[PATCH 5/6] kvm: create per-vcpu dirs in debugfs

[Luiz Capitulino]

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 <lcapitul...@redhat.com>
---
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5486ff9..01c0b9c 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 c1dc45e..c598915 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:
-- 
2.5.5