kvm: embed vcpu id to dentry of vcpu anon inode

Web:        https://git.kernel.org/torvalds/c/e46b469278a59781f9b25ff608af84892963821b
Commit:     e46b469278a59781f9b25ff608af84892963821b
Parent:     a340b3e229b24a56f1c7f5826b15a3af0f4b13e5
Refname:    refs/heads/master
Author:     Masatake YAMATO <[email protected]>
AuthorDate: Sat Jan 20 04:04:22 2018 +0900
Committer:  Radim Krčmář <[email protected]>
CommitDate: Wed Jan 31 18:25:34 2018 +0100

    kvm: embed vcpu id to dentry of vcpu anon inode
    
    All d-entries for vcpu have the same, "anon_inode:kvm-vcpu". That means
    it is impossible to know the mapping between fds for vcpu and vcpu
    from userland.
    
        # LC_ALL=C ls -l /proc/617/fd | grep vcpu
        lrwx------. 1 qemu qemu 64 Jan  7 16:50 18 -> anon_inode:kvm-vcpu
        lrwx------. 1 qemu qemu 64 Jan  7 16:50 19 -> anon_inode:kvm-vcpu
    
    It is also impossible to know the mapping between vma for kvm_run
    structure and vcpu from userland.
    
        # LC_ALL=C grep vcpu /proc/617/maps
        7f9d842d0000-7f9d842d3000 rw-s 00000000 00:0d 20393                      anon_inode:kvm-vcpu
        7f9d842d3000-7f9d842d6000 rw-s 00000000 00:0d 20393                      anon_inode:kvm-vcpu
    
    This change adds vcpu id to d-entries for vcpu. With this change
    you can get the following output:
    
        # LC_ALL=C ls -l /proc/617/fd | grep vcpu
        lrwx------. 1 qemu qemu 64 Jan  7 16:50 18 -> anon_inode:kvm-vcpu:0
        lrwx------. 1 qemu qemu 64 Jan  7 16:50 19 -> anon_inode:kvm-vcpu:1
    
        # LC_ALL=C grep vcpu /proc/617/maps
        7f9d842d0000-7f9d842d3000 rw-s 00000000 00:0d 20393                      anon_inode:kvm-vcpu:0
        7f9d842d3000-7f9d842d6000 rw-s 00000000 00:0d 20393                      anon_inode:kvm-vcpu:1
    
    With the mappings known from the output, a tool like strace can report more details
    of qemu-kvm process activities. Here is the strace output of my local prototype:
    
        # ./strace -KK -f -p 617 2>&1 | grep 'KVM_RUN\| K'
        ...
        [pid   664] ioctl(18, KVM_RUN, 0)       = 0 (KVM_EXIT_MMIO)
         K ready_for_interrupt_injection=1, if_flag=0, flags=0, cr8=0000000000000000, apic_base=0x000000fee00d00
         K phys_addr=0, len=1634035803, [33, 0, 0, 0, 0, 0, 0, 0], is_write=112
        [pid   664] ioctl(18, KVM_RUN, 0)       = 0 (KVM_EXIT_MMIO)
         K ready_for_interrupt_injection=1, if_flag=1, flags=0, cr8=0000000000000000, apic_base=0x000000fee00d00
         K phys_addr=0, len=1634035803, [33, 0, 0, 0, 0, 0, 0, 0], is_write=112
        ...
    
    Signed-off-by: Masatake YAMATO <[email protected]>
    Acked-by: Christian Borntraeger <[email protected]>
    Signed-off-by: Radim Krčmář <[email protected]>
---
 virt/kvm/kvm_main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8af42eab126d..8a937b7cde35 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2415,7 +2415,10 @@ static struct file_operations kvm_vcpu_fops = {
  */
 static int create_vcpu_fd(struct kvm_vcpu *vcpu)
 {
-	return anon_inode_getfd("kvm-vcpu", &kvm_vcpu_fops, vcpu, O_RDWR | O_CLOEXEC);
+	char name[8 + 1 + ITOA_MAX_LEN + 1];
+
+	snprintf(name, sizeof(name), "kvm-vcpu:%d", vcpu->vcpu_id);
+	return anon_inode_getfd(name, &kvm_vcpu_fops, vcpu, O_RDWR | O_CLOEXEC);
 }
 
 static int kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
--
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