From: Jason Gunthorpe <jgg@nvidia.com>
To: Nicolin Chen <nicolinc@nvidia.com>
Cc: kevin.tian@intel.com, yi.l.liu@intel.com, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] iommufd: Add devices_users to track the hw_pagetable usage by device
Date: Mon, 30 Jan 2023 15:50:07 -0400 [thread overview]
Message-ID: <Y9gfbx/fszb0aTJn@nvidia.com> (raw)
In-Reply-To: <Y9gaKaMKOf+P2NtK@Asurada-Nvidia>
On Mon, Jan 30, 2023 at 11:27:37AM -0800, Nicolin Chen wrote:
> On Mon, Jan 30, 2023 at 11:02:25AM -0400, Jason Gunthorpe wrote:
> > On Sat, Jan 28, 2023 at 01:18:09PM -0800, Nicolin Chen wrote:
> > > From: Yi Liu <yi.l.liu@intel.com>
> > >
> > > Currently, hw_pagetable tracks the attached devices using a device list.
> > > When attaching the first device to the kernel-managed hw_pagetable, it
> > > should be linked to IOAS. When detaching the last device from this hwpt,
> > > the link with IOAS should be removed too. And this first-or-last device
> > > check is done with list_empty(hwpt->devices).
> > >
> > > However, with a nested configuration, when a device is attached to the
> > > user-managed stage-1 hw_pagetable, it will be added to this user-managed
> > > hwpt's device list instead of the kernel-managed stage-2 hwpt's one. And
> > > this breaks the logic for a kernel-managed hw_pagetable link/disconnect
> > > to/from IOAS/IOPT. e.g. the stage-2 hw_pagetable would be linked to IOAS
> > > multiple times if multiple device is attached, but it will become empty
> > > as soon as one device detached.
> >
> > Why this seems really weird to say.
> >
> > The stage 2 is linked explicitly to the IOAS that drives it's
> > map/unmap
> >
> > Why is there any implicit activity here? There should be no implicit
> > attach of the S2 to an IOAS ever.
>
> I think this is supposed to say the following use case:
>
> Two stage-1 hwpts share the same parent s2_hwpt:
>
> attach device1 to stage-1 hwpt1:
> ...
> if (list_empty(s1_hwpt1->devices)) // empty; true
> iopt_table_add_domain(s2_hwpt->domain); // do once
> s1_hwpt1 device list cnt++;
> ...
No, this doesn't make sense.
The s2_hwpt should be created explicitly, not using autodomains
When it is created it should be linked to a single IOAS and that is
when iopt_table_add_domain() should have been called.
The S1 attach should do *nothing* to a S2.
Jason
next prev parent reply other threads:[~2023-01-30 19:50 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-28 21:18 [PATCH v2 0/3] iommufd: Remove iommufd_hw_pagetable_has_group Nicolin Chen
2023-01-28 21:18 ` [PATCH v2 1/3] iommufd: Add devices_users to track the hw_pagetable usage by device Nicolin Chen
2023-01-29 9:23 ` Tian, Kevin
2023-01-29 9:30 ` Nicolin Chen
2023-01-29 9:39 ` Tian, Kevin
2023-01-30 2:22 ` Liu, Yi L
2023-01-30 15:02 ` Jason Gunthorpe
2023-01-30 19:27 ` Nicolin Chen
2023-01-30 19:50 ` Jason Gunthorpe [this message]
2023-01-30 20:04 ` Nicolin Chen
2023-01-30 20:35 ` Jason Gunthorpe
2023-01-30 20:53 ` Nicolin Chen
2023-02-01 7:48 ` Nicolin Chen
2023-02-02 9:12 ` Nicolin Chen
2023-02-07 4:19 ` Liu, Yi L
2023-02-01 6:57 ` Nicolin Chen
2023-02-01 7:56 ` Nicolin Chen
2023-02-01 15:53 ` Jason Gunthorpe
2023-02-01 17:46 ` Nicolin Chen
2023-02-01 18:37 ` Jason Gunthorpe
2023-02-01 19:25 ` Nicolin Chen
2023-02-01 20:00 ` Jason Gunthorpe
2023-02-01 21:18 ` Nicolin Chen
2023-02-02 7:28 ` Nicolin Chen
2023-02-02 15:03 ` Jason Gunthorpe
2023-02-07 4:27 ` Liu, Yi L
2023-01-28 21:18 ` [PATCH v2 2/3] iommufd/device: Make hwpt_list list_add/del symmetric Nicolin Chen
2023-01-29 9:24 ` Tian, Kevin
2023-01-29 9:31 ` Nicolin Chen
2023-01-30 14:59 ` Jason Gunthorpe
2023-01-30 19:03 ` Nicolin Chen
2023-01-30 19:07 ` Jason Gunthorpe
2023-01-30 19:38 ` Nicolin Chen
2023-01-28 21:18 ` [PATCH v2 3/3] iommufd/device: Change iommufd_hw_pagetable_has_group to device centric Nicolin Chen
2023-01-29 9:37 ` Tian, Kevin
2023-01-29 10:38 ` Nicolin Chen
2023-01-30 0:44 ` Tian, Kevin
2023-01-30 10:22 ` Nicolin Chen
2023-02-01 3:07 ` Tian, Kevin
2023-02-01 6:49 ` Baolu Lu
2023-02-01 6:59 ` Tian, Kevin
2023-02-01 7:20 ` Nicolin Chen
2023-02-02 6:32 ` Tian, Kevin
2023-02-02 6:36 ` Nicolin Chen
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=Y9gfbx/fszb0aTJn@nvidia.com \
--to=jgg@nvidia.com \
--cc=iommu@lists.linux.dev \
--cc=kevin.tian@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=nicolinc@nvidia.com \
--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 NNTP newsgroup(s).