Re: Intermittent guest kernel crashes with v4.5-rc6.

[Shanker Donthineni <shankerd@codeaurora.org>]

On 03/02/2016 11:35 AM, Marc Zyngier wrote:
> On 02/03/16 15:48, Shanker Donthineni wrote:
>
>> We haven't started running heavy workloads in VMs. So far we
>> have noticed this random nature behavior only during guest
>> kernel boot (at EL1).  
>>
>> We didn't see this problem on 4.3 kernel. Do you think it is
>> related to TLB conflicts?
> I cannot imagine why a DSB would solve a TLB conflict. But the fact that
> you didn't see it crashing on 4.3 is a good indication that something
> else it at play.
>
> In 4.5, we've rewritten a large part of KVM in C, which has changed the
> ordering of the various accesses a lot. It could be that a latent
> problem is now exposed more widely.
>
> Can you try moving this DSB around and find out what is the earliest
> point where it solves this problem? Some sort of bisection?
The maximum I can move up 'dsb ishst' to the beginning of
__guest_enter() but not out side of this function.

I don't understand why it is failing below code, branch
instruction causing problems.

    /* Jump in the fire! */
+  dsb(ishst);
    exit_code = __guest_enter(vcpu, host_ctxt);
    /* And we're baaack! */

> Thanks,
>
> 	M.

-- 
Shanker Donthineni
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project