Re: [PATCH] PCI/P2PDMA: Root complex whitelist should not apply when an IOMMU is present

["Koenig, Christian" <Christian.Koenig@amd.com>]

Am 23.05.19 um 11:43 schrieb Christoph Hellwig:
> [CAUTION: External Email]
>
> On Thu, May 23, 2019 at 08:12:18AM +0000, Koenig, Christian wrote:
>>> Are you DMA-mapping the addresses outside the P2PDMA code? If so there's
>>> a huge mismatch with the existing users of P2PDMA (nvme-fabrics). If
>>> you're not dma-mapping then I can't see how it could work because the
>>> IOMMU should reject any requests to access those addresses.
>> Well, we are using the DMA API (dma_map_resource) for this. If the P2P
>> code is not using this then I would rather say that the P2P code is
>> actually broken.
>>
>> Adding Christoph as well, cause he is usually the one discussion stuff
>> like that with me.
> Heh.  Actually dma_map_resource-ish APIs are the right thing to do,
> but I'm not sure how you managed to be able to use it for PCIe P2P
> yet, as it fails to account for any difference in the PCIe level
> "physical" address with the hosts view of "physical" addresses.
>
> Do these offsets now how up on AMD platforms?  Do you adjust for them
> elsewhere?

I don't adjust the address manually anywhere. I just call 
dma_map_resource() and use the resulting DMA address to access the other 
devices PCI BAR.

At least on my test system (AMD CPU + AMD GPUs) this seems to work 
totally fine. Currently trying to find time and an Intel box to test it 
there as well.

Regards,
Christian.