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authorVitaly Kuznetsov <vkuznets@redhat.com>2024-09-17 18:00:50 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2024-10-17 12:30:21 +0200
commitd3177e2e4353824a650434c57471615d43507500 (patch)
tree017ae69967cbddb9ef38c4213d343bf05d6059b3
parent7d7b9c7655a26e09c800ef40373078a80e90d9f3 (diff)
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target/i386: Make sure SynIC state is really updated before KVM_RUN
'hyperv_synic' test from KVM unittests was observed to be flaky on certain hardware (hangs sometimes). Debugging shows that the problem happens in hyperv_sint_route_new() when the test tries to set up a new SynIC route. The function bails out on: if (!synic->sctl_enabled) { goto cleanup; } but the test writes to HV_X64_MSR_SCONTROL just before it starts establishing SINT routes. Further investigation shows that synic_update() (called from async_synic_update()) happens after the SINT setup attempt and not before. Apparently, the comment before async_safe_run_on_cpu() in kvm_hv_handle_exit() does not correctly describe the guarantees async_safe_run_on_cpu() gives. In particular, async worked added to a CPU is actually processed from qemu_wait_io_event() which is not always called before KVM_RUN, i.e. kvm_cpu_exec() checks whether an exit request is pending for a CPU and if not, keeps running the vCPU until it meets an exit it can't handle internally. Hyper-V specific MSR writes are not automatically trigger an exit. Fix the issue by simply raising an exit request for the vCPU where SynIC update was queued. This is not a performance critical path as SynIC state does not get updated so often (and async_safe_run_on_cpu() is a big hammer anyways). Reported-by: Jan Richter <jarichte@redhat.com> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Link: https://lore.kernel.org/r/20240917160051.2637594-4-vkuznets@redhat.com Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--target/i386/kvm/hyperv.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/target/i386/kvm/hyperv.c b/target/i386/kvm/hyperv.c
index b94f12a..70b89ca 100644
--- a/target/i386/kvm/hyperv.c
+++ b/target/i386/kvm/hyperv.c
@@ -80,6 +80,7 @@ int kvm_hv_handle_exit(X86CPU *cpu, struct kvm_hyperv_exit *exit)
* necessary because memory hierarchy is being changed
*/
async_safe_run_on_cpu(CPU(cpu), async_synic_update, RUN_ON_CPU_NULL);
+ cpu_exit(CPU(cpu));
return EXCP_INTERRUPT;
case KVM_EXIT_HYPERV_HCALL: {