KVM: x86/xen: Support per-vCPU event channel upcall via local APIC

Windows uses a per-vCPU vector, and it's delivered via the local APIC
basically like an MSI (with associated EOI) unlike the traditional
guest-wide vector which is just magically asserted by Xen (and in the
KVM case by kvm_xen_has_interrupt() / kvm_cpu_get_extint()).

Now that the kernel is able to raise event channel events for itself,
being able to do so for Windows guests is also going to be useful.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-15-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f3fba9d8ddc6930e2524dad73f15d10301fee72e..998caf7a3ce96f4860a91ec1af9aec5e7a62c7f2 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -606,6 +606,7 @@ struct kvm_vcpu_hv {
 struct kvm_vcpu_xen {
        u64 hypercall_rip;
        u32 current_runstate;
+       u8 upcall_vector;
        struct gfn_to_pfn_cache vcpu_info_cache;
        struct gfn_to_pfn_cache vcpu_time_info_cache;
        struct gfn_to_pfn_cache runstate_cache;

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 98438f27f6b399290b6baf86564f535c9e1a3faa..5afaf7b59944b702405e4cd85fadc81de27d2d24 100644 (file)
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -314,6 +314,22 @@ void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, int state)
        mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
 }
 
+static void kvm_xen_inject_vcpu_vector(struct kvm_vcpu *v)
+{
+       struct kvm_lapic_irq irq = { };
+       int r;
+
+       irq.dest_id = v->vcpu_id;
+       irq.vector = v->arch.xen.upcall_vector;
+       irq.dest_mode = APIC_DEST_PHYSICAL;
+       irq.shorthand = APIC_DEST_NOSHORT;
+       irq.delivery_mode = APIC_DM_FIXED;
+       irq.level = 1;
+
+       /* The fast version will always work for physical unicast */
+       WARN_ON_ONCE(!kvm_irq_delivery_to_apic_fast(v->kvm, NULL, &irq, &r, NULL));
+}
+
 /*
  * On event channel delivery, the vcpu_info may not have been accessible.
  * In that case, there are bits in vcpu->arch.xen.evtchn_pending_sel which
@@ -374,6 +390,10 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
        }
        read_unlock_irqrestore(&gpc->lock, flags);
 
+       /* For the per-vCPU lapic vector, deliver it as MSI. */
+       if (v->arch.xen.upcall_vector)
+               kvm_xen_inject_vcpu_vector(v);
+
        mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
 }
 
@@ -708,6 +728,15 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
                r = 0;
                break;
 
+       case KVM_XEN_VCPU_ATTR_TYPE_UPCALL_VECTOR:
+               if (data->u.vector && data->u.vector < 0x10)
+                       r = -EINVAL;
+               else {
+                       vcpu->arch.xen.upcall_vector = data->u.vector;
+                       r = 0;
+               }
+               break;
+
        default:
                break;
        }
@@ -795,6 +824,11 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
                r = 0;
                break;
 
+       case KVM_XEN_VCPU_ATTR_TYPE_UPCALL_VECTOR:
+               data->u.vector = vcpu->arch.xen.upcall_vector;
+               r = 0;
+               break;
+
        default:
                break;
        }
@@ -1228,6 +1262,12 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, struct kvm *kvm)
                                kick_vcpu = true;
                        }
                }
+
+               /* For the per-vCPU lapic vector, deliver it as MSI. */
+               if (kick_vcpu && vcpu->arch.xen.upcall_vector) {
+                       kvm_xen_inject_vcpu_vector(vcpu);
+                       kick_vcpu = false;
+               }
        }
 
  out_rcu:

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 4dda3896ed715c97699467d343d8e21eeae94244..a9ba690c4f3756ee698198927f45042c18ed8f4e 100644 (file)
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1754,6 +1754,7 @@ struct kvm_xen_vcpu_attr {
                        __u32 priority;
                        __u64 expires_ns;
                } timer;
+               __u8 vector;
        } u;
 };
 
@@ -1767,6 +1768,7 @@ struct kvm_xen_vcpu_attr {
 /* Available with KVM_CAP_XEN_HVM / KVM_XEN_HVM_CONFIG_EVTCHN_SEND */
 #define KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID         0x6
 #define KVM_XEN_VCPU_ATTR_TYPE_TIMER           0x7
+#define KVM_XEN_VCPU_ATTR_TYPE_UPCALL_VECTOR   0x8
 
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {