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authorVitaly Kuznetsov <vkuznets@redhat.com>2019-03-13 20:13:42 +0300
committerPaolo Bonzini <pbonzini@redhat.com>2019-03-28 19:29:03 +0300
commit013cc6ebbf41496ce4badedd71ea6d4a6d198c14 (patch)
treeaa9ed54a4dee5bf122e1429c25f0115235c14b8c /arch
parent2bdb76c015df7125783d8394d6339d181cb5bc30 (diff)
downloadlinux-013cc6ebbf41496ce4badedd71ea6d4a6d198c14.tar.xz
x86/kvm/hyper-v: avoid spurious pending stimer on vCPU init
When userspace initializes guest vCPUs it may want to zero all supported MSRs including Hyper-V related ones including HV_X64_MSR_STIMERn_CONFIG/ HV_X64_MSR_STIMERn_COUNT. With commit f3b138c5d89a ("kvm/x86: Update SynIC timers on guest entry only") we began doing stimer_mark_pending() unconditionally on every config change. The issue I'm observing manifests itself as following: - Qemu writes 0 to STIMERn_{CONFIG,COUNT} MSRs and marks all stimers as pending in stimer_pending_bitmap, arms KVM_REQ_HV_STIMER; - kvm_hv_has_stimer_pending() starts returning true; - kvm_vcpu_has_events() starts returning true; - kvm_arch_vcpu_runnable() starts returning true; - when kvm_arch_vcpu_ioctl_run() gets into (vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED) case: - kvm_vcpu_block() gets in 'kvm_vcpu_check_block(vcpu) < 0' and returns immediately, avoiding normal wait path; - -EAGAIN is returned from kvm_arch_vcpu_ioctl_run() immediately forcing userspace to retry. So instead of normal wait path we get a busy loop on all secondary vCPUs before they get INIT signal. This seems to be undesirable, especially given that this happens even when Hyper-V extensions are not used. Generally, it seems to be pointless to mark an stimer as pending in stimer_pending_bitmap and arm KVM_REQ_HV_STIMER as the only thing kvm_hv_process_stimers() will do is clear the corresponding bit. We may just not mark disabled timers as pending instead. Fixes: f3b138c5d89a ("kvm/x86: Update SynIC timers on guest entry only") Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/hyperv.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 27c43525a05f..421899f6ad7b 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -526,7 +526,9 @@ static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config,
new_config.enable = 0;
stimer->config.as_uint64 = new_config.as_uint64;
- stimer_mark_pending(stimer, false);
+ if (stimer->config.enable)
+ stimer_mark_pending(stimer, false);
+
return 0;
}
@@ -542,7 +544,10 @@ static int stimer_set_count(struct kvm_vcpu_hv_stimer *stimer, u64 count,
stimer->config.enable = 0;
else if (stimer->config.auto_enable)
stimer->config.enable = 1;
- stimer_mark_pending(stimer, false);
+
+ if (stimer->config.enable)
+ stimer_mark_pending(stimer, false);
+
return 0;
}