linux-kernel - [ 056/184] KVM: x86: relax MSR_KVM_SYSTEM

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Date:	Tue, 04 Jun 2013 19:22:26 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Marcelo Tosatti <mtosatti@...hat.com>, Willy Tarreau <w@....eu>
Subject: [ 056/184] KVM: x86: relax MSR_KVM_SYSTEM_TIME alignment check

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Marcelo Tosatti <mtosatti@...hat.com>

RHEL5 i386 guests register non 32-byte aligned addresses:

kvm-clock: cpu 1, msr 0:3018aa5, secondary cpu clock
kvm-clock: cpu 2, msr 0:301f8e9, secondary cpu clock
kvm-clock: cpu 3, msr 0:302672d, secondary cpu clock

Check for an address+len that would cross page boundary
instead.

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
[dannf: backported to Debian's 2.6.32]
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/x86/kvm/x86.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e24e9ce..79905f2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -925,9 +925,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 		/* ...but clean it before doing the actual write */
 		vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);
 
-		/* Check that the address is 32-byte aligned. */
-		if (vcpu->arch.time_offset &
-				(sizeof(struct pvclock_vcpu_time_info) - 1))
+		/* Check that address+len does not cross page boundary */
+		if ((vcpu->arch.time_offset + 
+			sizeof(struct pvclock_vcpu_time_info) - 1)
+			& PAGE_MASK)
 			break;
 
 		vcpu->arch.time_page =
-- 
1.7.12.2.21.g234cd45.dirty



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