65 lines
2.7 KiB
Diff
65 lines
2.7 KiB
Diff
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From 327e8c65d28dc357c02b508e6485e7c57d4d1efa Mon Sep 17 00:00:00 2001
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From: Vitaly Kuznetsov <vkuznets@redhat.com>
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Date: Tue, 7 Jan 2025 13:43:32 +0100
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Subject: [PATCH 1/4] target/i386: Make sure SynIC state is really updated
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before KVM_RUN
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RH-Author: Vitaly Kuznetsov <vkuznets@redhat.com>
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RH-MergeRequest: 314: target/i386: Make sure SynIC state is really updated before KVM_RUN
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RH-Jira: RHEL-73002
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Maxim Levitsky <None>
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RH-Commit: [1/1] 2d8f7605e3efd3c76d16a2cb9e7c0898786fb4e9 (vkuznets/qemu-kvm)
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'hyperv_synic' test from KVM unittests was observed to be flaky on certain
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hardware (hangs sometimes). Debugging shows that the problem happens in
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hyperv_sint_route_new() when the test tries to set up a new SynIC
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route. The function bails out on:
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if (!synic->sctl_enabled) {
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goto cleanup;
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}
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but the test writes to HV_X64_MSR_SCONTROL just before it starts
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establishing SINT routes. Further investigation shows that
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synic_update() (called from async_synic_update()) happens after the SINT
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setup attempt and not before. Apparently, the comment before
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async_safe_run_on_cpu() in kvm_hv_handle_exit() does not correctly describe
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the guarantees async_safe_run_on_cpu() gives. In particular, async worked
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added to a CPU is actually processed from qemu_wait_io_event() which is not
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always called before KVM_RUN, i.e. kvm_cpu_exec() checks whether an exit
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request is pending for a CPU and if not, keeps running the vCPU until it
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meets an exit it can't handle internally. Hyper-V specific MSR writes are
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not automatically trigger an exit.
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Fix the issue by simply raising an exit request for the vCPU where SynIC
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update was queued. This is not a performance critical path as SynIC state
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does not get updated so often (and async_safe_run_on_cpu() is a big hammer
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anyways).
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Reported-by: Jan Richter <jarichte@redhat.com>
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Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
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Link: https://lore.kernel.org/r/20240917160051.2637594-4-vkuznets@redhat.com
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit d3177e2e4353824a650434c57471615d43507500)
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Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
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---
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target/i386/kvm/hyperv.c | 1 +
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1 file changed, 1 insertion(+)
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diff --git a/target/i386/kvm/hyperv.c b/target/i386/kvm/hyperv.c
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index b94f12acc2..70b89cacf9 100644
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--- a/target/i386/kvm/hyperv.c
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+++ b/target/i386/kvm/hyperv.c
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@@ -80,6 +80,7 @@ int kvm_hv_handle_exit(X86CPU *cpu, struct kvm_hyperv_exit *exit)
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* necessary because memory hierarchy is being changed
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*/
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async_safe_run_on_cpu(CPU(cpu), async_synic_update, RUN_ON_CPU_NULL);
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+ cpu_exit(CPU(cpu));
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return EXCP_INTERRUPT;
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case KVM_EXIT_HYPERV_HCALL: {
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--
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2.39.3
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