From 3deda5e50c893be38c1b6b3a73f8f8fb5560baa4 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Tue, 20 Dec 2016 14:02:29 +1100 Subject: [PATCH] KVM: PPC: Book3S HV: Don't try to signal cpu -1 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 1704a81ccebc ("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: 1704a81ccebc ("KVM: PPC: Book3S HV: Use msgsnd for IPIs to other cores on POWER9") Signed-off-by: Paul Mackerras --- arch/powerpc/kvm/book3s_hv.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index ec34e39471a7..8d9cc07b1e9c 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -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 */