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Subject[PATCH V5 2/2] kvm: ignore LBR and extra_reg
Date
From: Kan Liang <kan.liang@intel.com>

With -cpu host KVM reports LBR and extra_regs support, so the perf driver may accesses the LBR and extra_regs MSRs.
However, there is no LBR and extra_regs virtualization support yet. This could causes guest to crash.
As a workaround, KVM just simply ignore the LBR and extra_regs MSRs to lie the guest.

For reproducing the issue, please build the kernel with CONFIG_KVM_INTEL = y (for host kernel).
And CONFIG_PARAVIRT = n and CONFIG_KVM_GUEST = n (for guest kernel).
Start the guest with -cpu host.
Run perf record with --branch-any or --branch-filter in guest to trigger LBR #GP.
Run perf stat offcore events (E.g. LLC-loads/LLC-load-misses ...) in guest to trigger offcore_rsp #GP

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kan Liang <kan.liang@intel.com>

V3: add MSR_LBR_TOS
V4: add MSR_LBR_SELECT and MSR_PEBS_LD_LAT_THRESHOLD
V5: set_msr should return 0 to lie the guest
---
arch/x86/kvm/pmu.c | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index cbecaa9..5fd5b44 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -331,6 +331,18 @@ bool kvm_pmu_msr(struct kvm_vcpu *vcpu, u32 msr)
case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
ret = pmu->version > 1;
break;
+ case MSR_OFFCORE_RSP_0:
+ case MSR_OFFCORE_RSP_1:
+ case MSR_LBR_SELECT:
+ case MSR_PEBS_LD_LAT_THRESHOLD:
+ case MSR_LBR_TOS:
+ /* At most 8-deep LBR for core and atom */
+ case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 7:
+ case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 7:
+ /* 16-deep LBR for core i3/i5/i7 series processors */
+ case MSR_LBR_NHM_FROM ... MSR_LBR_NHM_FROM + 15:
+ case MSR_LBR_NHM_TO ... MSR_LBR_NHM_TO + 15:
+ return 1; /* to avoid crashes */
default:
ret = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)
|| get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0)
@@ -358,6 +370,19 @@ int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data)
case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
*data = pmu->global_ovf_ctrl;
return 0;
+ case MSR_OFFCORE_RSP_0:
+ case MSR_OFFCORE_RSP_1:
+ case MSR_LBR_SELECT:
+ case MSR_PEBS_LD_LAT_THRESHOLD:
+ case MSR_LBR_TOS:
+ /* At most 8-deep LBR for core and atom */
+ case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 7:
+ case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 7:
+ /* 16-deep LBR for core i3/i5/i7 series processors */
+ case MSR_LBR_NHM_FROM ... MSR_LBR_NHM_FROM + 15:
+ case MSR_LBR_NHM_TO ... MSR_LBR_NHM_TO + 15:
+ *data = 0;
+ return 0;
default:
if ((pmc = get_gp_pmc(pmu, index, MSR_IA32_PERFCTR0)) ||
(pmc = get_fixed_pmc(pmu, index))) {
@@ -409,6 +434,19 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 0;
}
break;
+ case MSR_OFFCORE_RSP_0:
+ case MSR_OFFCORE_RSP_1:
+ case MSR_LBR_SELECT:
+ case MSR_PEBS_LD_LAT_THRESHOLD:
+ case MSR_LBR_TOS:
+ /* At most 8-deep LBR for core and atom */
+ case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 7:
+ case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 7:
+ /* 16-deep LBR for core i3/i5/i7 series processors */
+ case MSR_LBR_NHM_FROM ... MSR_LBR_NHM_FROM + 15:
+ case MSR_LBR_NHM_TO ... MSR_LBR_NHM_TO + 15:
+ /* dummy for now */
+ return 0;
default:
if ((pmc = get_gp_pmc(pmu, index, MSR_IA32_PERFCTR0)) ||
(pmc = get_fixed_pmc(pmu, index))) {
--
1.8.3.1


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