linux-kernel - Re: [PATCH v5 4/8] vfio: Wait for dma-buf invalidation to complete

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Message-ID: <20260129145851.GE2307128@ziepe.ca>
Date: Thu, 29 Jan 2026 10:58:51 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Leon Romanovsky <leon@...nel.org>,
	Pranjal Shrivastava <praan@...gle.com>,
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Subject: Re: [PATCH v5 4/8] vfio: Wait for dma-buf invalidation to complete

On Thu, Jan 29, 2026 at 07:06:37AM +0000, Tian, Kevin wrote:
> Bear me if it's an ignorant question.
> 
> The commit msg of patch6 says that VFIO doesn't tolerate unbounded
> wait, which is the reason behind the 2nd timeout wait here.

As far as I understand dmabuf design a fence wait should complete
eventually under kernel control, because these sleeps are
sprinkled all around the kernel today.

I suspect that is not actually true for every HW, probably something
like "shader programs can run forever technically".

We can argue if those cases should not report revocable either, but at
least this will work "correctly" even if it takes a huge amount of
time.

I wouldn't mind seeing a shorter timeout and print on the fence too
just in case.

Jason