linux-kernel - Re: [RFC PATCH 26/39] KVM: guest_memfd: Track faultability within a struct kvm_gmem

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Message-ID: <ZxBRC-v9w7xS0xgk@x1n>
Date: Wed, 16 Oct 2024 19:49:31 -0400
From: Peter Xu <peterx@...hat.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: David Hildenbrand <david@...hat.com>,
	Ackerley Tng <ackerleytng@...gle.com>, tabba@...gle.com,
	quic_eberman@...cinc.com, roypat@...zon.co.uk, rientjes@...gle.com,
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	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH 26/39] KVM: guest_memfd: Track faultability within a
 struct kvm_gmem_private

On Wed, Oct 16, 2024 at 07:51:57PM -0300, Jason Gunthorpe wrote:
> On Wed, Oct 16, 2024 at 04:16:17PM -0400, Peter Xu wrote:
> > 
> > Is there chance that when !CoCo will be supported, then external modules
> > (e.g. VFIO) can reuse the old user mappings, just like before gmemfd?
> > 
> > To support CoCo, I understand gmem+offset is required all over the places.
> > However in a non-CoCo context, I wonder whether the other modules are
> > required to stick with gmem+offset, or they can reuse the old VA ways,
> > because how it works can fundamentally be the same as before, except that
> > the folios now will be managed by gmemfd.
> 
> My intention with iommufd was to see fd + offest as the "new" way
> to refer to all guest memory and discourage people from using VMA
> handles.

Does it mean anonymous memory guests will not be supported at all for
iommufd?

Indeed it's very rare now, lose quite some flexibility (v.s. fd based), and
I can't think of a lot besides some default configs or KSM users (which I
would expect rare), but still I wonder there're other use cases that people
would still need to stick with anon, hence fd isn't around.

Thanks,

-- 
Peter Xu