Patch "KVM: PPC: Book3S HV: Don't try to signal cpu -1" has been added to the 4.10-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     kvm-ppc-book3s-hv-don-t-try-to-signal-cpu-1.patch

and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Mackerras <[email protected]>
Date: Tue, 20 Dec 2016 14:02:29 +1100
Subject: KVM: PPC: Book3S HV: Don't try to signal cpu -1

From: Paul Mackerras <[email protected]>

commit 3deda5e50c893be38c1b6b3a73f8f8fb5560baa4 upstream.

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().

---
 arch/powerpc/kvm/book3s_hv.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -182,7 +182,8 @@ static void kvmppc_fast_vcpu_kick_hv(str
 		++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 */

Patches currently in stable-queue which might be from [email protected] are

queue-4.10/powerpc-mm-fixup-wrong-lpcr_vrmasd-value.patch queue-4.10/kvm-ppc-book3s-hv-don-t-try-to-signal-cpu-1.patch