linux-kernel - Re: Question about reserved

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Message-ID: <CAKgT0UcdjjzavB65QVcuyPUJpaCXTG67y29JVbhQCEg0oo2+=A@mail.gmail.com>
Date:   Thu, 8 Jun 2023 11:17:58 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Ashok Raj <ashok_raj@...ux.intel.com>,
        Baolu Lu <baolu.lu@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>, iommu@...ts.linux.dev,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: Question about reserved_regions w/ Intel IOMMU

On Thu, Jun 8, 2023 at 11:02 AM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2023-06-08 18:10, Alexander Duyck wrote:

<...>

> > As a part of going down that rabbit hole I realized that the
> > reserved_regions seems to only list the MSI reservation. However after
> > digging a bit deeper it seems like there is code to reserve the memory
> > behind the root complex in the IOVA but it doesn't look like that is
> > visible anywhere and is the piece I am currently trying to sort out.
> > What I am working on is trying to figure out if the system that is
> > failing is actually reserving that memory region in the IOVA, or if
> > that is somehow not happening in our test setup.
>
> How old's the kernel? Before 5.11, intel-iommu wasn't hooked up to
> iommu-dma so didn't do quite the same thing - it only reserved whatever
> specific PCI memory resources existed at boot, rather than the whole
> window as iommu-dma does. Either way, ftrace on reserve_iova() (or just
> whack a print in there) should suffice to see what's happened.
>
> Robin.

We are working with a 5.12 kernel. I will do some digging. We may be
able to backport some fixes if needed.

Thanks,

- Alex