linux-kernel - Re: [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in non-coherent domains

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Date: Wed, 22 May 2024 11:24:20 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Alex Williamson <alex.williamson@...hat.com>, "Tian, Kevin"
	<kevin.tian@...el.com>, "Vetter, Daniel" <daniel.vetter@...el.com>,
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	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, "pbonzini@...hat.com"
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	"robin.murphy@....com" <robin.murphy@....com>, "baolu.lu@...ux.intel.com"
	<baolu.lu@...ux.intel.com>, "Liu, Yi L" <yi.l.liu@...el.com>
Subject: Re: [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in
 non-coherent domains

On Tue, May 21, 2024 at 01:34:00PM -0300, Jason Gunthorpe wrote:
> On Tue, May 21, 2024 at 10:21:23AM -0600, Alex Williamson wrote:
> 
> > > Intel GPU weirdness should not leak into making other devices
> > > insecure/slow. If necessary Intel GPU only should get some variant
> > > override to keep no snoop working.
> > > 
> > > It would make alot of good sense if VFIO made the default to disable
> > > no-snoop via the config space.
> > 
> > We can certainly virtualize the config space no-snoop enable bit, but
> > I'm not sure what it actually accomplishes.  We'd then be relying on
> > the device to honor the bit and not have any backdoors to twiddle the
> > bit otherwise (where we know that GPUs often have multiple paths to get
> > to config space).
> 
> I'm OK with this. If devices are insecure then they need quirks in
> vfio to disclose their problems, we shouldn't punish everyone who
> followed the spec because of some bad actors.
Does that mean a malicous device that does not honor the bit could read
uninitialized host data?