Re: [Xen-devel] [PATCH for-4.13] AMD/IOMMU: honour IR setting while pre-filling DTEs

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan

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