Re: [PATCH v3 5/8] iommu/vt-d: Implement def_domain_type iommu ops entry

Lu Baolu
2019-04-30T02:18:32Z

Hi Christoph,

On 4/30/19 4:03 AM, Christoph Hellwig wrote:
>> @@ -3631,35 +3607,30 @@ static int iommu_no_mapping(struct device *dev)
>> if (iommu_dummy(dev))
>> return 1;
>>
>> - if (!iommu_identity_mapping)
>> - return 0;
>> -
>
> FYI, iommu_no_mapping has been refactored in for-next:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu.git/commit/?h=x86/vt-d&id=48b2c937ea37a3bece0094b46450ed5267525289

Oh, yes! Thanks for letting me know this. Will rebase the code.

>
>> found = identity_mapping(dev);
>> if (found) {
>> + /*
>> + * If the device's dma_mask is less than the system's memory
>> + * size then this is not a candidate for identity mapping.
>> + */
>> + u64 dma_mask = *dev->dma_mask;
>> +
>> + if (dev->coherent_dma_mask &&
>> + dev->coherent_dma_mask < dma_mask)
>> + dma_mask = dev->coherent_dma_mask;
>> +
>> + if (dma_mask < dma_get_required_mask(dev)) {
>
> I know this is mostly existing code moved around, but it really needs
> some fixing. For one dma_get_required_mask is supposed to return the
> required to not bounce mask for the given device. E.g. for a device
> behind an iommu it should always just return 32-bit. If you really
> want to check vs system memory please call dma_direct_get_required_mask
> without the dma_ops indirection.
>
> Second I don't even think we need to check the coherent_dma_mask,
> dma_direct is pretty good at always finding memory even without
> an iommu.
>
> Third this doesn't take take the bus_dma_mask into account.
>
> This probably should just be:
>
> if (min(*dev->dma_mask, dev->bus_dma_mask) <
> dma_direct_get_required_mask(dev)) {

Agreed and will add this in the next version.

Best regards,
Lu Baolu