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Date: Mon, 10 Jun 2024 08:38:49 -0300
From: Jason Gunthorpe <jgg@nvidia.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Vidya Sagar <vidyas@nvidia.com>, "corbet@lwn.net" <corbet@lwn.net>,
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	Robin Murphy <robin.murphy@arm.com>,
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Subject: Re: [PATCH V3] PCI: Extend ACS configurability
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On Fri, Jun 07, 2024 at 02:30:55PM -0500, Bjorn Helgaas wrote:
> "Correctly" is not quite the right word here; it's just a fact that
> the ACS settings determined at boot time result in certain IOMMU
> groups.  If the user desires different groups, it's not that something
> is "incorrect"; it's just that the user may have to accept less
> isolation to get the desired IOMMU groups.

That is not quite accurate.. There are HW configurations where ACS
needs to be a certain way for the HW to work with P2P at all. It isn't
just an optimization or the user accepts something, if they want P2P
at all they must get a ACS configuration appropriate for their system.

Jason