On 20/10/17 11:10, Paul Durrant wrote:
-----Original Message-----
From: Julien Grall [mailto:[email protected]]
Sent: 20 October 2017 11:00
To: Paul Durrant <[email protected]>; 'Jan Beulich'
<[email protected]>
Cc: Julien Grall <[email protected]>; Andrew Cooper
<[email protected]>; George Dunlap
<[email protected]>; Ian Jackson <[email protected]>; Roger
Pau Monne <[email protected]>; Wei Liu <[email protected]>; Stefano
Stabellini <[email protected]>; [email protected]; Konrad
Rzeszutek Wilk <[email protected]>; Daniel De Graaf
<[email protected]>; Tim (Xen.org) <[email protected]>
Subject: Re: [Xen-devel] [PATCH v12 05/11] x86/mm: add
HYPERVISOR_memory_op to acquire guest resources
Hi Paul,
On 20/10/17 09:26, Paul Durrant wrote:
-----Original Message-----
From: Jan Beulich [mailto:[email protected]]
Sent: 20 October 2017 07:25
To: Julien Grall <[email protected]>
Cc: Julien Grall <[email protected]>; Andrew Cooper
<[email protected]>; George Dunlap
<[email protected]>; Ian Jackson <[email protected]>; Paul
Durrant <[email protected]>; Roger Pau Monne
<[email protected]>; Wei Liu <[email protected]>; Stefano Stabellini
<[email protected]>; [email protected]; Konrad
Rzeszutek
Wilk <[email protected]>; Daniel De Graaf
<[email protected]>;
Tim (Xen.org) <[email protected]>
Subject: Re: [Xen-devel] [PATCH v12 05/11] x86/mm: add
HYPERVISOR_memory_op to acquire guest resources
On 19.10.17 at 18:21, <[email protected]> wrote:
Looking a bit more at the resource you can acquire from this hypercall.
Some of them are allocated using alloc_xenheap_page() so not assigned
to
a domain.
So I am not sure how you can expect a function set_foreign_p2m_entry
to
take reference in that case.
Hmm, with the domain parameter added, DOMID_XEN there (for
Xen heap pages) could identify no references to be taken, if that
was really the intended behavior in that case. However, even for
Xen heap pages life time tracking ought to be done - it is for a
reason that share_xen_page_with_guest() assigns the target
domain as the owner of such pages, as that allows get_page() to
succeed for them.
Hi Julien,
So, nothing I'm doing here is making anything worse, right? Grant tables are
assigned to the guest, and IOREQ server pages are allocated with
alloc_domheap_page() so nothing is anonymous.
I don't think grant tables is assigned to the guest today. They are
allocated using xenheap_pages() and I can't find
share_xen_page_with_guest().
The guest would not be able to map them if they were not assigned in some way!
Do you mean for PV? For HVM/PVH, we don't check whether the page is
assigned (see gnttab_map_frame).
See the code block at
http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/common/grant_table.c;hb=HEAD#l1716
It calls gnttab_create_shared_page() which is what calls through to
share_xen_page_with_guest().
Thank you for the link, I will have a look.
Anyway, I discussed with Stefano about it. set_foreign_p2m_entry is
going to be left unimplemented on Arm until someone as time to implement
correctly the function.
That makes sense. Do you still have any issues with this patch apart from the
cosmetic ones you spotted in the header?
No. Although, may I request to add a comment in the ARM helpers about
the reference counting?
Cheers,
--
Julien Grall
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