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KVM: x86/pmu: Gate all "unimplemented MSR" prints on report_ignored_msrs
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Add helpers to print unimplemented MSR accesses and condition all such
prints on report_ignored_msrs, i.e. honor userspace's request to not
print unimplemented MSRs.  Even though vcpu_unimpl() is ratelimited,
printing can still be problematic, e.g. if a print gets stalled when host
userspace is writing MSRs during live migration, an effective stall can
result in very noticeable disruption in the guest.

E.g. the profile below was taken while calling KVM_SET_MSRS on the PMU
counters while the PMU was disabled in KVM.

  -   99.75%     0.00%  [.] __ioctl
   - __ioctl
      - 99.74% entry_SYSCALL_64_after_hwframe
           do_syscall_64
           sys_ioctl
         - do_vfs_ioctl
            - 92.48% kvm_vcpu_ioctl
               - kvm_arch_vcpu_ioctl
                  - 85.12% kvm_set_msr_ignored_check
                       svm_set_msr
                       kvm_set_msr_common
                       printk
                       vprintk_func
                       vprintk_default
                       vprintk_emit
                       console_unlock
                       call_console_drivers
                       univ8250_console_write
                       serial8250_console_write
                       uart_console_write

Reported-by: Aaron Lewis <aaronlewis@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20230124234905.3774678-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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@sean-jc
sean-jc committed Jan 27, 2023
1 parent 8911ce6 commit e76ae52
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Showing 5 changed files with 24 additions and 25 deletions.
10 changes: 4 additions & 6 deletions arch/x86/kvm/hyperv.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1430,8 +1430,7 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
return syndbg_set_msr(vcpu, msr, data, host);
default:
vcpu_unimpl(vcpu, "Hyper-V unhandled wrmsr: 0x%x data 0x%llx\n",
msr, data);
kvm_pr_unimpl_wrmsr(vcpu, msr, data);
return 1;
}
return 0;
Expand Down Expand Up @@ -1552,8 +1551,7 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
return 1;
break;
default:
vcpu_unimpl(vcpu, "Hyper-V unhandled wrmsr: 0x%x data 0x%llx\n",
msr, data);
kvm_pr_unimpl_wrmsr(vcpu, msr, data);
return 1;
}

Expand Down Expand Up @@ -1608,7 +1606,7 @@ static int kvm_hv_get_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
return syndbg_get_msr(vcpu, msr, pdata, host);
default:
vcpu_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);
kvm_pr_unimpl_rdmsr(vcpu, msr);
return 1;
}

Expand Down Expand Up @@ -1673,7 +1671,7 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
data = APIC_BUS_FREQUENCY;
break;
default:
vcpu_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);
kvm_pr_unimpl_rdmsr(vcpu, msr);
return 1;
}
*pdata = data;
Expand Down
5 changes: 2 additions & 3 deletions arch/x86/kvm/svm/svm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3015,8 +3015,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
break;
case MSR_IA32_DEBUGCTLMSR:
if (!lbrv) {
vcpu_unimpl(vcpu, "%s: MSR_IA32_DEBUGCTL 0x%llx, nop\n",
__func__, data);
kvm_pr_unimpl_wrmsr(vcpu, ecx, data);
break;
}
if (data & DEBUGCTL_RESERVED_BITS)
Expand Down Expand Up @@ -3045,7 +3044,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
case MSR_VM_CR:
return svm_set_vm_cr(vcpu, data);
case MSR_VM_IGNNE:
vcpu_unimpl(vcpu, "unimplemented wrmsr: 0x%x data 0x%llx\n", ecx, data);
kvm_pr_unimpl_wrmsr(vcpu, ecx, data);
break;
case MSR_AMD64_DE_CFG: {
struct kvm_msr_entry msr_entry;
Expand Down
4 changes: 1 addition & 3 deletions arch/x86/kvm/vmx/vmx.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2206,9 +2206,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

invalid = data & ~vmx_get_supported_debugctl(vcpu, msr_info->host_initiated);
if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) {
if (report_ignored_msrs)
vcpu_unimpl(vcpu, "%s: BTF|LBR in IA32_DEBUGCTLMSR 0x%llx, nop\n",
__func__, data);
kvm_pr_unimpl_wrmsr(vcpu, msr_index, data);
data &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
invalid &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
}
Expand Down
18 changes: 5 additions & 13 deletions arch/x86/kvm/x86.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3560,7 +3560,6 @@ static void record_steal_time(struct kvm_vcpu *vcpu)

int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
{
bool pr = false;
u32 msr = msr_info->index;
u64 data = msr_info->data;

Expand Down Expand Up @@ -3606,15 +3605,13 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (data == BIT_ULL(18)) {
vcpu->arch.msr_hwcr = data;
} else if (data != 0) {
vcpu_unimpl(vcpu, "unimplemented HWCR wrmsr: 0x%llx\n",
data);
kvm_pr_unimpl_wrmsr(vcpu, msr, data);
return 1;
}
break;
case MSR_FAM10H_MMIO_CONF_BASE:
if (data != 0) {
vcpu_unimpl(vcpu, "unimplemented MMIO_CONF_BASE wrmsr: "
"0x%llx\n", data);
kvm_pr_unimpl_wrmsr(vcpu, msr, data);
return 1;
}
break;
Expand Down Expand Up @@ -3794,16 +3791,13 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

case MSR_K7_PERFCTR0 ... MSR_K7_PERFCTR3:
case MSR_P6_PERFCTR0 ... MSR_P6_PERFCTR1:
pr = true;
fallthrough;
case MSR_K7_EVNTSEL0 ... MSR_K7_EVNTSEL3:
case MSR_P6_EVNTSEL0 ... MSR_P6_EVNTSEL1:
if (kvm_pmu_is_valid_msr(vcpu, msr))
return kvm_pmu_set_msr(vcpu, msr_info);

if (pr || data != 0)
vcpu_unimpl(vcpu, "disabled perfctr wrmsr: "
"0x%x data 0x%llx\n", msr, data);
if (data)
kvm_pr_unimpl_wrmsr(vcpu, msr, data);
break;
case MSR_K7_CLK_CTL:
/*
Expand Down Expand Up @@ -3831,9 +3825,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
/* Drop writes to this legacy MSR -- see rdmsr
* counterpart for further detail.
*/
if (report_ignored_msrs)
vcpu_unimpl(vcpu, "ignored wrmsr: 0x%x data 0x%llx\n",
msr, data);
kvm_pr_unimpl_wrmsr(vcpu, msr, data);
break;
case MSR_AMD64_OSVW_ID_LENGTH:
if (!guest_cpuid_has(vcpu, X86_FEATURE_OSVW))
Expand Down
12 changes: 12 additions & 0 deletions arch/x86/kvm/x86.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -331,6 +331,18 @@ extern bool report_ignored_msrs;

extern bool eager_page_split;

static inline void kvm_pr_unimpl_wrmsr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
{
if (report_ignored_msrs)
vcpu_unimpl(vcpu, "Unhandled WRMSR(0x%x) = 0x%llx\n", msr, data);
}

static inline void kvm_pr_unimpl_rdmsr(struct kvm_vcpu *vcpu, u32 msr)
{
if (report_ignored_msrs)
vcpu_unimpl(vcpu, "Unhandled RDMSR(0x%x)\n", msr);
}

static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
{
return pvclock_scale_delta(nsec, vcpu->arch.virtual_tsc_mult,
Expand Down

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