Re: Question about reserved_regions w/ Intel IOMMU

From: Alexander Duyck <alexander.duyck@gmail.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Ashok Raj <ashok_raj@linux.intel.com>,
	Baolu Lu <baolu.lu@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-pci <linux-pci@vger.kernel.org>,
	iommu@lists.linux.dev, Ashok Raj <ashok.raj@intel.com>
Subject: Re: Question about reserved_regions w/ Intel IOMMU
Date: Thu, 8 Jun 2023 11:17:58 -0700	[thread overview]
Message-ID: <CAKgT0UcdjjzavB65QVcuyPUJpaCXTG67y29JVbhQCEg0oo2+=A@mail.gmail.com> (raw)
In-Reply-To: <7f1797b1-cd50-3c8d-59ff-8ce82ef1adb4@arm.com>

On Thu, Jun 8, 2023 at 11:02 AM Robin Murphy <robin.murphy@arm.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