linux-kernel - Re: [PATCH v3 05/17] kexec: Add KHO support to kexec file loads

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Message-ID: <mafs0le7k8lo2.fsf@amazon.de>
Date: Fri, 16 Feb 2024 16:37:49 +0100
From: Pratyush Yadav <ptyadav@...zon.de>
To: Alexander Graf <graf@...zon.com>
CC: <linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <kexec@...ts.infradead.org>,
	<linux-doc@...r.kernel.org>, <x86@...nel.org>, Eric Biederman
	<ebiederm@...ssion.com>, "H . Peter Anvin" <hpa@...or.com>, Andy Lutomirski
	<luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt
	<rostedt@...dmis.org>, Andrew Morton <akpm@...ux-foundation.org>, "Mark
 Rutland" <mark.rutland@....com>, Tom Lendacky <thomas.lendacky@....com>,
	Ashish Kalra <ashish.kalra@....com>, James Gowans <jgowans@...zon.com>,
	Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>, <arnd@...db.de>,
	<pbonzini@...hat.com>, <madvenka@...ux.microsoft.com>, Anthony Yznaga
	<anthony.yznaga@...cle.com>, Usama Arif <usama.arif@...edance.com>, "David
 Woodhouse" <dwmw@...zon.co.uk>, Benjamin Herrenschmidt
	<benh@...nel.crashing.org>, Rob Herring <robh+dt@...nel.org>, "Krzysztof
 Kozlowski" <krzk@...nel.org>
Subject: Re: [PATCH v3 05/17] kexec: Add KHO support to kexec file loads

Hi,

On Wed, Jan 17 2024, Alexander Graf wrote:

> Kexec has 2 modes: A user space driven mode and a kernel driven mode.
> For the kernel driven mode, kernel code determines the physical
> addresses of all target buffers that the payload gets copied into.
>
> With KHO, we can only safely copy payloads into the "scratch area".
> Teach the kexec file loader about it, so it only allocates for that
> area. In addition, enlighten it with support to ask the KHO subsystem
> for its respective payloads to copy into target memory. Also teach the
> KHO subsystem how to fill the images for file loads.

This patch causes compilation failures when CONFIG_KEXEC_FILE is not
enabled. I am not listing them all here since there are a bunch. You can
try disabling it and see them for yourself.

Since Documentation/kho/usage.rst says:

    It is important that you use the ``-s`` parameter to use the
    in-kernel kexec file loader, as user space kexec tooling currently
    has no support for KHO with the user space based file loader.

you can just make CONFIG_KEXEC_FILE a dependency for CONFIG_KEXEC_KHO to
get rid of these errors.

Or, if you foresee wanting to use the user space tooling to use KHO as
well then you should refactor your code to work with the option enabled
and disabled.

>
> Signed-off-by: Alexander Graf <graf@...zon.com>
[...]

--
Regards,
Pratyush Yadav



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