KVM: x86/xen: Kernel acceleration for XENVER_version

Turns out this is a fast path for PV guests because they use it to
trigger the event channel upcall. So letting it bounce all the way up
to userspace is not great.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-14-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 8193d52..f3fba9d 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1026,6 +1026,7 @@ struct msr_bitmap_range {
 
 /* Xen emulation context */
 struct kvm_xen {
+       u32 xen_version;
        bool long_mode;
        u8 upcall_vector;
        struct gfn_to_pfn_cache shinfo_cache;

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 0e1595d..98438f2 100644 (file)
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -18,6 +18,7 @@
 #include <trace/events/kvm.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/vcpu.h>
+#include <xen/interface/version.h>
 #include <xen/interface/event_channel.h>
 #include <xen/interface/sched.h>
 
@@ -465,6 +466,13 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
                r = kvm_xen_setattr_evtchn(kvm, data);
                break;
 
+       case KVM_XEN_ATTR_TYPE_XEN_VERSION:
+               mutex_lock(&kvm->lock);
+               kvm->arch.xen.xen_version = data->u.xen_version;
+               mutex_unlock(&kvm->lock);
+               r = 0;
+               break;
+
        default:
                break;
        }
@@ -497,6 +505,11 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
                r = 0;
                break;
 
+       case KVM_XEN_ATTR_TYPE_XEN_VERSION:
+               data->u.xen_version = kvm->arch.xen.xen_version;
+               r = 0;
+               break;
+
        default:
                break;
        }
@@ -1059,6 +1072,12 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
                                params[3], params[4], params[5]);
 
        switch (input) {
+       case __HYPERVISOR_xen_version:
+               if (params[0] == XENVER_version && vcpu->kvm->arch.xen.xen_version) {
+                       r = vcpu->kvm->arch.xen.xen_version;
+                       handled = true;
+               }
+               break;
        case __HYPERVISOR_event_channel_op:
                if (params[0] == EVTCHNOP_send)
                        handled = kvm_xen_hcall_evtchn_send(vcpu, params[1], &r);

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index cb223e4..4dda389 100644 (file)
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1711,7 +1711,7 @@ struct kvm_xen_hvm_attr {
                                __u32 padding[4];
                        } deliver;
                } evtchn;
-
+               __u32 xen_version;
                __u64 pad[8];
        } u;
 };
@@ -1722,6 +1722,7 @@ struct kvm_xen_hvm_attr {
 #define KVM_XEN_ATTR_TYPE_UPCALL_VECTOR                0x2
 /* Available with KVM_CAP_XEN_HVM / KVM_XEN_HVM_CONFIG_EVTCHN_SEND */
 #define KVM_XEN_ATTR_TYPE_EVTCHN               0x3
+#define KVM_XEN_ATTR_TYPE_XEN_VERSION          0x4
 
 /* Per-vCPU Xen attributes */
 #define KVM_XEN_VCPU_GET_ATTR  _IOWR(KVMIO, 0xca, struct kvm_xen_vcpu_attr)