linux-kernel - Re: [PATCH v3 2/3] liveupdate: kho: Increase metadata bitmap size to PAGE

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Message-ID: <CALzav=cprjK-WutXYKii28e37R=F7jPZfA5_=_Qh4HH5p2Um=A@mail.gmail.com>
Date: Mon, 27 Oct 2025 15:44:19 -0700
From: David Matlack <dmatlack@...gle.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, corbet@....net, 
	graf@...zon.com, jgg@...pe.ca, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org, masahiroy@...nel.org, 
	ojeda@...nel.org, pratyush@...nel.org, rdunlap@...radead.org, rppt@...nel.org, 
	tj@...nel.org, jasonmiu@...gle.com, skhawaja@...gle.com
Subject: Re: [PATCH v3 2/3] liveupdate: kho: Increase metadata bitmap size to PAGE_SIZE

On Mon, Oct 20, 2025 at 5:09 PM Pasha Tatashin
<pasha.tatashin@...een.com> wrote:
>
> KHO memory preservation metadata is preserved in 512 byte chunks which
> requires their allocation from slab allocator. Slabs are not safe to be
> used with KHO because of kfence, and because partial slabs may lead
> leaks to the next kernel. Change the size to be PAGE_SIZE.

> -#define PRESERVE_BITS (512 * 8)
> +#define PRESERVE_BITS (PAGE_SIZE * 8)

nit: A comment somewhere (maybe here?) about the requirement that KHO
metadata are not stored on slabs would be helpful to avoid someone
"optimizing" this back to 512 in the future.