Re: [Xen-devel] [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 6/24/2016 2:12 PM, Jan Beulich wrote:
> > > > On 24.06.16 at 06:16, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > I'm now willing to take your suggestions:
> > a> still need the p2m resetting when ioreq server is unbounded;
> > b> disable log dirty feature if one ioreq server is bounded.
> >
> > Does anyone else has different opinions? Thanks!
> Hmm, in particular for a) I don't think I read that out of George's
> descriptions. But of course much depends on what you really
> mean by that: Do you want to say we need to guarantee all
> entries get reverted back, or do you instead mean to just kick
> off the conversion (via the misconfig mechanism)?
Thanks for your reply, Jan. I mean the misconfig mechanism.

> In any event, I think log-dirty shouldn't be disabled when an
> ioreq server binds the type, but as long as there are outstanding
> entries of that type. That way, the "cannot be migrated" state
> of a VM has a chance to clear.
Do you mean to disable log dirty by checking if there's outstanding 
p2m_ioreq_server
entries instead of the p2m->ioreq.server? How about we check both? 
Because only
checking the count of outstanding p2m_ioreq_server may prevent the live 
migration
when an ioreq server is unbound, but with p2m type not entirely synced.

> And then, thinking about it again especially in the context of
> the hvmctl series - the unbinding of the type is happening in a
> hypercall with built-in preemption capability. Hence there's not
> really an issue with how long that conversion may take, as
> long as there's no need to pause the guest for that time period.
> Which means you could first initiate conversion via the
> misconfig mechanism, but then immediately go ahead and walk
> the entire guest address space (or the relevant part of it, if
> the bounds got tracked) with continuations used as necessary.
Sorry, what's the misconfig mechanism good for if I still need to sweep 
the entire
p2m table immediately?

Thanks
Yu


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