[PATCH v4 07/16] KVM: x86/xen: register shared_info page

[David Woodhouse <dwmw2@infradead.org>]

From: Joao Martins <joao.m.martins@oracle.com>

We add a new ioctl, XEN_HVM_SHARED_INFO, to allow hypervisor
to know where the guest's shared info page is.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/xen.c              | 27 +++++++++++++++++++++++++++
 include/uapi/linux/kvm.h        |  4 ++++
 3 files changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4fcb27a9fe36..e48dac4f0359 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -897,6 +897,8 @@ struct msr_bitmap_range {
 /* Xen emulation context */
 struct kvm_xen {
 	bool long_mode;
+	bool shinfo_set;
+	struct gfn_to_hva_cache shinfo_cache;
 };
 
 enum kvm_irqchip_mode {
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 52cb9e465542..9dd9c42842b8 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -13,9 +13,23 @@
 #include <linux/kvm_host.h>
 
 #include <trace/events/kvm.h>
+#include <xen/interface/xen.h>
 
 #include "trace.h"
 
+static int kvm_xen_shared_info_init(struct kvm *kvm, gfn_t gfn)
+{
+	int ret;
+
+	ret = kvm_gfn_to_hva_cache_init(kvm, &kvm->arch.xen.shinfo_cache,
+					gfn_to_gpa(gfn), PAGE_SIZE);
+	if (ret)
+		return ret;
+
+	kvm->arch.xen.shinfo_set = true;
+	return 0;
+}
+
 int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 {
 	int r = -ENOENT;
@@ -28,6 +42,11 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		kvm->arch.xen.long_mode = !!data->u.long_mode;
 		r = 0;
 		break;
+
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
+		r = kvm_xen_shared_info_init(kvm, data->u.shared_info.gfn);
+		break;
+
 	default:
 		break;
 	}
@@ -44,6 +63,14 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		data->u.long_mode = kvm->arch.xen.long_mode;
 		r = 0;
 		break;
+
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
+		if (kvm->arch.xen.shinfo_set) {
+			data->u.shared_info.gfn = gpa_to_gfn(kvm->arch.xen.shinfo_cache.gpa);
+			r = 0;
+		}
+		break;
+
 	default:
 		break;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index b7cf887c8e4d..a47097b90fe8 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1591,11 +1591,15 @@ struct kvm_xen_hvm_attr {
 
 	union {
 		__u8 long_mode;
+		struct {
+			__u64 gfn;
+		} shared_info;
 		__u64 pad[4];
 	} u;
 };
 
 #define KVM_XEN_ATTR_TYPE_LONG_MODE		0x0
+#define KVM_XEN_ATTR_TYPE_SHARED_INFO		0x1
 
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {
-- 
2.29.2