When the host initiates a wrmsr through KVM_SET_MSRS don't print an
error if the PMU is disabled, doing so can cause a noticeable stall
while printing the error message.
The profile below was taken while calling KVM_SET_MSRS on the pmu
counters while the PMU was disabled in KVM. Even though the print is
rate limited it still manages to consume by far the majority of the
time.
- 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
A stall in this situation could have an impact on live migration. So,
to avoid that disable the print if the write is initiated by the host.
Fixes: 5753785fa977 ("KVM: do not #GP on perf MSR writes when vPMU is disabled")
Signed-off-by: Aaron Lewis <aaronlewis@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9cf1ba865562..a3b842467bd2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3778,7 +3778,7 @@ 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;
+ pr = !msr_info->host_initiated;
fallthrough;
case MSR_K7_EVNTSEL0 ... MSR_K7_EVNTSEL3:
case MSR_P6_EVNTSEL0 ... MSR_P6_EVNTSEL1:
--
2.38.1.273.g43a17bfeac-goog
