kvm: create per-vcpu dirs in debugfs

This commit adds the ability for archs to export
per-vcpu information via a new per-vcpu dir in
the VM's debugfs directory.

If kvm_arch_has_vcpu_debugfs() returns true, then KVM
will create a vcpu dir for each vCPU in the VM's
debugfs directory. Then kvm_arch_create_vcpu_debugfs()
is responsible for populating each vcpu directory
with arch specific entries.

The per-vcpu path in debugfs will look like:

/sys/kernel/debug/kvm/29162-10/vcpu0
/sys/kernel/debug/kvm/29162-10/vcpu1

This is all arch specific for now because the only
user of this interface (x86) wants to export x86-specific
per-vcpu information to user-space.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 33 insertions, 0 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5486ff9aa71e..01c0b9cc3915 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -265,6 +265,7 @@ struct kvm_vcpu {
 #endif
         bool preempted;
         struct kvm_vcpu_arch arch;
+        struct dentry *debugfs_dentry;
 };
 
 static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a6e864c67e35..81dfc73d3df3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2371,6 +2371,7 @@ static int kvm_vcpu_release(struct inode *inode, struct file *filp)
 {
         struct kvm_vcpu *vcpu = filp->private_data;
 
+        debugfs_remove_recursive(vcpu->debugfs_dentry);
         kvm_put_kvm(vcpu->kvm);
         return 0;
 }
@@ -2393,6 +2394,32 @@ static int create_vcpu_fd(struct kvm_vcpu *vcpu)
         return anon_inode_getfd("kvm-vcpu", &kvm_vcpu_fops, vcpu, O_RDWR | O_CLOEXEC);
 }
 
+static int kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
+{
+        char dir_name[ITOA_MAX_LEN * 2];
+        int ret;
+
+        if (!kvm_arch_has_vcpu_debugfs())
+                return 0;
+
+        if (!debugfs_initialized())
+                return 0;
+
+        snprintf(dir_name, sizeof(dir_name), "vcpu%d", vcpu->vcpu_id);
+        vcpu->debugfs_dentry = debugfs_create_dir(dir_name,
+                                                                vcpu->kvm->debugfs_dentry);
+        if (!vcpu->debugfs_dentry)
+                return -ENOMEM;
+
+        ret = kvm_arch_create_vcpu_debugfs(vcpu);
+        if (ret < 0) {
+                debugfs_remove_recursive(vcpu->debugfs_dentry);
+                return ret;
+        }
+
+        return 0;
+}
+
 /*
  * Creates some virtual cpus.  Good luck creating more than one.
  */
@@ -2425,6 +2452,10 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
         if (r)
                 goto vcpu_destroy;
 
+        r = kvm_create_vcpu_debugfs(vcpu);
+        if (r)
+                goto vcpu_destroy;
+
         mutex_lock(&kvm->lock);
         if (kvm_get_vcpu_by_id(kvm, id)) {
                 r = -EEXIST;
@@ -2456,6 +2487,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 
 unlock_vcpu_destroy:
         mutex_unlock(&kvm->lock);
+        debugfs_remove_recursive(vcpu->debugfs_dentry);
 vcpu_destroy:
         kvm_arch_vcpu_destroy(vcpu);
 vcpu_decrement: