RE: [Xen-devel] RE: Intel IOMMU: Assigning IGD device: 00:02.1 on some machines, causes Xen to freeze for >2mins because of RMRR mappings

["Kay, Allen M" <allen.m.kay@xxxxxxxxx>]

While you are at it, please also add memory attribute to the API too.  In the 
future, we might want to map pages as read only or some other attribute instead 
of just RW.

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Han, Weidong
Sent: Sunday, November 29, 2009 6:30 PM
To: Tom Rotenberg; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] RE: Intel IOMMU: Assigning IGD device: 00:02.1 on some 
machines, causes Xen to freeze for >2mins because of RMRR mappings

Tom,

Yes, you can add an API to map batches of pages instead of mapping each page in 
a separate call.

RMRR regions of USB controller is ignored because they won't be used in guest. 
The RMRR 0x7dc00000 to 0x80000000 is shared by 00:02.0 and 00:02.1, it will be 
used by IGD in guest. But you can have a try to ignore it for 00:02.1.


Regards,
Weidong

-----Original Message-----
From: Tom Rotenberg [mailto:tom.rotenberg@xxxxxxxxx] 
Sent: Monday, November 30, 2009 1:56 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Cc: Han, Weidong
Subject: Intel IOMMU: Assigning IGD device: 00:02.1 on some machines, causes 
Xen to freeze for >2mins because of RMRR mappings

Hi All,

I am using a Dell E6400 machine, with IGD (Intel graphics device),
which i'm trying to pass-through into a domU with Windows XP. When i
assign only the 00:02.0 device, it seems to work ok, but when i try to
assign the 00:02.1 device, the whole machine seems to freeze form more
then 2 mins, causing a lot of messgaes in dom0, such as: SATA doesn't
respond, etc.

After some analysis i made, i discovered the followings:
* When calling the (Intel) iommu_assign_device, it checks if the
device has any details in the RMRR table, and if so it calls the
'iommu_prepare_rmrr_dev()' function.
* The device 00:02.1 has an RMRR information, which details the whole
area between:  0x7dc00000 to 0x80000000  (it contains ~9000 pages)
* For each such page, Xen calls the 'intel_iommu_map_page()' function.
This causes the hypercall to take a lot of time to process, and this
makes dom0 to stop getting responds from devices, such as SATA, etc,,
which may lead to a whole system  crash.

My question are:
1. Can this hypercall be in some way preemptive, so it won't stuck the
whole system (i noticed that there are other hypercalls, which are
preemptive) ?
2. Why can't the mapping of the pages, be done in batches of pages,
instead of mapping each page in a separate call to
'intel_iommu_map_page()' ?
3. i noticed that for USB devices, the code there ignores the USB
RMRR... can this be done also for the 00:02.1 device?

Tom

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