[RFC v3 0/2] add bus lock VM exit support

From: Chenyi Qiang
Date: Thu Sep 10 2020 - 04:37:03 EST

v2->v3 changelogs:
- use a bitmap to get/set the capability of bus lock detection. we support
exit and off mode currently.
- put the handle of exiting to userspace in vmx.c, thus no need to
define a shadow to track vmx->exit_reason.bus_lock_detected.
- remove the vcpu->stats.bus_locks since every bus lock exits to userspace.


Add the support for bus lock VM exit in KVM. It is a sub-feature of bus
lock detection and the detailed info can be found in the patch 2/2.

In this patch series, the first patch applies Sean's refactor to
vcpu_vmx.exit_reason available at
It is necessary as bus lock VM exit adds a new modifier bit(bit 26) in
exit_reason field in VMCS.

The second patch is the enabling work for bus lock VM exit. Add the
support to set the capability to enable bus lock vm exit. The current
implementation just exit to user space when handling the bus lock
detected in guest.

The concrete throttling policy in user space still needs to be
discussed. We can enforce ratelimit on bus lock in guest, just inject
some sleep time, or maybe other ideas.

Document for Bus Lock Detection is now available at the latest "Intel
Architecture Instruction Set Extensions Programming Reference" (see
below). Note that the section 9.1 for Bus Lock Debug Exception requires
modification due to the feedback from kernel community:

Document Link:

Chenyi Qiang (1):
KVM: VMX: Enable bus lock VM exit

Sean Christopherson (1):
KVM: VMX: Convert vcpu_vmx.exit_reason to a union

arch/x86/include/asm/kvm_host.h | 5 ++
arch/x86/include/asm/vmx.h | 1 +
arch/x86/include/asm/vmxfeatures.h | 1 +
arch/x86/include/uapi/asm/kvm.h | 1 +
arch/x86/include/uapi/asm/vmx.h | 4 +-
arch/x86/kvm/vmx/capabilities.h | 6 ++
arch/x86/kvm/vmx/nested.c | 42 ++++++++----
arch/x86/kvm/vmx/vmx.c | 106 ++++++++++++++++++++---------
arch/x86/kvm/vmx/vmx.h | 25 ++++++-
arch/x86/kvm/x86.c | 27 +++++++-
arch/x86/kvm/x86.h | 5 ++
include/uapi/linux/kvm.h | 7 ++
12 files changed, 179 insertions(+), 51 deletions(-)