[PATCH] ARM: KVM: fix unbalanced get_cpu() in access_dcsw

[PATCH] ARM: KVM: fix unbalanced get_cpu() in access_dcsw

[Marc Zyngier]

In the very unlikely event where a guest would be foolish enough to
*read* from a write-only cache maintainance register, we end up
with preemption disabled, due to a misplaced get_cpu().

Just move the "is_write" test outside of the critical section.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kvm/coproc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c
index 94eee8b..8eea97b 100644
--- a/arch/arm/kvm/coproc.c
+++ b/arch/arm/kvm/coproc.c
@@ -79,11 +79,11 @@ static bool access_dcsw(struct kvm_vcpu *vcpu,
 	unsigned long val;
 	int cpu;
 
-	cpu = get_cpu();
-
 	if (!p->is_write)
 		return read_from_write_only(vcpu, p);
 
+	cpu = get_cpu();
+
 	cpumask_setall(&vcpu->arch.require_dcache_flush);
 	cpumask_clear_cpu(cpu, &vcpu->arch.require_dcache_flush);
 
-- 
1.8.1.4

[PATCH] ARM: KVM: fix unbalanced get_cpu() in access_dcsw

[Will Deacon]

On Fri, Apr 12, 2013 at 06:13:48PM +0100, Marc Zyngier wrote:
> In the very unlikely event where a guest would be foolish enough to
> *read* from a write-only cache maintainance register, we end up
> with preemption disabled, due to a misplaced get_cpu().
> 
> Just move the "is_write" test outside of the critical section.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

I found it second time around!

  Reported-by: Will Deacon <will.deacon@arm.com>

Will

[PATCH] ARM: KVM: fix unbalanced get_cpu() in access_dcsw

[Marc Zyngier]

On Fri, 12 Apr 2013 19:13:32 +0100, Will Deacon <will.deacon@arm.com>
wrote:
> On Fri, Apr 12, 2013 at 06:13:48PM +0100, Marc Zyngier wrote:
>> In the very unlikely event where a guest would be foolish enough to
>> *read* from a write-only cache maintainance register, we end up
>> with preemption disabled, due to a misplaced get_cpu().
>> 
>> Just move the "is_write" test outside of the critical section.
>> 
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> 
> I found it second time around!
> 
>   Reported-by: Will Deacon <will.deacon@arm.com>

Indeed you did! :-)

I'll add that to the commit, and on a couple of other as well...

        M.
-- 
Fast, cheap, reliable. Pick two.

[PATCH] ARM: KVM: fix unbalanced get_cpu() in access_dcsw

[Christoffer Dall]

On Fri, Apr 12, 2013 at 09:17:46PM +0200, Marc Zyngier wrote:
> On Fri, 12 Apr 2013 19:13:32 +0100, Will Deacon <will.deacon@arm.com>
> wrote:
> > On Fri, Apr 12, 2013 at 06:13:48PM +0100, Marc Zyngier wrote:
> >> In the very unlikely event where a guest would be foolish enough to
> >> *read* from a write-only cache maintainance register, we end up
> >> with preemption disabled, due to a misplaced get_cpu().
> >> 
> >> Just move the "is_write" test outside of the critical section.
> >> 
> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> > 
> > I found it second time around!
> > 
> >   Reported-by: Will Deacon <will.deacon@arm.com>
> 
> Indeed you did! :-)
> 
> I'll add that to the commit, and on a couple of other as well...

I applied the patch and added the tag, thanks.

-Christoffer

[PATCH] ARM: KVM: fix unbalanced get_cpu() in access_dcsw

[Christoffer Dall]

From: Marc Zyngier <marc.zyngier@arm.com>

In the very unlikely event where a guest would be foolish enough to
*read* from a write-only cache maintainance register, we end up
with preemption disabled, due to a misplaced get_cpu().

Just move the "is_write" test outside of the critical section.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
---
 arch/arm/kvm/coproc.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c
index 4ea9a98..7bed755 100644
--- a/arch/arm/kvm/coproc.c
+++ b/arch/arm/kvm/coproc.c
@@ -79,11 +79,11 @@ static bool access_dcsw(struct kvm_vcpu *vcpu,
 	u32 val;
 	int cpu;
 
-	cpu = get_cpu();
-
 	if (!p->is_write)
 		return read_from_write_only(vcpu, p);
 
+	cpu = get_cpu();
+
 	cpumask_setall(&vcpu->arch.require_dcache_flush);
 	cpumask_clear_cpu(cpu, &vcpu->arch.require_dcache_flush);
 
-- 
1.7.9.5