[PATCH v2] powerpc/iommu: DMA address offset is incorrectly calculated with 2MB TCEs

Michael Ellerman mpe at ellerman.id.au
Thu May 4 15:10:14 AEST 2023

Gaurav Batra <gbatra at linux.vnet.ibm.com> writes:
> Hello Michael,
> I was looking into the Bug: 199106 
> (https://bugzilla.linux.ibm.com/show_bug.cgi?id=199106).
> In the Bug, Mellanox driver was timing out when enabling SRIOV device.
> I tested, Alexey's patch and it fixes the issue with Mellanox driver. 
> The down side
> to Alexey's fix is that even a small memory request by the driver will 
> be aligned up
> to 2MB. In my test, the Mellanox driver is issuing multiple requests of 
> 64K size.
> All these will get aligned up to 2MB, which is quite a waste of resources.

OK. I guess we should use your patch then.

It's not ideal as it means the device can potentially read/write to
memory it shouldn't, but 2MB is a lot to waste for a 64K alloc.

> In any case, both the patches work. Let me know which approach you 
> prefer. In case
> we decide to go with my patch, I just realized that I need to fix 
> nio_pages in
> iommu_free_coherent() as well.

Can you send a v3 with that fixed please.


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