[PATCH 8/8] KVM: xen: automatically use the vcpu_info embedded in shared_info

[Paul Durrant <paul@xen.org>]

From: Paul Durrant <pdurrant@amazon.com>

Add a KVM_XEN_HVM_CONFIG_DEFAULT_VCPU_INFO flag so that the VMM knows it
need only set the KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO attribute in response to
a VCPUOP_register_vcpu_info hypercall, and modify get_vcpu_info_cache()
to pass back a pointer to the shared info pfn cache (and appropriate
offset) for any of the first 32 vCPUs if the attribute has not been set.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org
---
 arch/x86/kvm/x86.c       |  3 ++-
 arch/x86/kvm/xen.c       | 15 +++++++++++++++
 include/uapi/linux/kvm.h |  1 +
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4cd577d01bc4..cdce8c463a1b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4528,7 +4528,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		    KVM_XEN_HVM_CONFIG_SHARED_INFO |
 		    KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL |
 		    KVM_XEN_HVM_CONFIG_EVTCHN_SEND |
-		    KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA;
+		    KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA |
+		    KVM_XEN_HVM_CONFIG_DEFAULT_VCPU_INFO;
 		if (sched_info_on())
 			r |= KVM_XEN_HVM_CONFIG_RUNSTATE |
 			     KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG;
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 892563fea40f..66050a96ba25 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -491,6 +491,21 @@ static void kvm_xen_inject_vcpu_vector(struct kvm_vcpu *v)
 
 struct gfn_to_pfn_cache *get_vcpu_info_cache(struct kvm_vcpu *v, unsigned long *offset)
 {
+	if (!v->arch.xen.vcpu_info_cache.active && v->arch.xen.vcpu_id < MAX_VIRT_CPUS) {
+		struct kvm *kvm = v->kvm;
+
+		if (offset) {
+			if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode)
+				*offset = offsetof(struct shared_info,
+						   vcpu_info[v->arch.xen.vcpu_id]);
+			else
+				*offset = offsetof(struct compat_shared_info,
+						   vcpu_info[v->arch.xen.vcpu_id]);
+		}
+
+		return &kvm->arch.xen.shinfo_cache;
+	}
+
 	if (offset)
 		*offset = 0;
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d3f371bafad8..480612f73fc2 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1283,6 +1283,7 @@ struct kvm_x86_mce {
 #define KVM_XEN_HVM_CONFIG_EVTCHN_SEND		(1 << 5)
 #define KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG	(1 << 6)
 #define KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA	(1 << 7)
+#define KVM_XEN_HVM_CONFIG_DEFAULT_VCPU_INFO	(1 << 8)
 
 struct kvm_xen_hvm_config {
 	__u32 flags;
-- 
2.39.2