Re: Device pass-through

[Gordon Messmer <yinyang@eburg.com>]

Thanks, Alex.  I really appreciate the reply.

On 01/03/2012 01:34 PM, Alex Williamson wrote:
> This is actually the GART aperture, which Linux will try to use as an
> IOMMU.  You can pretty much ignore this, but it may be wasting memory
> for no good reason if it's really hiding usable memory and allocating a
> bounce buffer area.

It does look that way, but I doubt I'll miss it.  Would you suggest that 
I boot with swiotlb=0 ?

> The host is potentially exposed to a malicious guest trying to trigger
> MSI interrupts for denial of service or exploit probing.  If you trust
> your guest, it's safe to allow this.

I do.  It's a Fedora guest that I'm personally using.  Suppose I didn't. 
  My kernel was built with CONFIG_INTR_REMAP=y but the kernel said 
"kvm_iommu_map_guest: No interrupt remapping support, disallowing device 
assignment."  Does that mean that the motherboard doesn't support 
interrupt remapping?

>> 4: What do these errors mean, and is there any way I can correct the
>> problem?
>>> create_userspace_phys_mem: File exists
>>> assigned_dev_iomem_map: Error: create new mapping failed
>
> Might mean the resources for the graphics card are getting mapped to
> overlap with guest memory.  What does lspci -v for the graphics card
> show?  More recent changes upstream might make better use of the space
> we have for devices, might be worth a test.

05:00.0 VGA compatible controller: ATI Technologies Inc RV620 PRO
		[Radeon HD 3470] (prog-if 00 [VGA controller])
	Subsystem: Dell Device 3243
	Flags: fast devsel, IRQ 17
	Memory at c0000000 (64-bit, prefetchable) [disabled] [size=256M]
	Memory at fd9f0000 (64-bit, non-prefetchable)
		[disabled] [size=64K]
	I/O ports at ae00 [disabled] [size=256]
	Expansion ROM at fd900000 [disabled by cmd] [size=128K]
	Capabilities: [50] Power Management version 3
	Capabilities: [58] Express Legacy Endpoint, MSI 00
	Capabilities: [a0] MSI: Enable- Count=1/1 Maskable- 64bit+
	Capabilities: [100] Vendor Specific Information <?>
	Kernel modules: radeon