Re: [PATCH v4 05/10] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest
From: Wei Wang
Date: Mon Jan 07 2019 - 04:09:50 EST
On 01/03/2019 11:25 PM, Jim Mattson wrote:
On Wed, Jan 2, 2019 at 11:55 PM Wei Wang <wei.w.wang@xxxxxxxxx> wrote:
Right, thanks. Probably better to change it to below:
This still breaks backwards compatibility. Returning 0 and raising #GP
msr_info->data = 0;
data = native_read_msr(MSR_IA32_PERF_CAPABILITIES);
msr_info->data |= (data & X86_PERF_CAP_MASK_LBR_FMT);
are not the same.
I'm not sure about raising GP# in this case.
This PERF_CAP msr contains more things than the lbr format.
For example, a guest with lbr=false option could read it to get PEBS_FMT,
which is PERF_CAP[11:8]. We should offer those bits in this case.
When lbr=false, the lbr feature is not usable by the guest,
so I think whatever value (0 or other value) of the LBR_FMT bits that
we give to the guest might not be important.