[PATCH RFC 03/39] KVM: x86/xen: register shared_info page

[Joao Martins]

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@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  3 +++
 arch/x86/kvm/x86.c              | 21 +++++++++++++++
 arch/x86/kvm/xen.c              | 60 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/xen.h              |  4 +++
 include/uapi/linux/kvm.h        | 15 +++++++++++
 5 files changed, 103 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0f469ce439c0..befc0e37f162 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -843,6 +843,9 @@ struct kvm_hv {
 /* Xen emulation context */
 struct kvm_xen {
 	u64 xen_hypercall;
+
+	gfn_t shinfo_addr;
+	struct shared_info *shinfo;
 };
 
 enum kvm_irqchip_mode {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index be8def385e3f..1eda96304180 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4793,6 +4793,26 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		r = 0;
 		break;
 	}
+	case KVM_XEN_HVM_GET_ATTR: {
+		struct kvm_xen_hvm_attr xha;
+
+		r = -EFAULT;
+		if (copy_from_user(&xha, argp, sizeof(xha)))
+			goto out;
+		r = kvm_xen_hvm_get_attr(kvm, &xha);
+		if (copy_to_user(argp, &xha, sizeof(xha)))
+			goto out;
+		break;
+	}
+	case KVM_XEN_HVM_SET_ATTR: {
+		struct kvm_xen_hvm_attr xha;
+
+		r = -EFAULT;
+		if (copy_from_user(&xha, argp, sizeof(xha)))
+			goto out;
+		r = kvm_xen_hvm_set_attr(kvm, &xha);
+		break;
+	}
 	case KVM_SET_CLOCK: {
 		struct kvm_clock_data user_ns;
 		u64 now_ns;
@@ -9279,6 +9299,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 	kvm_mmu_uninit_vm(kvm);
 	kvm_page_track_cleanup(kvm);
 	kvm_hv_destroy_vm(kvm);
+	kvm_xen_destroy_vm(kvm);
 }
 
 void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *free,
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 76f0e4b812d2..4df223bd3cd7 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -11,9 +11,61 @@
 #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)
+{
+	struct shared_info *shared_info;
+	struct page *page;
+
+	page = gfn_to_page(kvm, gfn);
+	if (is_error_page(page))
+		return -EINVAL;
+
+	kvm->arch.xen.shinfo_addr = gfn;
+
+	shared_info = page_to_virt(page);
+	memset(shared_info, 0, sizeof(struct shared_info));
+	kvm->arch.xen.shinfo = shared_info;
+	return 0;
+}
+
+int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
+{
+	int r = -ENOENT;
+
+	switch (data->type) {
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO: {
+		gfn_t gfn = data->u.shared_info.gfn;
+
+		r = kvm_xen_shared_info_init(kvm, gfn);
+		break;
+	}
+	default:
+		break;
+	}
+
+	return r;
+}
+
+int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
+{
+	int r = -ENOENT;
+
+	switch (data->type) {
+	case KVM_XEN_ATTR_TYPE_SHARED_INFO: {
+		data->u.shared_info.gfn = kvm->arch.xen.shinfo_addr;
+		break;
+	}
+	default:
+		break;
+	}
+
+	return r;
+}
+
 bool kvm_xen_hypercall_enabled(struct kvm *kvm)
 {
 	return READ_ONCE(kvm->arch.xen.xen_hypercall);
@@ -77,3 +129,11 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
 
 	return 0;
 }
+
+void kvm_xen_destroy_vm(struct kvm *kvm)
+{
+	struct kvm_xen *xen = &kvm->arch.xen;
+
+	if (xen->shinfo)
+		put_page(virt_to_page(xen->shinfo));
+}
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index a2ae079c3ef3..bb38edf383fe 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -3,8 +3,12 @@
 #ifndef __ARCH_X86_KVM_XEN_H__
 #define __ARCH_X86_KVM_XEN_H__
 
+int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
+int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
 bool kvm_xen_hypercall_enabled(struct kvm *kvm);
 bool kvm_xen_hypercall_set(struct kvm *kvm);
 int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
 
+void kvm_xen_destroy_vm(struct kvm *kvm);
+
 #endif
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d07520c216a1..de2168d235af 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1455,6 +1455,21 @@ struct kvm_enc_region {
 /* Available with KVM_CAP_HYPERV_CPUID */
 #define KVM_GET_SUPPORTED_HV_CPUID _IOWR(KVMIO, 0xc1, struct kvm_cpuid2)
 
+#define KVM_XEN_HVM_GET_ATTR        _IOWR(KVMIO,  0xc2, struct kvm_xen_hvm_attr)
+#define KVM_XEN_HVM_SET_ATTR        _IOW(KVMIO,  0xc3, struct kvm_xen_hvm_attr)
+
+struct kvm_xen_hvm_attr {
+	__u16 type;
+
+	union {
+		struct {
+			__u64 gfn;
+		} shared_info;
+	} u;
+};
+
+#define KVM_XEN_ATTR_TYPE_SHARED_INFO       0x0
+
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {
 	/* Guest initialization commands */
-- 
2.11.0