linux-kernel - Re: Question about reserved

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Message-ID: <CAKgT0UfMeVOz6AOqSvVvzpsedGDiXCNQrjM+4KDv7qJJ1orpsw@mail.gmail.com>
Date:   Wed, 7 Jun 2023 16:03:54 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>, iommu@...ts.linux.dev
Subject: Re: Question about reserved_regions w/ Intel IOMMU

On Wed, Jun 7, 2023 at 3:40 PM Alexander Duyck
<alexander.duyck@...il.com> wrote:
>
> I am running into a DMA issue that appears to be a conflict between
> ACS and IOMMU. As per the documentation I can find, the IOMMU is
> supposed to create reserved regions for MSI and the memory window
> behind the root port. However looking at reserved_regions I am not
> seeing that. I only see the reservation for the MSI.
>
> So for example with an enabled NIC and iommu enabled w/o passthru I am seeing:
> # cat /sys/bus/pci/devices/0000\:83\:00.0/iommu_group/reserved_regions
> 0x00000000fee00000 0x00000000feefffff msi
>
> Shouldn't there also be a memory window for the region behind the root
> port to prevent any possible peer-to-peer access?

Since the iommu portion of the email bounced I figured I would fix
that and provide some additional info.

I added some instrumentation to the kernel to dump the resources found
in iova_reserve_pci_windows. From what I can tell it is finding the
correct resources for the Memory and Prefetchable regions behind the
root port. It seems to be calling reserve_iova which is successfully
allocating an iova to reserve the region.

However still no luck on why it isn't showing up in reserved_regions.