linux-kernel - Re: [PATCH v2 00/15] PCI/iommu: Fix DMA alias problems

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Date:	Thu, 15 May 2014 07:40:25 +0800
From:	Andrew Cooks <acooks@...il.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	"open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
	"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 00/15] PCI/iommu: Fix DMA alias problems

Hi Alex

On Fri, May 9, 2014 at 11:28 PM, Alex Williamson
<alex.williamson@...hat.com> wrote:
> ....
>
> Original description:
>
> This series attempts to fix a couple issues we've had outstanding in
> the PCI/IOMMU code for a while.  The first issue is with devices that
> use the wrong requester ID for DMA transactions.  We already have a
> sort of half-baked attempt to fix this for several Ricoh devices, but
> the fix only helps them be useful through IOMMU groups, not the
> general DMA case.  There are also several Marvell devices which use
> use a different wrong requester ID and don't even fit into the DMA
> source idea.  This series creates a DMA alias iterator that will
> step through each possible alias of a device, allowing IOMMUs to
> insert mappings for both the device and its aliases.
>
> Hand-in-hand with this is our broken pci_find_upstream_pcie_bridge()
> function, which is known to blowup when it finds itself suddenly at
> a PCIe device without crossing a PCIe-to-PCI bridge (as identified by
> the PCIe capability).  It also likes to make the invalid assumption
> that a PCIe device never has its requester ID masked by any usptream
> bus.  We can fix this using the above new DMA alias iterator, since
> that's effectively what this function was meant to do.
>

There are two cases where the DMA requester id seems to use the wrong
slot (as opposed to function) in the patch I attached to
https://bugzilla.kernel.org/show_bug.cgi?id=42679
The original bug reports are listed in the patch.

Unfortunately, I wasn't able to get test feedback on those two cases,
but I'm wondering...
Did I understand correctly that a slot alias is something that could be needed?
If so, is it a variation of the PCIe-to-PCI bridge case that's already
covered or will it require a different approach?

Thanks,

a.
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