Re: [PATCH v4 0/3] PCIe Host request to reserve IOVA

From: Srinath Mannam <srinath.mannam@broadcom.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>,
	Joerg Roedel <joro@8bytes.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	poza@codeaurora.org, Ray Jui <rjui@broadcom.com>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
	linux-pci@vger.kernel.org, iommu@lists.linux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 0/3] PCIe Host request to reserve IOVA
Date: Tue, 16 Apr 2019 17:28:36 +0530	[thread overview]
Message-ID: <CABe79T7h9t_Obmo3+B0MHgLZ4ff9GxpBBBLGtSf0C=zmLrWVBQ@mail.gmail.com> (raw)
In-Reply-To: <20190412223409.GB126710@google.com>

Hi Bjorn,

Thanks for review. Please find my reply below.

On Sat, Apr 13, 2019 at 4:04 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Fri, Apr 12, 2019 at 08:43:32AM +0530, Srinath Mannam wrote:
> > Few SOCs have limitation that their PCIe host can't allow few inbound
> > address ranges. Allowed inbound address ranges are listed in dma-ranges
> > DT property and this address ranges are required to do IOVA mapping.
> > Remaining address ranges have to be reserved in IOVA mapping.
>
> If I understand correctly, devices below these PCIe host bridges can
> DMA only to the listed address ranges, and you prevent devices from
> doing DMA to the holes between the listed ranges by reserving the
> holes in dma-iommu.
Yes, devices below these PCIe host bridges can DMA only to the listed
address ranges,
and this patch prevents to allocate DMA(IOVA) addresses in the holes
of listed ranges.
>
> Apparently there's something that makes sure driver dma_map_*() always
> goes through dma-iommu?  I traced as far as seeing that dma-iommu
> depends on CONFIG_IOMMU_DMA, and that arm64 selects CONFIG_IOMMU_DMA
> if CONFIG_IOMMU_SUPPORT, but then the trail got cold.  I didn't see
> what selects CONFIG_IOMMU_SUPPORT.
IOMMU_SUPPORT depends on MMU.
>
> This does look like what Robin suggested, as far as I can tell.
> Hopefully he'll take a look and give his reviewed-by.  Thanks for
> persevering!
Thank you.

Regards,
Srinath.
>
> > PCIe Host driver of those SOCs has to list resource entries of allowed
> > address ranges given in dma-ranges DT property in sorted order. This
> > sorted list of resources will be processed and reserve IOVA address for
> > inaccessible address holes while initializing IOMMU domain.
> >
> > This patch set is based on Linux-5.0-rc2.
> >
> > Changes from v3:
> >   - Addressed Robin Murphy review comments.
> >     - pcie-iproc: parse dma-ranges and make sorted resource list.
> >     - dma-iommu: process list and reserve gaps between entries
> >
> > Changes from v2:
> >   - Patch set rebased to Linux-5.0-rc2
> >
> > Changes from v1:
> >   - Addressed Oza review comments.
> >
> > Srinath Mannam (3):
> >   PCI: Add dma_ranges window list
> >   iommu/dma: Reserve IOVA for PCIe inaccessible DMA address
> >   PCI: iproc: Add sorted dma ranges resource entries to host bridge
> >
> >  drivers/iommu/dma-iommu.c           | 19 ++++++++++++++++
> >  drivers/pci/controller/pcie-iproc.c | 44 ++++++++++++++++++++++++++++++++++++-
> >  drivers/pci/probe.c                 |  3 +++
> >  include/linux/pci.h                 |  1 +
> >  4 files changed, 66 insertions(+), 1 deletion(-)
> >
> > --
> > 2.7.4
> >