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

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Message-ID: <CABe79T7Oqs4KcX+m3EWXioDHAZ0xnRi+D0riPDDKWA4u1=nu+g@mail.gmail.com>
Date:   Wed, 1 May 2019 21:02:30 +0530
From:   Srinath Mannam <srinath.mannam@...adcom.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Joerg Roedel <joro@...tes.org>, poza@...eaurora.org,
        Ray Jui <rjui@...adcom.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 0/3] PCIe Host request to reserve IOVA

Hi Lorenzo,

Thanks a lot. Please see my reply below.

On Wed, May 1, 2019 at 7:24 PM Lorenzo Pieralisi
<lorenzo.pieralisi@....com> wrote:
>
> On Wed, May 01, 2019 at 02:20:56PM +0100, Robin Murphy wrote:
> > On 2019-05-01 1:55 pm, Bjorn Helgaas wrote:
> > > On Wed, May 01, 2019 at 12:30:38PM +0100, Lorenzo Pieralisi 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.
> > > > >
> > > > > 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(-)
> > > >
> > > > Bjorn, Joerg,
> > > >
> > > > this series should not affect anything in the mainline other than its
> > > > consumer (ie patch 3); if that's the case should we consider it for v5.2
> > > > and if yes how are we going to merge it ?
> > >
> > > I acked the first one
> > >
> > > Robin reviewed the second
> > > (https://lore.kernel.org/lkml/e6c812d6-0cad-4cfd-defd-d7ec427a6538@arm.com)
> > > (though I do agree with his comment about DMA_BIT_MASK()), Joerg was OK
> > > with it if Robin was
> > > (https://lore.kernel.org/lkml/20190423145721.GH29810@8bytes.org).
> > >
> > > Eric reviewed the third (and pointed out a typo).
> > >
> > > My Kconfiggery never got fully answered -- it looks to me as though it's
> > > possible to build pcie-iproc without the DMA hole support, and I thought
> > > the whole point of this series was to deal with those holes
> > > (https://lore.kernel.org/lkml/20190418234241.GF126710@google.com).  I would
> > > have expected something like making pcie-iproc depend on IOMMU_SUPPORT.
> > > But Srinath didn't respond to that, so maybe it's not an issue and it
> > > should only affect pcie-iproc anyway.
> >
> > Hmm, I'm sure I had at least half-written a reply on that point, but I
> > can't seem to find it now... anyway, the gist is that these inbound
> > windows are generally set up to cover the physical address ranges of DRAM
> > and anything else that devices might need to DMA to. Thus if you're not
> > using an IOMMU, the fact that devices can't access the gaps in between
> > doesn't matter because there won't be anything there anyway; it only
> > needs mitigating if you do use an IOMMU and start giving arbitrary
> > non-physical addresses to the endpoint.
>
> So basically there is no strict IOMMU_SUPPORT dependency.
Yes, without IOMMU_SUPPORT, all inbound addresses will fall inside dma-ranges.
Issue is only in the case of IOMMU enable, this patch will address by
reserving non-allowed
address (holes of dma-ranges) by reserving them.
>
> > > So bottom line, I'm fine with merging it for v5.2.  Do you want to merge
> > > it, Lorenzo, or ...?
> >
> > This doesn't look like it will conflict with the other DMA ops and MSI
> > mapping changes currently in-flight for iommu-dma, so I have no
> > objection to it going through the PCI tree for 5.2.
>
> I will update the DMA_BIT_MASK() according to your review and fix the
> typo Eric pointed out and push out a branch - we shall see if we can
> include it for v5.2.
I will send new patches with the change DMA_BIT_MASK() and typo along
with Bjorn's comment in PATCH-1.

Regards,
Srinath.
>
> Thanks,
> Lorenzo