On 01/19/2018 08:04 PM, Masatake YAMATO wrote:
> 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 <yamato@xxxxxxxxxx>
I like that idea a lot. In debugging sessions I often lookup /proc/*/fd/*.
Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> ---
> 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 210bf820385a..e1e119865247 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2418,7 +2418,10 @@ 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)
>
