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

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: <20241017171010.GK3559746@nvidia.com>
Date: Thu, 17 Oct 2024 14:10:10 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Peter Xu <peterx@...hat.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,
	fvdl@...gle.com, jthoughton@...gle.com, seanjc@...gle.com,
	pbonzini@...hat.com, zhiquan1.li@...el.com, fan.du@...el.com,
	jun.miao@...el.com, isaku.yamahata@...el.com, muchun.song@...ux.dev,
	erdemaktas@...gle.com, vannapurve@...gle.com, qperret@...gle.com,
	jhubbard@...dia.com, willy@...radead.org, shuah@...nel.org,
	brauner@...nel.org, bfoster@...hat.com, kent.overstreet@...ux.dev,
	pvorel@...e.cz, rppt@...nel.org, richard.weiyang@...il.com,
	anup@...infault.org, haibo1.xu@...el.com, ajones@...tanamicro.com,
	vkuznets@...hat.com, maciej.wieczor-retman@...el.com,
	pgonda@...gle.com, oliver.upton@...ux.dev,
	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 Thu, Oct 17, 2024 at 01:05:34PM -0400, Peter Xu wrote:
> On Thu, Oct 17, 2024 at 01:47:13PM -0300, Jason Gunthorpe wrote:
> > On Thu, Oct 17, 2024 at 10:58:29AM -0400, Peter Xu wrote:
> > 
> > > My question was more torwards whether gmemfd could still expose the
> > > possibility to be used in VA forms to other modules that may not support
> > > fd+offsets yet.
> > 
> > I keep hearing they don't want to support page pinning on a guestmemfd
> > mapping, so VA based paths could not work.
> 
> Do you remember the reasoning of it?  Is it because CoCo still needs to
> have a bounded time window to convert from shared back to private?  

I think so

> If so, maybe that's a non-issue for non-CoCo, where the VM object /
> gmemfd object (when created) can have a flag marking that it's
> always shared and can never be converted to private for any page
> within.

What is non-CoCo? Does it include the private/shared concept?

> So how would VFIO's DMA work even with iommufd if pages cannot be pinned?
> Is some form of bounce buffering required, then?

We can do some kind of atomic replace during a private/shared
exchange. In some HW cases the iommu table doesn't even need an
update.

It will be tricky stuff.

Jason