There is one bug in KVM that can hit vm-entry failure 100% on platform
supporting PT_MODE_HOST_GUEST mode following below steps:
1. #modprobe -r kvm_intel
2. #modprobe kvm_intel pt_mode=1
3. start a VM with QEMU
4. on host: #perf record -e intel_pt//
The vm-entry failure happens because it violates the requirement stated
in Intel SDM 26.2.1.1 VM-Execution Control Fields
If the logical processor is operating with Intel PT enabled (if
IA32_RTIT_CTL.TraceEn = 1) at the time of VM entry, the "load
IA32_RTIT_CTL" VM-entry control must be 0.
On PT_MODE_HOST_GUEST node, vm-entry load RTIT is always set. Thus KVM
needs to ensure IA32_RTIT_CTL.TraceEn is 0 before VM-entry. Currently KVM
manually WRMSR(IA32_RTIT_CTL) to clear TraceEn bit. However, it doesn't
work everytime since there is a posibility that IA32_RTIT_CTL.TraceEn is
re-enabled in PT PMI handler before vm-entry.
This series tries to fix the issue by exposing and calling perf driver
API to stop host PT event (if any) before vm-entry and resume PT event
after vm-exit. Perf API can prevent PT PMI handler from re-enabling PT.
By the way, drop the save/restore of PT MSRs of host because the resume
of PT event after vm-exit doesn't rely on the previous value of PT MSRs.
Changes in v1:
- Export perf_event_{en,dis}able_local() and pt_get_curr_event() for KVM to
stop/resume PT event; (Suggested-by Wang, Wei W <wei.w.wang@xxxxxxxxx>)
- Drop the save/restore of host PT MSRs.
v1: https://lore.kernel.org/all/20220825085625.867763-1-xiaoyao.li@xxxxxxxxx/
Xiaoyao Li (3):
perf/core: Expose perf_event_{en,dis}able_local()
perf/x86/intel/pt: Introduce and export pt_get_curr_event()
KVM: VMX: Stop/resume host PT before/after VMX transition when
PT_MODE_HOST_GUEST
arch/x86/events/intel/pt.c | 8 ++++++++
arch/x86/include/asm/perf_event.h | 2 ++
arch/x86/kvm/vmx/vmx.c | 31 +++++++++++++------------------
arch/x86/kvm/vmx/vmx.h | 2 +-
include/linux/perf_event.h | 1 +
kernel/events/core.c | 7 +++++++
6 files changed, 32 insertions(+), 19 deletions(-)
--
2.27.0
