[ZESTY] [PATCH 27/33] KVM: PPC: Book3S HV: Don't try to signal cpu -1

Breno Leitao leitao at debian.org
Tue Mar 28 16:54:39 UTC 2017

From: Paul Mackerras <paulus at ozlabs.org>

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1675806

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 <paulus at ozlabs.org>
(cherry picked from commit 3deda5e50c893be38c1b6b3a73f8f8fb5560baa4)
Signed-off-by: Breno Leitao <breno.leitao at gmail.com>
 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 80076f34cbd8..bdf281cc88c0 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)
-	if (kvmppc_ipi_thread(vcpu->arch.thread_cpu))
+	cpu = READ_ONCE(vcpu->arch.thread_cpu);
+	if (cpu >= 0 && kvmppc_ipi_thread(cpu))
 	/* CPU points to the first thread of the core */

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