On 07/05/20 04:14, Like Xu wrote:
> +static inline u64 vmx_get_perf_capabilities(void)
> +{
> + u64 perf_cap = 0;
> +
> + if (boot_cpu_has(X86_FEATURE_PDCM))
> + rdmsrl(MSR_IA32_PERF_CAPABILITIES, perf_cap);
> +
> + /* Currently, KVM only supports Full-Width Writes. */
> + perf_cap &= PMU_CAP_FW_WRITES;
> +
> + return perf_cap;
> +}
> +
Since counters are virtualized, it seems to me that you can support
PMU_CAP_FW_WRITES unconditionally, even if the host lacks it. So just
return PMU_CAP_FW_WRITES from this function.
> + case MSR_IA32_PERF_CAPABILITIES:
> + return 1; /* RO MSR */
> default:
You need to allow writes from the host if (data &
~vmx_get_perf_capabilities()) == 0.
> - if (!msr_info->host_initiated)
> + if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
> + (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
> + if (data & ~pmu->counter_bitmask[KVM_PMC_GP])
> + return 1;
> + if (!fw_writes_is_enabled(pmu))
> data = (s64)(s32)data;
You are dropping the test on msr_info->host_initiated here, you should
keep it otherwise you allow full-width write to MSR_IA32_PERFCTR0 as
well. So:
#define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0)
if (!msr_info->host_initiated && !(msr & MSR_PMC_FULL_WIDTH_BIT))
data = (s64)(s32)data;
> + case MSR_IA32_PERF_CAPABILITIES:
> + if (!nested)
> + return 1;
> + msr->data = vmx_get_perf_capabilities();
> + return 0;
The !nested check is wrong.
>
> +++ b/arch/x86/kvm/x86.c
> @@ -1220,6 +1220,13 @@ static const u32 msrs_to_save_all[] = {
> MSR_ARCH_PERFMON_EVENTSEL0 + 12, MSR_ARCH_PERFMON_EVENTSEL0 + 13,
> MSR_ARCH_PERFMON_EVENTSEL0 + 14, MSR_ARCH_PERFMON_EVENTSEL0 + 15,
> MSR_ARCH_PERFMON_EVENTSEL0 + 16, MSR_ARCH_PERFMON_EVENTSEL0 + 17,
> +
> + MSR_IA32_PMC0, MSR_IA32_PMC0 + 1, MSR_IA32_PMC0 + 2,
> + MSR_IA32_PMC0 + 3, MSR_IA32_PMC0 + 4, MSR_IA32_PMC0 + 5,
> + MSR_IA32_PMC0 + 6, MSR_IA32_PMC0 + 7, MSR_IA32_PMC0 + 8,
> + MSR_IA32_PMC0 + 9, MSR_IA32_PMC0 + 10, MSR_IA32_PMC0 + 11,
> + MSR_IA32_PMC0 + 12, MSR_IA32_PMC0 + 13, MSR_IA32_PMC0 + 14,
> + MSR_IA32_PMC0 + 15, MSR_IA32_PMC0 + 16, MSR_IA32_PMC0 + 17,
> };
This is not needed because the full-width content is already accessible
from the host via MSR_IA32_PERFCTRn.
Given the bugs, it is clear that you should also modify the pmu.c
testcase for kvm-unit-tests to cover full-width writes (and especially
the non-full-width write behavior of MSR_IA32_PERFCTRn). Even before
the QEMU side is begin worked on, you can test it with "-cpu
host,migratable=off".
Thanks,
Paolo
