On Thu, Aug 01, 2024, Mingwei Zhang wrote:
> Add nested virtualization support for passthrough PMU by combining the MSR
> interception bitmaps of vmcs01 and vmcs12. Readers may argue even without
> this patch, nested virtualization works for passthrough PMU because L1 will
> see Perfmon v2 and will have to use legacy vPMU implementation if it is
> Linux. However, any assumption made on L1 may be invalid, e.g., L1 may not
> even be Linux.
>
> If both L0 and L1 pass through PMU MSRs, the correct behavior is to allow
> MSR access from L2 directly touch HW MSRs, since both L0 and L1 passthrough
> the access.
>
> However, in current implementation, if without adding anything for nested,
> KVM always set MSR interception bits in vmcs02. This leads to the fact that
> L0 will emulate all MSR read/writes for L2, leading to errors, since the
> current passthrough vPMU never implements set_msr() and get_msr() for any
> counter access except counter accesses from the VMM side.
>
> So fix the issue by setting up the correct MSR interception for PMU MSRs.
>
> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/nested.c | 52 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 52 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 643935a0f70a..ef385f9e7513 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -612,6 +612,55 @@ static inline void nested_vmx_set_intercept_for_msr(struct vcpu_vmx *vmx,
> msr_bitmap_l0, msr);
> }
>
> +/* Pass PMU MSRs to nested VM if L0 and L1 are set to passthrough. */
> +static void nested_vmx_set_passthru_pmu_intercept_for_msr(struct kvm_vcpu *vcpu,
> + unsigned long *msr_bitmap_l1,
> + unsigned long *msr_bitmap_l0)
> +{
> + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> + int i;
> +
> + for (i = 0; i < pmu->nr_arch_gp_counters; i++) {
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_ARCH_PERFMON_EVENTSEL0 + i,
> + MSR_TYPE_RW);
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_IA32_PERFCTR0 + i,
> + MSR_TYPE_RW);
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_IA32_PMC0 + i,
> + MSR_TYPE_RW);
I think we should add (gross) macros to dedup the bulk of this boilerplate, by
referencing the local variables in the macros. Like I said, gross. But I think
it'd be less error prone and easier to read than the copy+paste mess we have today.
E.g. it's easy to miss that only writes are allowed for MSR_IA32_FLUSH_CMD and
MSR_IA32_PRED_CMD, because there's so much boilerplate.
Something like:
#define nested_vmx_merge_msr_bitmaps(msr, type) \
nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0, msr, type)
#define nested_vmx_merge_msr_bitmaps_read(msr) \
nested_vmx_merge_msr_bitmaps(msr, MSR_TYPE_R);
#define nested_vmx_merge_msr_bitmaps_write(msr) \
nested_vmx_merge_msr_bitmaps(msr, MSR_TYPE_W);
#define nested_vmx_merge_msr_bitmaps_rw(msr) \
nested_vmx_merge_msr_bitmaps(msr, MSR_TYPE_RW);
for (i = 0; i < pmu->nr_arch_gp_counters; i++) {
nested_vmx_merge_msr_bitmaps_rw(MSR_ARCH_PERFMON_EVENTSEL0 + i);
nested_vmx_merge_msr_bitmaps_rw(MSR_IA32_PERFCTR0+ i);
nested_vmx_merge_msr_bitmaps_rw(MSR_IA32_PMC0+ i);
}
for (i = 0; i < vcpu_to_pmu(vcpu)->nr_arch_fixed_counters; i++)
nested_vmx_merge_msr_bitmaps_rw(MSR_CORE_PERF_FIXED_CTR_CTRL);
blah blah blah
> + }
> +
> + for (i = 0; i < vcpu_to_pmu(vcpu)->nr_arch_fixed_counters; i++) {
Curly braces are unnecessary.
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_CORE_PERF_FIXED_CTR0 + i,
> + MSR_TYPE_RW);
> + }
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_CORE_PERF_FIXED_CTR_CTRL,
> + MSR_TYPE_RW);
> +
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_CORE_PERF_GLOBAL_STATUS,
> + MSR_TYPE_RW);
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_CORE_PERF_GLOBAL_CTRL,
> + MSR_TYPE_RW);
> + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1,
> + msr_bitmap_l0,
> + MSR_CORE_PERF_GLOBAL_OVF_CTRL,
> + MSR_TYPE_RW);
> +}
> +
> /*
> * Merge L0's and L1's MSR bitmap, return false to indicate that
> * we do not use the hardware.
> @@ -713,6 +762,9 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
> nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
> MSR_IA32_FLUSH_CMD, MSR_TYPE_W);
>
> + if (is_passthrough_pmu_enabled(vcpu))
> + nested_vmx_set_passthru_pmu_intercept_for_msr(vcpu, msr_bitmap_l1, msr_bitmap_l0);
Please wrap. Or better yet:
nested_vmx_merge_pmu_msr_bitmaps(vmx, msr_bitmap_1, msr_bitmap_l0);
and handle the enable_mediated_pmu check in the helper.
> +
> kvm_vcpu_unmap(vcpu, &vmx->nested.msr_bitmap_map, false);
>
> vmx->nested.force_msr_bitmap_recalc = false;
> --
> 2.46.0.rc1.232.g9752f9e123-goog
>
