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

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Message-ID: <BN9PR11MB5276907FC927424043C636E68C9FA@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Fri, 30 Jan 2026 03:12:02 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jason Gunthorpe <jgg@...pe.ca>
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Subject: RE: [PATCH v5 4/8] vfio: Wait for dma-buf invalidation to complete

> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Thursday, January 29, 2026 10:59 PM
> 
> 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.

good to know those background.

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

either way is OK. It's not difficult to figure out a long wait anyway. 😊