[PATCH] book3s_hv_rmhandlers:Pass the correct trap argument to kvmhv_commence_exit

[PATCH] book3s_hv_rmhandlers:Pass the correct trap argument to kvmhv_commence_exit

[Gautham R. Shenoy]

In guest_exit_cont we call kvmhv_commence_exit which expects the trap
number as the argument. However r3 doesn't contain the trap number at
this point and as a result we would be calling the function with a
spurious trap number.

Fix this by copying r12 into r3 before calling kvmhv_commence_exit as
r12 contains the trap number

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 4d70df2..f0d7c54 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -1170,6 +1170,7 @@ mc_cont:
 	bl	kvmhv_accumulate_time
 #endif
 
+	mr 	r3, r12
 	/* Increment exit count, poke other threads to exit */
 	bl	kvmhv_commence_exit
 	nop
-- 
1.9.3

Re: [PATCH] book3s_hv_rmhandlers:Pass the correct trap argument to kvmhv_commence_exit

[Sam Bobroff]

On Thu, May 21, 2015 at 01:57:04PM +0530, Gautham R. Shenoy wrote:
> In guest_exit_cont we call kvmhv_commence_exit which expects the trap
> number as the argument. However r3 doesn't contain the trap number at
> this point and as a result we would be calling the function with a
> spurious trap number.
> 
> Fix this by copying r12 into r3 before calling kvmhv_commence_exit as
> r12 contains the trap number
> 
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>

Hi Gautham,

I agree with your logic: r3 is quite clearly corrupted in that path. So:

Reviewed-by: Sam Bobroff <sam.bobroff@au1.ibm.com>

Just one comment: Do you have a case of this causing some visible problem due
to the corrupted trap number? (I'll test the patch if you do.)

Cheers,
Sam.

Re: [PATCH] book3s_hv_rmhandlers:Pass the correct trap argument to kvmhv_commence_exit

[Gautham R Shenoy]

Hi Sam,

On Fri, Aug 14, 2015 at 03:07:28PM +1000, Sam Bobroff wrote:
> On Thu, May 21, 2015 at 01:57:04PM +0530, Gautham R. Shenoy wrote:
> > In guest_exit_cont we call kvmhv_commence_exit which expects the trap
> > number as the argument. However r3 doesn't contain the trap number at
> > this point and as a result we would be calling the function with a
> > spurious trap number.
> > 
> > Fix this by copying r12 into r3 before calling kvmhv_commence_exit as
> > r12 contains the trap number
> > 
> > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> 
> Hi Gautham,
> 
> I agree with your logic: r3 is quite clearly corrupted in that path. So:
> 
> Reviewed-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
> 
> Just one comment: Do you have a case of this causing some visible problem due
> to the corrupted trap number? (I'll test the patch if you do.)
> 

Actually no! I found this bug while reviewing the code for some other issue.

> Cheers,
> Sam.

--
Thanks and Regards
gautham.