Re: [PATCH v2 0/4] Make the iommu driver no-snoop block feature consistent

[Robin Murphy <robin.murphy@arm.com>]

On 2022-04-08 10:08, Tian, Kevin wrote:
>> From: Jason Gunthorpe <jgg@nvidia.com>
>> Sent: Friday, April 8, 2022 3:08 AM
>> On Thu, Apr 07, 2022 at 07:02:03PM +0100, Robin Murphy wrote:
>>> On 2022-04-07 18:43, Jason Gunthorpe wrote:
>>>> On Thu, Apr 07, 2022 at 06:03:37PM +0100, Robin Murphy wrote:
>>>>> At a glance, this all looks about the right shape to me now, thanks!
>>>>
>>>> Thanks!
>>>>
>>>>> Ideally I'd hope patch #4 could go straight to device_iommu_capable()
>> from
>>>>> my Thunderbolt series, but we can figure that out in a couple of weeks
>> once
>>>>
>>>> Yes, this does helps that because now the only iommu_capable call is
>>>> in a context where a device is available :)
>>>
>>> Derp, of course I have *two* VFIO patches waiting, the other one touching
>>> the iommu_capable() calls (there's still IOMMU_CAP_INTR_REMAP, which,
>> much
>>> as I hate it and would love to boot all that stuff over to
>>> drivers/irqchip,
>>
>> Oh me too...
>>
>>> it's not in my way so I'm leaving it be for now). I'll have to rebase that
>>> anyway, so merging this as-is is absolutely fine!
>>
>> This might help your effort - after this series and this below there
>> are no 'bus' users of iommu_capable left at all.
>>
> 
> Out of curiosity, while iommu_capable is being moved to a per-device
> interface what about irq_domain_check_msi_remap() below (which
> is also a global check)?

I suppose it could if anyone cared enough to make the effort - probably 
a case of resolving specific MSI domains for every device in the group, 
and potentially having to deal with hotplug later as well. 
Realistically, though, I wouldn't expect systems to have mixed 
capabilities in that regard (i.e. where the check would return false 
even though *some* domains support remapping), so there doesn't seem to 
be any pressing need to relax it.

Cheers,
Robin.

>> +static int vfio_iommu_device_ok(void *iommu_data, struct device *device)
>> +{
>> +	bool msi_remap;
>> +
>> +	msi_remap = irq_domain_check_msi_remap() ||
>> +		    iommu_capable(device->bus, IOMMU_CAP_INTR_REMAP);
>> +
>