From: Nicolin Chen <nicolinc@nvidia.com>
To: "jgg@nvidia.com" <jgg@nvidia.com>, "Tian, Kevin" <kevin.tian@intel.com>
Cc: "will@kernel.org" <will@kernel.org>,
"robin.murphy@arm.com" <robin.murphy@arm.com>,
"suravee.suthikulpanit@amd.com" <suravee.suthikulpanit@amd.com>,
"joro@8bytes.org" <joro@8bytes.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
"Liu, Yi L" <yi.l.liu@intel.com>,
"eric.auger@redhat.com" <eric.auger@redhat.com>,
"vasant.hegde@amd.com" <vasant.hegde@amd.com>,
"jon.grimm@amd.com" <jon.grimm@amd.com>,
"santosh.shukla@amd.com" <santosh.shukla@amd.com>,
"Dhaval.Giani@amd.com" <Dhaval.Giani@amd.com>,
"shameerali.kolothum.thodi@huawei.com"
<shameerali.kolothum.thodi@huawei.com>
Subject: Re: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl
Date: Thu, 23 May 2024 22:40:07 -0700 [thread overview]
Message-ID: <ZlAoN3s96HL7ROth@nvidia.com> (raw)
In-Reply-To: <BN9PR11MB5276A897A5386DFAC9A35F9D8CF42@BN9PR11MB5276.namprd11.prod.outlook.com>
On Thu, May 23, 2024 at 06:42:56AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Saturday, April 13, 2024 11:47 AM
> >
> > Introduce a new ioctl to set a per-viommu device virtual id that should be
> > linked to the physical device id (or just a struct device pointer).
> >
> > Since a viommu (user space IOMMU instance) can have multiple devices
>
> this is true...
>
> > while
> > it's not ideal to confine a device to one single user space IOMMU instance
> > either, these two shouldn't just do a 1:1 mapping. Add two xarrays in
>
> ...but why would one device link to multiple viommu instances?
That's a suggestion from Jason, IIRC, to avoid limiting a device
to a single viommu, though I can't find out the source at this
moment.
Jason, would you mind shed some light here?
> Or is it referring to Tegra194 as arm-smmu-nvidia.c tries to support?
Not actual. It's an SMMUv2 driver, which is not in our plan for
virtualization at this moment. And that driver is essentially a
different "compatible" string as a unique SMMUv2 implementation.
> btw there is a check in the following code:
>
> + if (viommu->iommu_dev != idev->dev->iommu->iommu_dev) {
> + rc = -EINVAL;
> + goto out_put_viommu;
> + }
>
> I vaguely remember an earlier discussion about multiple vSMMU instances
> following the physical SMMU topology, but don't quite recall the exact
> reason.
>
> What is the actual technical obstacle prohibiting one to put multiple
> VCMDQ's from different SMMU's into one vIOMMU instance?
Because a VCMDQ passthrough involves a direct mmap of a HW MMIO
page to the guest-level MMIO region. The MMIO page provides the
read/write of queue's head and tail indexes.
With a single pSMMU and a single vSMMU, it's simply 1:1 mapping.
With a multi-pSMMU and a single vSMMU, the single vSMMU will see
one guest-level MMIO region backed by multiple physical pages.
Since we are talking about MMIO, technically it cannot select the
corresponding MMIO page to the device, not to mention we don't
really want VMM to involve, i.e. no VM exist, when using VCMDQ.
So, there must be some kind of multi-instanced carriers to hold
those MMIO pages, by attaching devices behind different pSMMUs to
corresponding carriers. And today we have VIOMMU as the carrier.
One step back, even without VCMDQ feature, a multi-pSMMU setup
will have multiple viommus (with our latest design) being added
to a viommu list of a single vSMMU's. Yet, vSMMU in this case
always traps regular SMMU CMDQ, so it can do viommu selection
or even broadcast (if it has to).
Thanks
Nicolin
next prev parent reply other threads:[~2024-05-24 5:40 UTC|newest]
Thread overview: 118+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-13 3:46 [PATCH RFCv1 00/14] Add Tegra241 (Grace) CMDQV Support (part 2/2) Nicolin Chen
2024-04-13 3:46 ` [PATCH RFCv1 01/14] iommufd: Move iommufd_object to public iommufd header Nicolin Chen
2024-05-12 13:21 ` Jason Gunthorpe
2024-05-12 22:40 ` Nicolin Chen
2024-05-13 22:30 ` Jason Gunthorpe
2024-04-13 3:46 ` [PATCH RFCv1 02/14] iommufd: Swap _iommufd_object_alloc and __iommufd_object_alloc Nicolin Chen
2024-05-12 13:26 ` Jason Gunthorpe
2024-05-13 2:29 ` Nicolin Chen
2024-05-13 3:44 ` Nicolin Chen
2024-05-13 22:30 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 03/14] iommufd: Prepare for viommu structures and functions Nicolin Chen
2024-05-12 13:42 ` Jason Gunthorpe
2024-05-13 2:35 ` Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 04/14] iommufd: Add struct iommufd_viommu and iommufd_viommu_ops Nicolin Chen
2024-05-12 14:03 ` Jason Gunthorpe
2024-05-13 3:34 ` Nicolin Chen
2024-05-14 15:55 ` Jason Gunthorpe
2024-05-22 8:58 ` Tian, Kevin
2024-05-22 9:57 ` Baolu Lu
2024-05-22 13:39 ` Jason Gunthorpe
2024-05-23 1:43 ` Tian, Kevin
2024-05-23 4:01 ` Nicolin Chen
2024-05-23 5:40 ` Tian, Kevin
2024-05-23 12:58 ` Jason Gunthorpe
2024-05-24 2:16 ` Tian, Kevin
2024-05-24 13:03 ` Jason Gunthorpe
2024-05-24 2:36 ` Tian, Kevin
2024-04-13 3:47 ` [PATCH RFCv1 05/14] iommufd: Add IOMMUFD_OBJ_VIOMMU and IOMMUFD_CMD_VIOMMU_ALLOC Nicolin Chen
2024-05-12 14:27 ` Jason Gunthorpe
2024-05-13 4:33 ` Nicolin Chen
2024-05-14 15:38 ` Jason Gunthorpe
2024-05-15 1:20 ` Nicolin Chen
2024-05-21 18:05 ` Jason Gunthorpe
2024-05-22 0:13 ` Nicolin Chen
2024-05-22 16:46 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 06/14] iommufd/selftest: Add IOMMU_VIOMMU_ALLOC test coverage Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 07/14] iommufd: Add viommu set/unset_dev_id ops Nicolin Chen
2024-05-12 14:46 ` Jason Gunthorpe
2024-05-13 4:39 ` Nicolin Chen
2024-05-14 15:53 ` Jason Gunthorpe
2024-05-15 1:59 ` Nicolin Chen
2024-05-21 18:24 ` Jason Gunthorpe
2024-05-21 22:27 ` Nicolin Chen
2024-05-22 13:59 ` Jason Gunthorpe
2024-05-23 6:19 ` Tian, Kevin
2024-05-23 15:01 ` Jason Gunthorpe
2024-05-24 2:21 ` Tian, Kevin
2024-05-24 3:26 ` Nicolin Chen
2024-05-24 5:24 ` Tian, Kevin
2024-05-24 5:57 ` Nicolin Chen
2024-05-24 7:21 ` Tian, Kevin
2024-05-24 13:12 ` Jason Gunthorpe
2024-05-24 13:05 ` Jason Gunthorpe
2024-05-23 5:44 ` Tian, Kevin
2024-05-23 6:09 ` Nicolin Chen
2024-05-23 6:22 ` Tian, Kevin
2024-05-23 13:33 ` Jason Gunthorpe
2024-05-12 14:51 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl Nicolin Chen
2024-05-12 14:58 ` Jason Gunthorpe
2024-05-13 5:24 ` Nicolin Chen
2024-05-17 5:14 ` Nicolin Chen
2024-05-21 18:30 ` Jason Gunthorpe
2024-05-22 2:15 ` Nicolin Chen
2024-05-23 6:42 ` Tian, Kevin
2024-05-24 5:40 ` Nicolin Chen [this message]
2024-05-24 7:13 ` Tian, Kevin
2024-05-24 13:19 ` Jason Gunthorpe
2024-05-27 1:08 ` Tian, Kevin
2024-05-28 20:22 ` Nicolin Chen
2024-05-28 20:33 ` Nicolin Chen
2024-05-29 2:58 ` Tian, Kevin
2024-05-29 3:20 ` Nicolin Chen
2024-05-30 0:28 ` Tian, Kevin
2024-05-30 0:58 ` Nicolin Chen
2024-05-30 3:05 ` Tian, Kevin
2024-05-30 4:26 ` Nicolin Chen
2024-06-01 21:45 ` Jason Gunthorpe
2024-06-03 3:25 ` Nicolin Chen
2024-06-06 18:24 ` Jason Gunthorpe
2024-06-06 18:44 ` Nicolin Chen
2024-06-07 0:27 ` Jason Gunthorpe
2024-06-07 0:36 ` Tian, Kevin
2024-06-07 14:49 ` Jason Gunthorpe
2024-06-07 21:19 ` Nicolin Chen
2024-06-10 12:04 ` Jason Gunthorpe
2024-06-10 20:01 ` Nicolin Chen
2024-06-10 22:01 ` Jason Gunthorpe
2024-06-10 23:04 ` Nicolin Chen
2024-06-11 0:28 ` Jason Gunthorpe
2024-06-11 0:44 ` Nicolin Chen
2024-06-11 12:17 ` Jason Gunthorpe
2024-06-11 19:11 ` Nicolin Chen
2024-05-28 20:30 ` Nicolin Chen
2024-05-24 13:20 ` Jason Gunthorpe
2024-04-13 3:47 ` [PATCH RFCv1 09/14] iommufd/selftest: Add IOMMU_VIOMMU_SET_DEV_ID test coverage Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 10/14] iommufd/selftest: Add IOMMU_TEST_OP_MV_CHECK_DEV_ID Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 11/14] iommufd: Add struct iommufd_vqueue and its related viommu ops Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 12/14] iommufd: Add IOMMUFD_OBJ_VQUEUE and IOMMUFD_CMD_VQUEUE_ALLOC Nicolin Chen
2024-05-12 15:02 ` Jason Gunthorpe
2024-05-13 4:41 ` Nicolin Chen
2024-05-13 22:36 ` Jason Gunthorpe
2024-05-23 6:57 ` Tian, Kevin
2024-05-24 4:42 ` Nicolin Chen
2024-05-24 5:26 ` Tian, Kevin
2024-05-24 6:03 ` Nicolin Chen
2024-05-23 7:05 ` Tian, Kevin
2024-04-13 3:47 ` [PATCH RFCv1 13/14] iommufd: Add mmap infrastructure Nicolin Chen
2024-05-12 15:19 ` Jason Gunthorpe
2024-05-13 4:43 ` Nicolin Chen
2024-04-13 3:47 ` [PATCH RFCv1 14/14] iommu/tegra241-cmdqv: Add user-space use support Nicolin Chen
2024-05-22 8:40 ` [PATCH RFCv1 00/14] Add Tegra241 (Grace) CMDQV Support (part 2/2) Tian, Kevin
2024-05-22 16:48 ` Jason Gunthorpe
2024-05-22 19:47 ` Nicolin Chen
2024-05-22 23:28 ` Jason Gunthorpe
2024-05-22 23:43 ` Tian, Kevin
2024-05-23 3:09 ` Nicolin Chen
2024-05-23 12:48 ` Jason Gunthorpe
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=ZlAoN3s96HL7ROth@nvidia.com \
--to=nicolinc@nvidia.com \
--cc=Dhaval.Giani@amd.com \
--cc=eric.auger@redhat.com \
--cc=iommu@lists.linux.dev \
--cc=jgg@nvidia.com \
--cc=jon.grimm@amd.com \
--cc=joro@8bytes.org \
--cc=kevin.tian@intel.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tegra@vger.kernel.org \
--cc=robin.murphy@arm.com \
--cc=santosh.shukla@amd.com \
--cc=shameerali.kolothum.thodi@huawei.com \
--cc=suravee.suthikulpanit@amd.com \
--cc=vasant.hegde@amd.com \
--cc=will@kernel.org \
--cc=yi.l.liu@intel.com \
/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 read-only IMAP folder(s) and NNTP newsgroup(s).