linux-kernel - Re: [PATCH v2 1/1] kexec_core: Accept unaccepted kexec segments' destination addresses

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Message-ID: <69dc7277-7aa8-4091-8993-ff1195ef4c3a@intel.com>
Date: Thu, 13 Feb 2025 07:50:42 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Yan Zhao <yan.y.zhao@...el.com>, ebiederm@...ssion.com
Cc: kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-coco@...ts.linux.dev, x86@...nel.org, rick.p.edgecombe@...el.com,
 kirill.shutemov@...ux.intel.com, bhe@...hat.com
Subject: Re: [PATCH v2 1/1] kexec_core: Accept unaccepted kexec segments'
 destination addresses

On 12/13/24 01:54, Yan Zhao wrote:
> +	/*
> +	 * The destination addresses are searched from system RAM rather than
> +	 * being allocated from the buddy allocator, so they are not guaranteed
> +	 * to be accepted by the current kernel.  Accept the destination
> +	 * addresses before kexec swaps their content with the segments' source
> +	 * pages to avoid accessing memory before it is accepted.
> +	 */
> +	for (i = 0; i < nr_segments; i++)
> +		accept_memory(image->segment[i].mem, image->segment[i].memsz);

The "searched from system RAM" phrase both here and in the changelog
doesn't quite parse for me.

Also "System RAM" is the normal phrase that I use to describe the memory
that mostly ends up _going_ into the buddy allocator. It's not just me:

	cat /proc/iomem  | grep 'System RAM'

I think a more useful comment (and changelog) might be something like this:

	The core kernel focuses on accepting memory which is known to be
	System RAM. However, there might be areas that are reserved in
	the memory map, not exposed to the kernel as "System RAM" and
	not accepted by firmware. Accept the memory before kexec touches
	it.