[PATCH 0/4] kvm: export TSC offset to user-space

[Luiz Capitulino]

Hi,

We need to retrieve a VM's TSC offset in order to use
the host's TSC to merge host and guest traces. This is
explained in detail in this thread:

  [Qemu-devel] [RFC] host and guest kernel trace merging
  https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg00887.html

Today, the only way to retrieve a VM's TSC offset is
by using the kvm_write_tsc_offset tracepoint. This has
a few problems. First, the tracepoint is only emitted
when the VM boots, which requires a reboot to get it if
the VM is already running. Second, tracepoints are not
supposed to be ABIs in case they need to be consumed by
user-space tools.

This series exports a VM's TSC offset to user-space via
debugfs. A new file called "tsc-offset" is created in
the VM's debugfs directory. For example:

  /sys/kernel/debug/kvm/51696-10/tsc-offset

This file contains one TSC offset per line, for each
vCPU. For example:

  vcpu0: 18446742405270834952
  vcpu1: 18446742405270834952
  vcpu2: 18446742405270834952
  vcpu3: 18446742405270834952

Please, see patch 4/4 for additional details.

Luiz Capitulino (4):
  kvm: kvm_destroy_vm_debugfs(): check debugs_stat_data pointer
  kvm: kvm_create_vm_debugfs(): cleanup on error
  kvm: add stub for arch specific debugfs support
  kvm: x86: export TSC offset to user-space

 arch/arm/kvm/arm.c              |  5 +++++
 arch/mips/kvm/mips.c            |  5 +++++
 arch/powerpc/kvm/powerpc.c      |  5 +++++
 arch/s390/kvm/kvm-s390.c        |  5 +++++
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/svm.c              |  1 +
 arch/x86/kvm/vmx.c              |  8 ++++++++
 arch/x86/kvm/x86.c              | 35 +++++++++++++++++++++++++++++++++++
 include/linux/kvm_host.h        |  2 ++
 virt/kvm/kvm_main.c             | 22 ++++++++++++++++------
 10 files changed, 83 insertions(+), 6 deletions(-)

-- 
2.5.5