linux-kernel - Re: Hardware support for vt-posted interrupts described in vt-directed-io-spec for assigned devices

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Date:	Fri, 20 Mar 2015 15:10:46 +0100
From:	Eric Auger <eric.auger@...aro.org>
To:	Alex Williamson <alex.williamson@...hat.com>,
	bk rakesh <rakeshbkrish@...il.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	jiang.liu@...ux.intel.com
Subject: Re: Hardware support for vt-posted interrupts described in vt-directed-io-spec
 for assigned devices

On 03/20/2015 03:04 PM, Alex Williamson wrote:
> On Fri, 2015-03-20 at 15:24 +0530, bk rakesh wrote:
>> Adding few more information regarding the setup which i had created to
>> test the vt-d posted interrupts for assigned devices,
>>
>> Hardware used for evaluating vt-posted interrupts
>>     cpu "E5-2620 v2 @ 2.10GHz" and "S2600CP server board"
>>
>> I had used kernel-3.18 patched with "KVM-VFIO IRQ forward
>> control(posted by eric.auger@...aro.org)",
> 
> IRQ forwarding in an ARM technology for handling level triggered
> interrupts, not Intel, not even x86.

Hi Alex,

Feng's series relies on few pacth files in "KVM-VFIO IRQ forward
control", basically for KVM_DEV_VFIO_DEVICE group introduction in
KVM-VFIO. This explains why you find some references to that patch here
I guess.

Best Regards

Eric

> 
>>  "hierarchy irqdomian(posted
>> by jiang.liu@...ux.intel.com)" and "VT-d Posted-Interrupts
>> support(http://lwn.net/Articles/626050/) and assigned the ixgbe 10G
>> NIC via vfio passthrough using qemu-kvm, But resulted in the following
>> dmesg output,
>>
>> [233783.657187] dmar: DRHD: handling fault status reg 602
>> [233783.662926] dmar: INTR-REMAP: Request device [[02:00.0] fault index 47
>> INTR-REMAP:[fault reason 36] Detected reserved fields in the IRTE entry
> 
> This suggests bugs in the patch series for setting bits that are
> reserved on the hardware in your test system.
> 
>> I had checked the hardware supported for posted interrupt capability
>> via capability register bit 59 (#define cap_pi_support(c)    (((c) >>
>> 59) & 1)),  as described in
>> "http://www.intel.com/content/www/us/en/embedded/technology/virtualization/vt-directed-io-spec.html",
>> Which resulted as not supported, Can anyone suggest that does this hw
>> support posted vt-d feature ?
> 
> Your own hardware is telling you that it doesn't support it.
> 
>>  if not then which one to use.
> 
> Personally I would have no expectation that any currently shipping
> hardware supports this feature.  If you watch one of GregKH's talks on
> how the Linux community works or follow development for a while, you'll
> see and hear that Intel will often pre-enable features before the
> hardware that supports it is available.  I suspect this is one of those
> features.  Thanks,
> 
> Alex
> 
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