KVM: stats: Support binary stats retrieval for a VCPU

Add a VCPU ioctl to get a statistics file descriptor by which a read
functionality is provided for userspace to read out VCPU stats header,
descriptors and data.
Define VCPU statistics descriptors and header for all architectures.

Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com> #arm64
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Message-Id: <20210618222709.1858088-5-jingzhangos@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 50 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 33ec43a87d0f..c8d0028df4ac 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3448,6 +3448,10 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 	vcpu->vcpu_idx = atomic_read(&kvm->online_vcpus);
 	BUG_ON(kvm->vcpus[vcpu->vcpu_idx]);
 
+	/* Fill the stats id string for the vcpu */
+	snprintf(vcpu->stats_id, sizeof(vcpu->stats_id), "kvm-%d/vcpu-%d",
+		 task_pid_nr(current), id);
+
 	/* Now it's all set up, let userspace reach it */
 	kvm_get_kvm(kvm);
 	r = create_vcpu_fd(vcpu);
@@ -3497,6 +3501,44 @@ static int kvm_vcpu_ioctl_set_sigmask(struct kvm_vcpu *vcpu, sigset_t *sigset)
 	return 0;
 }
 
+static ssize_t kvm_vcpu_stats_read(struct file *file, char __user *user_buffer,
+			      size_t size, loff_t *offset)
+{
+	struct kvm_vcpu *vcpu = file->private_data;
+
+	return kvm_stats_read(vcpu->stats_id, &kvm_vcpu_stats_header,
+			&kvm_vcpu_stats_desc[0], &vcpu->stat,
+			sizeof(vcpu->stat), user_buffer, size, offset);
+}
+
+static const struct file_operations kvm_vcpu_stats_fops = {
+	.read = kvm_vcpu_stats_read,
+	.llseek = noop_llseek,
+};
+
+static int kvm_vcpu_ioctl_get_stats_fd(struct kvm_vcpu *vcpu)
+{
+	int fd;
+	struct file *file;
+	char name[15 + ITOA_MAX_LEN + 1];
+
+	snprintf(name, sizeof(name), "kvm-vcpu-stats:%d", vcpu->vcpu_id);
+
+	fd = get_unused_fd_flags(O_CLOEXEC);
+	if (fd < 0)
+		return fd;
+
+	file = anon_inode_getfile(name, &kvm_vcpu_stats_fops, vcpu, O_RDONLY);
+	if (IS_ERR(file)) {
+		put_unused_fd(fd);
+		return PTR_ERR(file);
+	}
+	file->f_mode |= FMODE_PREAD;
+	fd_install(fd, file);
+
+	return fd;
+}
+
 static long kvm_vcpu_ioctl(struct file *filp,
 			   unsigned int ioctl, unsigned long arg)
 {
@@ -3694,6 +3736,10 @@ out_free1:
 		r = kvm_arch_vcpu_ioctl_set_fpu(vcpu, fpu);
 		break;
 	}
+	case KVM_GET_STATS_FD: {
+		r = kvm_vcpu_ioctl_get_stats_fd(vcpu);
+		break;
+	}
 	default:
 		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
 	}
@@ -3952,6 +3998,8 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 #else
 		return 0;
 #endif
+	case KVM_CAP_BINARY_STATS_FD:
+		return 1;
 	default:
 		break;
 	}
@@ -5254,7 +5302,8 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 		kmem_cache_create_usercopy("kvm_vcpu", vcpu_size, vcpu_align,
 					   SLAB_ACCOUNT,
 					   offsetof(struct kvm_vcpu, arch),
-					   sizeof_field(struct kvm_vcpu, arch),
+					   offsetofend(struct kvm_vcpu, stats_id)
+					   - offsetof(struct kvm_vcpu, arch),
 					   NULL);
 	if (!kvm_vcpu_cache) {
 		r = -ENOMEM;