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KVM: PPC: Book3S HV: Don't try to signal cpu -1

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If the target vcpu for kvmppc_fast_vcpu_kick_hv() is not running on
any CPU, then we will have vcpu->arch.thread_cpu == -1, and as it
happens, kvmppc_fast_vcpu_kick_hv will call kvmppc_ipi_thread with
-1 as the cpu argument.  Although this is not meaningful, in the past,
before commit 1704a81cce ("KVM: PPC: Book3S HV: Use msgsnd for IPIs
to other cores on POWER9", 2016-11-18), it was harmless because CPU
-1 is not in the same core as any real CPU thread.  On a POWER9,
however, we don't do the "same core" check, so we were trying to
do a msgsnd to thread -1, which is invalid.  To avoid this, we add
a check to see that vcpu->arch.thread_cpu is >= 0 before calling
kvmppc_ipi_thread() with it.  Since vcpu->arch.thread_vcpu can change
asynchronously, we use READ_ONCE to ensure that the value we check is
the same value that we use as the argument to kvmppc_ipi_thread().

Fixes: 1704a81cce ("KVM: PPC: Book3S HV: Use msgsnd for IPIs to other cores on POWER9")
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras 2016-12-20 14:02:29 +11:00
parent a17f32270a
commit 3deda5e50c
1 changed files with 2 additions and 1 deletions
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3
arch/powerpc/kvm/book3s_hv.c
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@ -182,7 +182,8 @@ static void kvmppc_fast_vcpu_kick_hv(struct kvm_vcpu *vcpu)
++vcpu->stat.halt_wakeup;
}
if (kvmppc_ipi_thread(vcpu->arch.thread_cpu))
cpu = READ_ONCE(vcpu->arch.thread_cpu);
if (cpu >= 0 && kvmppc_ipi_thread(cpu))
return;
/* CPU points to the first thread of the core */