linux-kernel - Re: [PATCH v4 00/14] kexec: introduce Kexec HandOver (KHO)

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Message-ID: <CA+CK2bDgP2DfsfVAhQhFhBiNJFUS1n17oX9KgC1JFXAk76j01Q@mail.gmail.com>
Date: Sat, 8 Feb 2025 19:23:25 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Baoquan He <bhe@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Mike Rapoport <rppt@...nel.org>, 
	linux-kernel@...r.kernel.org, Alexander Graf <graf@...zon.com>, 
	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, 
	changyuanl@...gle.com
Subject: Re: [PATCH v4 00/14] kexec: introduce Kexec HandOver (KHO)

On Fri, Feb 7, 2025 at 8:38 PM Baoquan He <bhe@...hat.com> wrote:
>
> On 02/06/25 at 08:28pm, Pasha Tatashin wrote:
> > On Thu, Feb 6, 2025 at 7:29 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> > >
> > > On Thu,  6 Feb 2025 15:27:40 +0200 Mike Rapoport <rppt@...nel.org> wrote:
> > >
> > > > This a next version of Alex's "kexec: Allow preservation of ftrace buffers"
> > > > series (https://lore.kernel.org/all/20240117144704.602-1-graf@amazon.com),
> > > > just to make things simpler instead of ftrace we decided to preserve
> > > > "reserve_mem" regions.
> > > >
> > > > The patches are also available in git:
> > > > https://git.kernel.org/rppt/h/kho/v4
> > > >
> > > >
> > > > Kexec today considers itself purely a boot loader: When we enter the new
> > > > kernel, any state the previous kernel left behind is irrelevant and the
> > > > new kernel reinitializes the system.
> > >
> > > I tossed this into mm.git for some testing and exposure.
> > >
> > > What merge path are you anticipating?
> > >
> > > Review activity seems pretty thin thus far?
> >
> > KHO is going to be discussed at the upcoming lsfmm, we are also
> > planning to send v5 of this patch series (discussed with Mike
> > Rapoport) in a couple of weeks. It will include enhancements needed
> > for the hypervisor live update scenario:
>
> So is this V4 still a RFC if v5 will be sent by plan? Should we hold the
> reviewing until v5? Or this series is a infrustructure building, v5 will
> add more details as you listed as below. I am a little confused.

We will modify the existing patches and send as v5 because some
interfaces are going to be changed*.

Otherwise, v5 will make KHO a lot more flexible as it will allow to
use the tree all the time while the system is running instead of only
once during the activation phase.

* Changing interfaces  is optional, but decision whether to change
will be discussed at Hypervisor Live Update on Feb 10th:
https://lore.kernel.org/all/26a4b7ca-93a6-30e2-923b-f551ced03d62@google.com/

>
> >
> > 1. Allow nodes to be added to the KHO tree at any time
> > 2. Remove "activate" (I will also send a live update framework that
> > provides the activate functionality).
> > 3. Allow serialization during shutdown.
> > 4. Decouple KHO from kexec_file_load(), as kexec_file_load() should
> > not be used during live update blackout time.
> > 5. Enable multithreaded serialization by using hash-table as an
> > intermediate step before conversion to FDT.
>