Re: [Xen-devel] Re: how to handle paged hypercall args?

[Keir Fraser <keir@xxxxxxx>]

On 15/11/2010 10:20, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:

>> Yes, and you'd never turn on paging for dom0 itself. That would never work!
> 
> :) No, the issue is if dom0 (or whichever dom the pager lives in) is
> trying an operation on domU's memory that hits a paged-out page
> (e.g. qemu or similar is mapping it) with its only vpcu - you can't
> just block or spin.  You need to let dom0 schedule the pager process.
> 
>> Changing every user of the guest accessor macros to retry via guest space is
>> really not tenable. We'd never get all the bugs out.
> 
> Right now, I can't see another way of doing it.  Grants can be handled
> by shadowing the guest grant table and pinning granted frames so the
> block happens in domU (performance-- but you're already paging, right?)
> but what about qemu, xenctx, save/restore...?

We're talking about copy_to/from_guest, and friends, here. They always
implicitly act on the local domain, so the issue you raise is not a problem
there. Dom0 mappings of domU memory are a separate issue, presumably already
considered and dealt with to some extent, no doubt.

 -- Keir




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel