Re: [PATCH v4 04/14] PCI/P2PDMA: Clear ACS P2P flags for all devices behind switches

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On 5/11/2018 4:24 PM, Stephen  Bates wrote:
All

  Alex (or anyone else) can you point to where IOVA addresses are generated?

A case of RTFM perhaps (though a pointer to the code would still be appreciated).

https://www.kernel.org/doc/Documentation/Intel-IOMMU.txt

Some exceptions to IOVA
-----------------------
Interrupt ranges are not address translated, (0xfee00000 - 0xfeefffff).
The same is true for peer to peer transactions. Hence we reserve the
address from PCI MMIO ranges so they are not allocated for IOVA addresses.

Hmm, except I'm not sure how to interpret that. It sounds like there can't be an IOVA address that overlaps with the PCI MMIO range which is good and what I'd expect.

But for peer to peer they say they don't translate the address which implies to me that the intention is for a peer to peer address to not be mapped in the same way using the dma_map interface (of course though if you were using ATS you'd want this for sure). Unless the existing dma_map command's notice a PCI MMIO address and handle them differently, but I don't see how.

Logan




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