From: Joerg Roedel <joro@8bytes.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Stuart Yoder <stuyoder@gmail.com>,
rafael@kernel.org, David Airlie <airlied@linux.ie>,
linux-pci@vger.kernel.org,
Thierry Reding <thierry.reding@gmail.com>,
Diana Craciun <diana.craciun@oss.nxp.com>,
Dmitry Osipenko <digetx@gmail.com>, Will Deacon <will@kernel.org>,
Ashok Raj <ashok.raj@intel.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
Christoph Hellwig <hch@infradead.org>,
Kevin Tian <kevin.tian@intel.com>,
Chaitanya Kulkarni <kch@nvidia.com>,
Alex Williamson <alex.williamson@redhat.com>,
kvm@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
Dan Williams <dan.j.williams@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Cornelia Huck <cohuck@redhat.com>,
linux-kernel@vger.kernel.org, Li Yang <leoyang.li@nxp.com>,
iommu@lists.linux-foundation.org,
Jacob jun Pan <jacob.jun.pan@intel.com>,
Daniel Vetter <daniel@ffwll.ch>,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v1 5/8] iommu/amd: Use iommu_attach/detach_device()
Date: Tue, 15 Feb 2022 10:11:01 +0100 [thread overview]
Message-ID: <YgtuJQhY8SNlv9/6@8bytes.org> (raw)
In-Reply-To: <20220214150059.GE4160@nvidia.com>
On Mon, Feb 14, 2022 at 11:00:59AM -0400, Jason Gunthorpe wrote:
> On Mon, Feb 14, 2022 at 03:23:07PM +0100, Joerg Roedel wrote:
>
> > Device drivers calling into iommu_attach_device() is seldom a good
> > idea. In this case the sound device has some generic hardware
> > interface so that an existing sound driver can be re-used. Making this
> > driver call iommu-specific functions for some devices is something hard
> > to justify.
>
> Er, so this is transparent to the generic sound device? I guess
> something fixed up the dma_api on that device to keep working?
Right, this is completly transparent to the sound device. The IOMMU code
will not set dma_ops on the device because it uses a direct mapping and
so the standard implementation will be used.
> But, then, the requirement is that nobody is using the dma API when we
> make this change?
That is the tricky part. DMA-API keeps working after the change is made,
because the new domain is also direct mapped. The new domain just has
the ability to assign host page-tables to device PASIDs, so that DMA
requests with a PASID TLP will be remapped.
It was actually a requirement for this code that when it jumps in, the
DMA-API mappings stay live. And the reason a direct mapping is used at
all is that the page-table walker of the IOMMU is a two-dimensional
walker, which will treat the addresses found in the host page-tables as
IO-virtual an translates them through the underlying page-table. So to
use host-pagetables the underlying mapping must be direct mapped.
> I don't think it matters how big/small the group is, only that when we
> change the domain we know everything flowing through the domain is
> still happy.
Yes, that matters. The group size matters too for DMA-API performance.
If two devices compete for the same lock in the allocator and/or the
same cached magazines, things will slow down. That only matters for
high-throughput devices, but still...
Regards,
Joerg
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2022-02-15 9:11 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-06 2:20 [PATCH v1 0/8] Scrap iommu_attach/detach_group() interfaces Lu Baolu
2022-01-06 2:20 ` [PATCH v1 1/8] iommu: Add iommu_group_replace_domain() Lu Baolu
2022-01-06 17:06 ` Jason Gunthorpe via iommu
2022-01-07 0:26 ` Lu Baolu
2022-02-14 12:09 ` Robin Murphy
2022-02-14 12:45 ` Jason Gunthorpe via iommu
2022-02-14 14:10 ` Robin Murphy
2022-02-14 14:56 ` Jason Gunthorpe via iommu
2022-02-14 16:38 ` Robin Murphy
2022-02-14 17:25 ` Jason Gunthorpe via iommu
2022-01-06 2:20 ` [PATCH v1 2/8] vfio/type1: Use iommu_group_replace_domain() Lu Baolu
2022-01-06 2:20 ` [PATCH v1 3/8] iommu: Extend iommu_at[de]tach_device() for multi-device groups Lu Baolu
2022-01-06 17:22 ` Jason Gunthorpe via iommu
2022-01-07 1:14 ` Lu Baolu
2022-01-07 1:19 ` Jason Gunthorpe via iommu
2022-02-14 11:39 ` Joerg Roedel
2022-02-14 13:03 ` Jason Gunthorpe via iommu
2022-02-14 14:39 ` Joerg Roedel
2022-02-14 15:18 ` Robin Murphy
2022-02-14 15:46 ` Jason Gunthorpe via iommu
2022-02-15 8:58 ` Joerg Roedel
2022-02-15 13:47 ` Jason Gunthorpe via iommu
2022-02-16 6:28 ` Lu Baolu
2022-02-16 13:54 ` Jason Gunthorpe via iommu
2022-01-06 2:20 ` [PATCH v1 4/8] drm/tegra: Use iommu_attach/detatch_device() Lu Baolu
2022-01-06 2:20 ` [PATCH v1 5/8] iommu/amd: Use iommu_attach/detach_device() Lu Baolu
2022-01-06 14:33 ` Jason Gunthorpe via iommu
2022-01-07 0:23 ` Lu Baolu
2022-02-14 11:27 ` Joerg Roedel
2022-02-14 13:15 ` Jason Gunthorpe via iommu
2022-02-14 13:40 ` Joerg Roedel
2022-02-14 14:02 ` Jason Gunthorpe via iommu
2022-02-14 14:23 ` Joerg Roedel
2022-02-14 15:00 ` Jason Gunthorpe via iommu
2022-02-15 9:11 ` Joerg Roedel [this message]
2022-02-15 13:02 ` Robin Murphy
2022-02-15 14:37 ` Jason Gunthorpe via iommu
2022-01-06 2:20 ` [PATCH v1 6/8] gpu/host1x: " Lu Baolu
2022-01-06 15:35 ` Jason Gunthorpe via iommu
2022-01-07 0:35 ` Lu Baolu
2022-01-07 0:48 ` Jason Gunthorpe via iommu
2022-01-07 1:19 ` Lu Baolu
2022-01-06 2:20 ` [PATCH v1 7/8] media: staging: media: tegra-vde: " Lu Baolu
2022-01-06 2:20 ` [PATCH v1 8/8] iommu: Remove iommu_attach/detach_group() Lu Baolu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YgtuJQhY8SNlv9/6@8bytes.org \
--to=joro@8bytes.org \
--cc=airlied@linux.ie \
--cc=alex.williamson@redhat.com \
--cc=ashok.raj@intel.com \
--cc=bhelgaas@google.com \
--cc=cohuck@redhat.com \
--cc=dan.j.williams@intel.com \
--cc=daniel@ffwll.ch \
--cc=diana.craciun@oss.nxp.com \
--cc=digetx@gmail.com \
--cc=gregkh@linuxfoundation.org \
--cc=hch@infradead.org \
--cc=iommu@lists.linux-foundation.org \
--cc=jacob.jun.pan@intel.com \
--cc=jgg@nvidia.com \
--cc=jonathanh@nvidia.com \
--cc=kch@nvidia.com \
--cc=kevin.tian@intel.com \
--cc=kvm@vger.kernel.org \
--cc=leoyang.li@nxp.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=rafael@kernel.org \
--cc=robin.murphy@arm.com \
--cc=stuyoder@gmail.com \
--cc=thierry.reding@gmail.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).