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

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Message-ID: <mafs0qzuvfd2z.fsf@kernel.org>
Date: Wed, 22 Oct 2025 12:25:08 +0200
From: Pratyush Yadav <pratyush@...nel.org>
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,  dmatlack@...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, Pasha Tatashin 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.
>
> The kfence specifically may cause memory corruption, where it randomly
> provides slab objects that can be within the scratch area. The reason
> for that is that kfence allocates its objects prior to KHO scratch is
> marked as CMA region.
>
> While this change could potentially increase metadata overhead on
> systems with sparsely preserved memory, this is being mitigated by
> ongoing work to reduce sparseness during preservation via 1G guest
> pages. Furthermore, this change aligns with future work on a stateless
> KHO, which will also use page-sized bitmaps for its radix tree metadata.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>

Reviewed-by: Pratyush Yadav <pratyush@...nel.org>

[...]

-- 
Regards,
Pratyush Yadav