Hi Paul,
On 09/26/2018 01:01 PM, Paul Durrant wrote:
-----Original Message-----
From: Jan Beulich [mailto:jbeul...@suse.com]
Sent: 26 September 2018 12:57
To: Paul Durrant <paul.durr...@citrix.com>
Cc: Julien Grall <julien.gr...@arm.com>; Andrew Cooper
<andrew.coop...@citrix.com>; Roger Pau Monne <roger....@citrix.com>;
Stefano Stabellini <sstabell...@kernel.org>; xen-devel <xen-
de...@lists.xenproject.org>
Subject: RE: IOREQ server on Arm
On 26.09.18 at 13:02, <paul.durr...@citrix.com> wrote:
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1105,8 +1105,11 @@ static int acquire_resource(
for ( i = 0; !rc && i < xmar.nr_frames; i++ )
{
- rc = set_foreign_p2m_entry(currd, gfn_list[i],
- _mfn(mfn_list[i]));
+ rc = (xmar.flags & XENMEM_rsrc_acq_caller_owned) ?
+ guest_physmap_add_entry(currd, gfn_list[i],
+ _mfn(mfn_list[i]), 0,
p2m_ram_rw) :
+ set_foreign_p2m_entry(currd, gfn_list[i],
+ _mfn(mfn_list[i]));
/* rc should be -EIO for any iteration other than the first
*/
if ( rc && i )
rc = -EIO;
But the guest_physmap_add_entry() is problematic as it will IOMMU map
pages
as well, which is probably not wanted.
Yeah, I'd prefer if we avoided establishing IOMMU mappings here.
How about transforming set_foreign_p2m_entry() into
set_special_p2m_entry(), with a type passed in?
That sounds like it might work.
Julien, do you want page types to distinguish caller-owned resources from
normal RAM are you ok with p2m_ram_rw even though it could be subject of
another domain's foreign map?
Based on your previous e-mail, I would be fine with that on Arm.
This brings me to the next question. Do you expect set_special_p2m_entry
to take a reference on the page?
If not, we may run into some troubles because AFAICT you can map twice
the ioreq page in a guest but reference will only be taken on the
allocation.
However, the unmap path will always drop a reference when removing the
page. This is because Xen at the moment, reference will not be taken on
mapping but allocation (we assume a page could not be mapped twice in a
guest).
Foreign mapping on Arm are a bit special because we get a reference on
mapping them and will drop it when the mapping disappear. So we would
not have any problem there.
Any thoughts?
--
Julien Grall
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