Re: obtain a list of granttable PFNs from toolstack

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.04.2021 12:17, Olaf Hering wrote:
> Am Wed, 28 Apr 2021 11:49:59 +0200
> schrieb Jan Beulich <jbeulich@xxxxxxxx>:
>> On 28.04.2021 09:50, Olaf Hering wrote:
>>> Is there an API to get a list of PFNs which are currently being active in 
>>> the grant table for a given domid?  
>> 
>> Also, what do you mean by "active in the grant table"?
> 
> I'm not familiar with grants. My guess is, a domU pro-actively shares some of 
> its pages with someone else. These shared pages have to be tracked somewhere, 
> and I guess Xen has to establish proper access permissions for such pages. I 
> guess the "grant table" is the place where things are collected.

The grant table is where the guest stores which pages it allows to
be accessed by which other domains. Upon request to access a grant,
Xen then updates that table entry to indicate what access is
currently in progress.

> Looking through xen/grant_table.h, I see no API. But that might be the wrong 
> place anyway.

There's none, and so far I can't see a reason why one would be
wanted / needed. Any inspection results are immediately stale
afterwards, as there's no synchronization at all to what guests
may put when into their grant table.

It might help if you would outline what you're actually after by
knowing a domain's active grants.

Jan