Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

From: Yang Zhang
Date: Thu Jan 21 2016 - 23:00:31 EST

On 2016/1/22 1:21, rkrcmar@xxxxxxxxxx wrote:
2016-01-21 05:33+0000, Wu, Feng:
From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
owner@xxxxxxxxxxxxxxx] On Behalf Of Yang Zhang
On 2016/1/20 9:42, Feng Wu wrote:
+ /*
+ * We may find a hardware disabled LAPIC here, if
+ * is the case, print out a error message once for each
+ * guest and return.
+ */
+ if (!dst[idx-1] &&
+ (kvm->arch.disabled_lapic_found == 0)) {
+ kvm->arch.disabled_lapic_found = 1;
+ printk(KERN_ERR
+ "Disabled LAPIC found during irq
+ goto out;

What does "goto out" mean? Inject successfully or fail? According the
value of ret which is set to ture here, it means inject successfully but

(true actually means that fast path did the job and slow path isn't

i = -1.

(I think there isn't a practical difference between *r=-1 and *r=0.)

Currently, if *r == -1, the remote_irr may get set. But it seems wrong. I need to have a double check to see whether it is a bug in current code.

Oh, I didn't notice 'ret' is initialized to true, I thought it was initialized
to false like another function, I should add a "ret = false' here. We should
failed to inject the interrupt since hardware disabled LAPIC is found.

'ret = true' is the better one. We know that the interrupt is not
deliverable [1], so there's no point in trying to deliver with the slow
path. We behave similarly when the interrupt targets a single disabled

1: Well ... it's possible that slowpath would deliver it thanks to
different handling of disabled APICs, but it's undefined behavior,

why it is undefined behavior? Besides, why we will keep two different handling logic for the fast path and slow path? It looks weird.

so it doesn't matter matter if we don't try.

best regards