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author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2024-09-17 18:00:50 +0200 |
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committer | Paolo Bonzini <pbonzini@redhat.com> | 2024-10-17 12:30:21 +0200 |
commit | d3177e2e4353824a650434c57471615d43507500 (patch) | |
tree | 017ae69967cbddb9ef38c4213d343bf05d6059b3 | |
parent | 7d7b9c7655a26e09c800ef40373078a80e90d9f3 (diff) | |
download | qemu-d3177e2e4353824a650434c57471615d43507500.zip qemu-d3177e2e4353824a650434c57471615d43507500.tar.gz qemu-d3177e2e4353824a650434c57471615d43507500.tar.bz2 |
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.c | 1 |
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: { |