linux-kernel - Re: [PATCH] arm64: kdump: Fix elfcorehdr overlap caused by reserved memory processing reorder

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Message-ID: <20251208170825.GA2056564-robh@kernel.org>
Date: Mon, 8 Dec 2025 11:08:25 -0600
From: Rob Herring <robh@...nel.org>
To: Jianpeng Chang <jianpeng.chang.cn@...driver.com>
Cc: saravanak@...gle.com, quic_obabatun@...cinc.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: kdump: Fix elfcorehdr overlap caused by reserved
 memory processing reorder

On Fri, Dec 05, 2025 at 09:59:34AM +0800, Jianpeng Chang wrote:
> Commit 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved
> memory regions are processed") changed the processing order of reserved
> memory regions, causing elfcorehdr to overlap with dynamically allocated
> reserved memory regions during kdump kernel boot.
> 
> The issue occurs because:
> 1. kexec-tools allocates elfcorehdr in the last crashkernel reserved
>    memory region and passes it to the second kernel
> 2. The problematic commit moved dynamic reserved memory allocation
>    (like bman-fbpr) to occur during fdt_scan_reserved_mem(), before
>    elfcorehdr reservation in fdt_reserve_elfcorehdr()
> 3. bman-fbpr with 16MB alignment requirement can get allocated at
>    addresses that overlap with the elfcorehdr location
> 4. When fdt_reserve_elfcorehdr() tries to reserve elfcorehdr memory,
>    overlap detection identifies the conflict and skips reservation
> 5. kdump kernel fails with "Unable to handle kernel paging request"
>    because elfcorehdr memory is not properly reserved
> 
> The boot log:
> Before 8a6e02d0c00e:
>   OF: fdt: Reserving 1 KiB of memory at 0xf4fff000 for elfcorehdr
>   OF: reserved mem: 0xf3000000..0xf3ffffff bman-fbpr
> 
> After 8a6e02d0c00e:
>   OF: reserved mem: 0xf4000000..0xf4ffffff bman-fbpr
>   OF: fdt: elfcorehdr is overlapped
> 
> Fix this by ensuring elfcorehdr reservation occurs before dynamic
> reserved memory allocation.
> 
> Fixes: 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved memory regions are processed")
> Signed-off-by: Jianpeng Chang <jianpeng.chang.cn@...driver.com>
> ---
> This BUG is manifested on NXP LS1043 platforms, while other
> platforms don't trigger this issue, it represents a general problem,
> and it's more safer to follow original reservation order.
> 
>  drivers/of/fdt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thanks.

Rob