Forward to i915 mailing list and post the question again so people knows
what are the key concerns.
The background is that Linux community is going to collect and report
the reserved memory ranges of an assigned device to VFIO driver, and any
mapped address will be checked against the reserved ranges. If there's
any conflict, vifo will refuse the map request.
Unfortunately, when it comes Intel graphic device, the conflict happens.
That means address range mapped through vfio conflicts with the rmrr for
graphic device.
https://lkml.org/lkml/2018/6/5/760
The questions are 1) will the rmrr for graphic device still needs to be
reserved for BIOS or firmware use, when a device is going to be assigned
to user level? 2) if no, what's the check point, after which the rmrr is
unnecessary anymore?
Best regards,
Lu Baolu
On 5/9/19 5:14 PM, Zhang, Tina wrote:
Hi Baolu,
+Xiong
I think the root cause is that guest i915 needs to access RMRR. Xiong cooked a patch to disable the RMRR use in i915 guest, however that patch didn't get landed into the i915 upstream repo due to some concerns from i915 maintainers. Xiong can give us more backgrounds.
So agreed, need to ask the i915 folk for this.
BR,
Tina
-----Original Message-----
From: Yuan, Hang
Sent: Thursday, May 9, 2019 4:07 PM
To: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>; Tian, Kevin <kevin.tian@xxxxxxxxx>;
Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>; Zhang, Tina
<tina.zhang@xxxxxxxxx>; Lu, Baolu <baolu.lu@xxxxxxxxx>; Liu, Yi L
<yi.l.liu@xxxxxxxxx>
Subject: RE: IOMMU RMRR for Intel graphic device
Hi Baolu, as Kevin suggested, would you like to ask i915 people in their
mailing list intel-gfx@xxxxxxxxxxxxxxxxxxxxx?
Regards,
Henry
-----Original Message-----
From: Lu Baolu [mailto:baolu.lu@xxxxxxxxxxxxxxx]
Sent: Thursday, May 9, 2019 2:42 PM
To: Tian, Kevin <kevin.tian@xxxxxxxxx>; Zhenyu Wang
<zhenyuw@xxxxxxxxxxxxxxx>; Zhang, Tina <tina.zhang@xxxxxxxxx>; Yuan,
Hang <hang.yuan@xxxxxxxxx>; Lu, Baolu <baolu.lu@xxxxxxxxx>; Liu, Yi L
<yi.l.liu@xxxxxxxxx>
Cc: baolu.lu@xxxxxxxxxxxxxxx
Subject: Re: IOMMU RMRR for Intel graphic device
Hi,
+Tina and Henry and cc more people
The background is that Linux community is going to collect and report
the reserved memory ranges of an assigned device to VFIO driver, and
any mapped address will be checked against the reserved ranges. If
there's any conflict, vifo will refuse the map request.
Unfortunately, when it comes Intel graphic device, the conflict happens.
That means address range mapped through vfio conflicts with the rmrr
for graphic device.
https://lkml.org/lkml/2018/6/5/760
The questions are 1) will the rmrr for graphic device still needs to
be reserved for BIOS or firmware use, when a device is going to be
assigned to user level? 2) if no, what's the check point, after which
the rmrr is unnecessary anymore?
Best regards,
Lu Baolu
On 5/6/19 2:16 PM, Tian, Kevin wrote:
this should better be asked to i915 guys, since it's not
virtualization related. :-)
One caveat, iirc, i915 driver tries to reuse stolen memory (covered
by
RMRR) even after boot time. take it as if another type of memory
resource. If true I'm afraid this might be a gap to your proposal.
Since nothing confidential, possibly you can directly discuss in
community.
From: Lu Baolu [mailto:baolu.lu@xxxxxxxxxxxxxxx]
Sent: Thursday, May 2, 2019 2:45 PM
Ping...
Any comments? This has been postponed in the community for a long
time.
We need to response this as soon as possible.
Best regards,
Lu Baolu
On 4/29/19 1:19 PM, Lu Baolu wrote:
Hi Zhenyu,
As we discussed, BIOS always exports IOMMU reserved memory
regions
for (a.k.a. RMRR in vt-d spec) Intel integrated graphic device.
This caused some problems when we pass-through such graphic
devices to
user level.
I am about to propose something to the community so that a RMRR
for graphic devices could be explicitly canceled as long as the
driver
(i915 or vfio) knows that the RMRR will never be used by BIOS
anymore.
The same story happens for USB host controller devices. And since
we know that BIOS will stop using that memory region as soon as
the driver clears the SMI bits.
So the question is, can graphic driver know when the RMRR for
graphic could be canceled?
Best regards,
Lu Baolu
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