linux-kernel - [PATCH v6 1/2] KVM: remove NULL return path for vcpu ids >= KVM_MAX

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Date:	Mon, 09 May 2016 18:11:54 +0200
From:	Greg Kurz <gkurz@...ux.vnet.ibm.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, james.hogan@...tec.com,
	mingo@...hat.com
Cc:	linux-mips@...ux-mips.org, kvm@...r.kernel.org, rkrcmar@...hat.com,
	linux-kernel@...r.kernel.org,
	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	qemu-ppc@...gnu.org, Cornelia Huck <cornelia.huck@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>,
	David Gibson <david@...son.dropbear.id.au>
Subject: [PATCH v6 1/2] KVM: remove NULL return path for vcpu ids >=
 KVM_MAX_VCPUS

Commit c896939f7cff ("KVM: use heuristic for fast VCPU lookup by id") added
a return path that prevents vcpu ids to exceed KVM_MAX_VCPUS. This is a
problem for powerpc where vcpu ids can grow up to 8*KVM_MAX_VCPUS.

This patch simply reverses the logic so that we only try fast path if the
vcpu id can be tried as an index in kvm->vcpus[]. The slow path is not
affected by the change.

Reviewed-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@...ibm.com>
Signed-off-by: Greg Kurz <gkurz@...ux.vnet.ibm.com>
---
 include/linux/kvm_host.h |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5276fe0916fc..23bfe1bd159c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -447,12 +447,13 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)
 
 static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
 {
-	struct kvm_vcpu *vcpu;
+	struct kvm_vcpu *vcpu = NULL;
 	int i;
 
-	if (id < 0 || id >= KVM_MAX_VCPUS)
+	if (id < 0)
 		return NULL;
-	vcpu = kvm_get_vcpu(kvm, id);
+	if (id < KVM_MAX_VCPUS)
+		vcpu = kvm_get_vcpu(kvm, id);
 	if (vcpu && vcpu->vcpu_id == id)
 		return vcpu;
 	kvm_for_each_vcpu(i, vcpu, kvm)