linux-kernel - Re: [RFC PATCH 1/4] efi/libstub: Decouple memory bitmap from the unaccepted table

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Message-ID: <phywn74ghpsqncoqsgdqjoxeqdxskibzt3yltn6bmtc25sm46g@emad5n6wp5l2>
Date: Wed, 26 Nov 2025 11:08:05 +0000
From: Kiryl Shutsemau <kas@...nel.org>
To: "Pratik R. Sampat" <prsampat@....com>
Cc: linux-mm@...ck.org, linux-coco@...ts.linux.dev, 
	linux-efi@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, ardb@...nel.org, 
	akpm@...ux-foundation.org, david@...hat.com, osalvador@...e.de, thomas.lendacky@....com, 
	michael.roth@....com
Subject: Re: [RFC PATCH 1/4] efi/libstub: Decouple memory bitmap from the
 unaccepted table

On Tue, Nov 25, 2025 at 11:57:50AM -0600, Pratik R. Sampat wrote:
> Memory hotplug in secure environments requires the unaccepted memory
> bitmap to grow as new memory is added. Currently, the bitmap is
> implemented as a flexible array member at the end of struct
> efi_unaccepted_memory, which is reserved by memblock at boot and cannot
> be resized without reallocating the entire structure.
> 
> Replace the flexible array member with a pointer.

Well, it break interoperability between kernel before and after the
patch. Consider kexec from kernel without the patch to the kernel with
the patch and then back to older kernel. It is ABI break.

Is re-allocating the entire structure such a big pain?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov