Re: [PATCH 2/2 v2] KVM: PPC: booke: Add watchdog emulation

[Scott Wood <scottwood@freescale.com>]

On 07/17/2012 11:51 AM, Alexander Graf wrote:
> On 07/17/2012 06:27 PM, Scott Wood wrote:
>> Determining whether we're on final expiration is based only on the
>> previous value of TSR[ENW,WIS] when the timer expires.  We look at TCR
>> to determine whether we need to actually exit to QEMU (as opposed to a
>> final expiration with no action, which still should result in the timer
>> being stopped), but I don't see any problematic races there as long as
>> we don't try to update TCR from that context.
> 
> Yeah, what I was trying to say is that I would like to keep the TSR
> state unmodified for the final expiry case. If user space decides to not
> act upon it, it should be able to call into VCPU_RUN and have the same
> behavior as if the watchdog never expired.

I agree, it would be racy for QEMU to have to clear TSR if it's not
doing a full reset.  And that fact is making me wonder if I should have
listened to you and kept TSR owned by the vcpu thread. :-)

-Scott