linux-kernel - Re: [PATCH v4 05/14] kexec: Add Kexec HandOver (KHO) generation helpers

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] [day] [month] [year] [list]

Message-ID: <20250211163720.GH3754072@nvidia.com>
Date: Tue, 11 Feb 2025 12:37:20 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
	Alexander Graf <graf@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Anthony Yznaga <anthony.yznaga@...cle.com>,
	Arnd Bergmann <arnd@...db.de>, Ashish Kalra <ashish.kalra@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Borislav Petkov <bp@...en8.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Eric Biederman <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...hat.com>, James Gowans <jgowans@...zon.com>,
	Jonathan Corbet <corbet@....net>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pratyush Yadav <ptyadav@...zon.de>,
	Rob Herring <robh+dt@...nel.org>, Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Lendacky <thomas.lendacky@....com>,
	Usama Arif <usama.arif@...edance.com>,
	Will Deacon <will@...nel.org>, devicetree@...r.kernel.org,
	kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH v4 05/14] kexec: Add Kexec HandOver (KHO) generation
 helpers

On Tue, Feb 11, 2025 at 11:14:06AM -0500, Pasha Tatashin wrote:
> > think you should not add this when there are enough ideas on how to
> > completely avoid it.
> 
> Thinking about it some more, I'm actually leaning towards keeping
> things as they are, instead of going with a sparse FDT. 

What is a sparse FDT? My suggestion each driver make its own FDT?

The reason for this was sequencing because we need a more more
flexable way to manage all this serialization than just a notifier
chain. The existing FDT construction process is too restrictive to
accommodate this, IMHO.

That it also resolves the weird dt_max stuff above is a nice side
effect.

> With a sparse KHO-tree, we'd be kinda trying to fix something that
> should be handled higher up. All userspace preservable memory (like
> emulated pmem with devdax/fsdax and also pstore for logging) can
> already survive cold reboots with modified firmware Google and
> Microsoft do this.

I was hoping the VM memory wouldn't be in DAX. If you want some DAX
stuff to interact with FW, OK, but I think the design here should be
driving toward preserving a memfd/guestmemfd/hugetlbfs FDs directly
and eliminate the DAX backed VMs. We won't get to CC guestmemfd with
DAX.

fdbox of a guestmemfd, for instance.

To do that you need to preserve folios as the basic primitive.

> Similarly, the firmware could give the kernel the KHO-tree (generated
> by firmware or from the previous kernel) to keep stuff like telemetry,
> oops messages, time stamps etc. 

This feels like a mistake to comingle things like this. KHO is complex
enough, it should stay focused on its thing..

Jason