.
> +                *
> +                * In addition, we can only inject generic interrupts using
> +                * the PI mechanism, refuse to route others through it.
>                  */
>
>                 kvm_set_msi_irq(kvm, e, &irq);
> -               if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
> +               if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu) ||
> +                   !kvm_irq_is_postable(&irq)) {
>                         /*
>                          * Make sure the IRTE is in remapped mode if
>                          * we don't handle it in posted mode.
> --
> 2.17.1
>
>
>
>
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