Re: [Xen-devel] [V6 PATCH 6.2/7] pvh dom0: Add and remove foreign pages

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.12.13 at 03:34, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> On Tue, 17 Dec 2013 11:10:46 +0100
> Tim Deegan <tim@xxxxxxx> wrote:
> 
>> At 15:27 -0800 on 16 Dec (1387204042), Mukesh Rathor wrote:
>> > On Mon, 16 Dec 2013 08:40:41 +0000
>> > "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> > 
>> > > >>> On 14.12.13 at 03:48, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
>> > > >>> wrote:
>> > > >> Also, Jan may have an opinion about whether a teardown
>> > > >> operation that has to walk each p2m entry would have to be made
>> > > >> preemptible.  I'm not sure where we draw the line on such
>> > > >> things.
>> > > > 
>> > > > Since at present teardown cleanup of foreign is not really that
>> > > > important as its only applicable to dom0, let me submit another
>> > > > patch for it on Mon with few ideas. That would also keep this
>> > > > patch size reasonable, and keep you from having to look at the
>> > > > same code over and over. 
>> > > > 
>> > > > So, please take a look at the version below with above two
>> > > > fixes. If you approve it, i can resubmit the entire series
>> > > > rebased to latest with your ack on Monday, and the series can
>> > > > go in while we resolve the p2m teardown.
>> > > 
>> > > Going through the patch again, I'm not seeing any loop being
>> > > added. Am I missing something here?
>> > 
>> > Yes. Since the destruction of p2m leaking foreign pages only applies
>> > to control domain being destroyed, i don't think it is that critical
>> > that part get into 4.4.
>> 
>> Nak.  We can't let the tools break the refcounting.
> 
> BTW, it appears that currently this cleanup doesn't happen on PV. If on a 
> PV control domain and the tool stack has mapped foreign pages, and the 
> PV control domain dies, the refcnt will be messed up. Right?

I don't think so - the refcounts should all get properly dropped
as page tables get cleaned up.

Jan


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