[PATCH v2 02/11] KVM: introduce new vendor op for KVM_GET_DEVICE_ATTR

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

Allow vendor modules to provide their own attributes on /dev/kvm.
To avoid proliferation of vendor ops, implement KVM_HAS_DEVICE_ATTR
and KVM_GET_DEVICE_ATTR in terms of the same function.  You're not
supposed to use KVM_GET_DEVICE_ATTR to do complicated computations,
especially on /dev/kvm.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Message-Id: <20240209183743.22030-3-pbonzini@xxxxxxxxxx>
Reviewed-by: Michael Roth <michael.roth@xxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm-x86-ops.h |  1 +
 arch/x86/include/asm/kvm_host.h    |  1 +
 arch/x86/kvm/x86.c                 | 52 +++++++++++++++++++-----------
 3 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 378ed944b849..ac8b7614e79d 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -122,6 +122,7 @@ KVM_X86_OP(enter_smm)
 KVM_X86_OP(leave_smm)
 KVM_X86_OP(enable_smi_window)
 #endif
+KVM_X86_OP_OPTIONAL(dev_get_attr)
 KVM_X86_OP_OPTIONAL(mem_enc_ioctl)
 KVM_X86_OP_OPTIONAL(mem_enc_register_region)
 KVM_X86_OP_OPTIONAL(mem_enc_unregister_region)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d271ba20a0b2..0bcd9ae16097 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1769,6 +1769,7 @@ struct kvm_x86_ops {
 	void (*enable_smi_window)(struct kvm_vcpu *vcpu);
 #endif
 
+	int (*dev_get_attr)(u64 attr, u64 *val);
 	int (*mem_enc_ioctl)(struct kvm *kvm, void __user *argp);
 	int (*mem_enc_register_region)(struct kvm *kvm, struct kvm_enc_region *argp);
 	int (*mem_enc_unregister_region)(struct kvm *kvm, struct kvm_enc_region *argp);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bf10a9073a09..8746530930d5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4804,37 +4804,53 @@ static inline void __user *kvm_get_attr_addr(struct kvm_device_attr *attr)
 	return uaddr;
 }
 
-static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
+static int __kvm_x86_dev_get_attr(struct kvm_device_attr *attr, u64 *val)
 {
-	u64 __user *uaddr = kvm_get_attr_addr(attr);
+	int r;
 
 	if (attr->group)
 		return -ENXIO;
 
+	switch (attr->attr) {
+	case KVM_X86_XCOMP_GUEST_SUPP:
+		r = 0;
+		*val = kvm_caps.supported_xcr0;
+		break;
+	default:
+		r = -ENXIO;
+		if (kvm_x86_ops.dev_get_attr)
+			r = kvm_x86_ops.dev_get_attr(attr->attr, val);
+		break;
+	}
+
+	return r;
+}
+
+static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
+{
+	u64 __user *uaddr;
+	int r;
+	u64 val;
+
+	r = __kvm_x86_dev_get_attr(attr, &val);
+	if (r < 0)
+		return r;
+
+	uaddr = kvm_get_attr_addr(attr);
 	if (IS_ERR(uaddr))
 		return PTR_ERR(uaddr);
 
-	switch (attr->attr) {
-	case KVM_X86_XCOMP_GUEST_SUPP:
-		if (put_user(kvm_caps.supported_xcr0, uaddr))
-			return -EFAULT;
-		return 0;
-	default:
-		return -ENXIO;
-	}
+	if (put_user(val, uaddr))
+		return -EFAULT;
+
+	return 0;
 }
 
 static int kvm_x86_dev_has_attr(struct kvm_device_attr *attr)
 {
-	if (attr->group)
-		return -ENXIO;
+	u64 val;
 
-	switch (attr->attr) {
-	case KVM_X86_XCOMP_GUEST_SUPP:
-		return 0;
-	default:
-		return -ENXIO;
-	}
+	return __kvm_x86_dev_get_attr(attr, &val);
 }
 
 long kvm_arch_dev_ioctl(struct file *filp,
-- 
2.39.1