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

Eric Auger
2015-03-20T14:13:15Z

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@linaro.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@linux.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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