Re: [RESEND PATCH v4 04/10] KVM: vmx/pmu: Add MSR_ARCH_LBR_CTL emulation for Arch LBR

[Jim Mattson]

On Mon, May 10, 2021 at 1:16 AM Like Xu <like.xu@xxxxxxxxxxxxxxx> wrote:
>
> Arch LBRs are enabled by setting MSR_ARCH_LBR_CTL.LBREn to 1. A new guest
> state field named "Guest IA32_LBR_CTL" is added to enhance guest LBR usage.
> When guest Arch LBR is enabled, a guest LBR event will be created like the
> model-specific LBR does.
>
> On processors that support Arch LBR, MSR_IA32_DEBUGCTLMSR[bit 0] has no
> meaning. It can be written to 0 or 1, but reads will always return 0.
> Like IA32_DEBUGCTL, IA32_ARCH_LBR_CTL msr is also reserved on INIT.
>
> Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/events/intel/lbr.c      |  2 --
>  arch/x86/include/asm/msr-index.h |  1 +
>  arch/x86/include/asm/vmx.h       |  2 ++
>  arch/x86/kvm/vmx/pmu_intel.c     | 31 ++++++++++++++++++++++++++-----
>  arch/x86/kvm/vmx/vmx.c           |  9 +++++++++
>  5 files changed, 38 insertions(+), 7 deletions(-)
>
Same comments as on the previous patch. Your guard for ensuring that
the new VMCS fields exist can be spoofed by a malicious userspace, and
the new MSR has to be enumerated by KVM_GET_MSR_INDEX_LIST.