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List:       kvm
Subject:    [PATCH 4/6] KVM: x86: Fix determining flat mode in recalculate_apic_map
From:       Nadav Amit <namit () cs ! technion ! ac ! il>
Date:       2014-09-30 17:49:17
Message-ID: 1412099359-5316-5-git-send-email-namit () cs ! technion ! ac ! il
[Download RAW message or body]

Determining flat mode according to cid_mask is wrong, since currently KVM
supports zero clusters in x2apic mode. Use ldr_bits instead.

Since we recalculate the apic map whenever the DFR is changed, the bug appears
to have no effect, and perhaps the entire check can be removed.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
 arch/x86/kvm/lapic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index b8345dd..cfce429 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -171,7 +171,7 @@ static void recalculate_apic_map(struct kvm *kvm)
 			new->cid_mask = (1 << KVM_X2APIC_CID_BITS) - 1;
 			new->lid_mask = 0xffff;
 		} else if (kvm_apic_sw_enabled(apic) &&
-				!new->cid_mask /* flat mode */ &&
+				new->ldr_bits == 8 /* flat mode */ &&
 				kvm_apic_get_reg(apic, APIC_DFR) == APIC_DFR_CLUSTER) {
 			new->cid_shift = 4;
 			new->cid_mask = 0xf;
-- 
1.9.1

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