Re: [Xen-devel] [PATCH RFC V4 4/5] kvm : pv-ticketlocks support for linux guests running on KVM hypervisor

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 01/19/2012 12:54 AM, Srivatsa Vaddagiri wrote:
>
>> That logic relies on the "kick" being level triggered, so that "kick"
>> before "block" will cause the block to fall out immediately.  If you're
>> using "hlt" as the block and it has the usual edge-triggered behaviour,
>> what stops a "kick-before-hlt" from losing the kick?
> Hmm ..'hlt' should result in a check for kick request (in hypervisor
> context) before vcpu is put to sleep. IOW vcpu1 that is attempting to kick 
> vcpu0
> will set a 'somebody_tried_kicking_vcpu0' flag, which hypervisor should check 
> before it puts vcpu0 to sleep because of trapped 'hlt' instruction.
>
> Won't that trap the 'kick-before-hlt' case? What am I missing here?

Nothing, that sounds fine.  It wasn't clear to me that your kick
operation left persistent state, and so has a level-triggered effect on hlt.

    J

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