linux-kernel - Re: [PATCH 00/21] mm: ASI direct map management

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Message-ID: <CA+i-1C3ry07NdPFFS3m2-WoboffgPSrOASJ4pPvoF=cN8NxbBg@mail.gmail.com>
Date: Wed, 1 Oct 2025 09:12:25 +0200
From: Brendan Jackman <jackmanb@...gle.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Andy Lutomirski <luto@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>, 
	Axel Rasmussen <axelrasmussen@...gle.com>, Yuanchu Xie <yuanchu@...gle.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, peterz@...radead.org, bp@...en8.de, 
	dave.hansen@...ux.intel.com, mingo@...hat.com, tglx@...utronix.de, 
	akpm@...ux-foundation.org, david@...hat.com, derkling@...gle.com, 
	junaids@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	reijiw@...gle.com, rientjes@...gle.com, rppt@...nel.org, vbabka@...e.cz, 
	x86@...nel.org, Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH 00/21] mm: ASI direct map management

On Tue, 30 Sept 2025 at 21:51, Konrad Rzeszutek Wilk
<konrad.wilk@...cle.com> wrote:
>
> On Wed, Sep 24, 2025 at 02:59:35PM +0000, Brendan Jackman wrote:
> > As per [0] I think ASI is ready to start merging. This is the first
> > step. The scope of this series is: everything needed to set up the
> > direct map in the restricted address spaces.
>
> There looks to be a different approach taken by other folks to
> yank the guest pages from the hypervisor:
>
> https://lore.kernel.org/kvm/20250912091708.17502-1-roypat@amazon.co.uk/
>
> That looks to have a very similar end result with less changes?

Hey Konrad,

Yeah if you only care about the security boundary around VM guests,
and you're able to rework your hypervisor stack appropriately (I don't
know too much about this but presumably it's just a subset of what's
needed to support confidential computing usecases?), that approach
seems good to me.

But that isn't true for most of Linux's users. We still need to
support systems where there is a meaningful security boundary around
native processes. Also, unless I'm mistaken Patrick's approach will
always require changes to the VMM, I don't think the kernel can just
tell all users to go and make those changes.

Basically: I support that approach, it's a good idea. It just solves a
different set of problems. (I haven't thought about it carefully but I
guess it solves some problems that ASI doesn't, since I guess it
prevents some set of software exploits too, while ASI only helps with
HW vulns).

Cheers,
Brendan