linux-kernel - Re: [PATCH v4 04/40] drm/sched: Add enqueue credit limit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAF6AEGsoG_W3A3+BHV4n5EKZQazFubrCyfrtxVUH7+H4-j7i5A@mail.gmail.com>
Date: Thu, 15 May 2025 10:40:15 -0700
From: Rob Clark <robdclark@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Connor Abbott <cwabbott0@...il.com>, Rob Clark <robdclark@...omium.org>, phasta@...nel.org, 
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org, 
	linux-arm-msm@...r.kernel.org, Matthew Brost <matthew.brost@...el.com>, 
	Christian König <ckoenig.leichtzumerken@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	open list <linux-kernel@...r.kernel.org>, 
	Boris Brezillon <boris.brezillon@...labora.com>
Subject: Re: [PATCH v4 04/40] drm/sched: Add enqueue credit limit

On Thu, May 15, 2025 at 10:30 AM Danilo Krummrich <dakr@...nel.org> wrote:
>
> (Cc: Boris)
>
> On Thu, May 15, 2025 at 12:22:18PM -0400, Connor Abbott wrote:
> > For some context, other drivers have the concept of a "synchronous"
> > VM_BIND ioctl which completes immediately, and drivers implement it by
> > waiting for the whole thing to finish before returning.
>
> Nouveau implements sync by issuing a normal async VM_BIND and subsequently
> waits for the out-fence synchronously.

As Connor mentioned, we'd prefer it to be async rather than blocking,
in normal cases, otherwise with drm native context for using native
UMD in guest VM, you'd be blocking the single host/VMM virglrender
thread.

The key is we want to keep it async in the normal cases, and not have
weird edge case CTS tests blow up from being _too_ async ;-)

> > But this
> > doesn't work for native context, where everything has to be
> > asynchronous, so we're trying a new approach where we instead submit
> > an asynchronous bind for "normal" (non-sparse/driver internal)
> > allocations and only attach its out-fence to the in-fence of
> > subsequent submits to other queues.
>
> This is what nouveau does and I think other drivers like Xe and panthor do this
> as well.

No one has added native context support for these drivers yet

> > Once you do this then you need a
> > limit like this to prevent memory usage from pending page table
> > updates from getting out of control. Other drivers haven't needed this
> > yet, but they will when they get native context support.
>
> What are the cases where you did run into this, i.e. which application in
> userspace hit this? Was it the CTS, some game, something else?

CTS tests that do weird things with massive # of small bind/unbind.  I
wouldn't expect to hit the blocking case in the real world.

BR,
-R