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Re: [Xen-devel] [PATCH for-4.13] AMD/IOMMU: honour IR setting while pre-filling DTEs
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 26 Nov 2019 14:34:07 +0000
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- Cc: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 26 Nov 2019 14:34:13 +0000
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On 26/11/2019 14:14, Jan Beulich wrote:
> On 26.11.2019 13:25, Andrew Cooper wrote:
>> On 26/11/2019 08:42, Jan Beulich wrote:
>>> On 25.11.2019 22:05, Igor Druzhinin wrote:
>>>> --- a/xen/drivers/passthrough/amd/iommu_init.c
>>>> +++ b/xen/drivers/passthrough/amd/iommu_init.c
>>>> @@ -1279,7 +1279,7 @@ static int __init amd_iommu_setup_device_table(
>>>> for ( bdf = 0, size /= sizeof(*dt); bdf < size; ++bdf )
>>>> dt[bdf] = (struct amd_iommu_dte){
>>>> .v = true,
>>>> - .iv = true,
>>>> + .iv = iommu_intremap,
>>> This was very intentionally "true", and ignoring "iommu_intremap":
>> Deliberate or not, it is a regression from 4.12.
> I accept it's a regression (which wants fixing), but I don't think
> this is the way to address is. I could be convinced by good
> arguments, though.
>
>> Booting with iommu=no-intremap is a common debugging technique, and that
>> means no interrupt remapping anywhere in the system, even for
>> supposedly-unused DTEs.
> Whether IV=1 or IV=0, there's no interrupt _remapping_ with this
> option specified. There's some interrupt _blocking_, yes. It's
> not immediately clear to me whether this is a good or a bad thing.
You're attempting to argue semantics. Blocking is a special case remapping.
"iommu=no-intremap" (for better or worse, naming wise) refers to the
interrupt mediation functionality in the IOMMU, and means "don't use any
of it". Any other behaviour is a regression.
~Andrew
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