linux-kernel - [PATCH 10/11] KVM: Fix local apic timer divide by zero

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Message-Id: <11929648921713-git-send-email-avi@qumranet.com>
Date:	Sun, 21 Oct 2007 13:08:11 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	kvm-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org,
	Kevin Pedretti <kevin.pedretti@...il.com>,
	Avi Kivity <avi@...ranet.com>
Subject: [PATCH 10/11] KVM: Fix local apic timer divide by zero

From: Kevin Pedretti <kevin.pedretti@...il.com>

kvm_lapic_reset() was initializing apic->timer.divide_count to 0,
which could potentially lead to a divide by zero error in
apic_get_tmcct().  Any guest that reads the APIC's CCR (current count)
register before setting DCR (divide configuration) would trigger a divide
by zero exception in the host kernel, leading to a host-OS crash.

This patch results in apic->timer.divide_count being initialized to
2 at reset, eliminating the bug (DCR=0 at reset, meaning divide by 2).

Signed-off-by: Kevin Pedretti <kevin.pedretti@...il.com>
Signed-off-by: Avi Kivity <avi@...ranet.com>
---
 drivers/kvm/lapic.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/kvm/lapic.c b/drivers/kvm/lapic.c
index a190587..443730e 100644
--- a/drivers/kvm/lapic.c
+++ b/drivers/kvm/lapic.c
@@ -853,7 +853,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu)
 		apic_set_reg(apic, APIC_ISR + 0x10 * i, 0);
 		apic_set_reg(apic, APIC_TMR + 0x10 * i, 0);
 	}
-	apic->timer.divide_count = 0;
+	update_divide_count(apic);
 	atomic_set(&apic->timer.pending, 0);
 	if (vcpu->vcpu_id == 0)
 		vcpu->apic_base |= MSR_IA32_APICBASE_BSP;
-- 
1.5.3

-
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