linux-kernel - Re: [RFC PATCH v3 00/10] Add support for shared PTEs across processes

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Message-ID: <CAG48ez33CQmWnQR13WvuP+eiX=MEXch2s6n2+Ck+zT5Tgi5fEg@mail.gmail.com>
Date: Wed, 16 Oct 2024 15:25:34 +0200
From: Jann Horn <jannh@...gle.com>
To: Anthony Yznaga <anthony.yznaga@...cle.com>
Cc: akpm@...ux-foundation.org, willy@...radead.org, markhemm@...glemail.com, 
	viro@...iv.linux.org.uk, david@...hat.com, khalid@...nel.org, 
	andreyknvl@...il.com, dave.hansen@...el.com, luto@...nel.org, 
	brauner@...nel.org, arnd@...db.de, ebiederm@...ssion.com, 
	catalin.marinas@....com, linux-arch@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhiramat@...nel.org, 
	rostedt@...dmis.org, vasily.averin@...ux.dev, xhao@...ux.alibaba.com, 
	pcc@...gle.com, neilb@...e.de, maz@...nel.org
Subject: Re: [RFC PATCH v3 00/10] Add support for shared PTEs across processes

On Wed, Oct 16, 2024 at 2:59 AM Anthony Yznaga
<anthony.yznaga@...cle.com> wrote:
> On 10/14/24 1:07 PM, Jann Horn wrote:
> > Second, there is a newer mode for IOMMUv2 stuff (using the
> > mmu_notifier_ops::invalidate_range callback), where the idea is that
> > you have secondary MMUs that share the normal page tables, and so you
> > basically send them invalidations at the same time you invalidate the
> > primary MMU for the process. I think that's the right fit for this
> > usecase; however, last I looked, this code was extremely broken (see
> > https://lore.kernel.org/lkml/CAG48ez2NQKVbv=yG_fq_jtZjf8Q=+Wy54FxcFrK_OujFg5BwSQ@mail.gmail.com/
> > for context). Unless that's changed in the meantime, I think someone
> > would have to fix that code before it can be relied on for new
> > usecases.
>
> Thank you for this background! Looks like there have since been some
> changes to the mmu notifiers, and the invalidate_range callback became
> arch_invalidate_secondary_tlbs. I'm currently looking into using it to
> flush all TLBs.

Ah, nice, that looks much better now. With the caveat that, from what
I can tell, the notifiers only work on x86/arm64/powerpc - I guess
maybe that infrastructure should be gated on a HAVE_... arch config
flag...