linux-kernel - Re: [PATCH] MIPS: reserve the memblock right after the kernel

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Message-ID: <27310707-78d5-0f96-7048-749db4959a07@nokia.com>
Date:   Mon, 9 Nov 2020 12:08:03 +0100
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     Jiaxun Yang <jiaxun.yang@...goat.com>, linux-mips@...r.kernel.org,
        Paul Burton <paulburton@...nel.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] MIPS: reserve the memblock right after the kernel

Hi Thomas,

On 09/11/2020 11:34, Alexander Sverdlin wrote:
>>> Linux doesn't own the memory immediately after the kernel image. On Octeon
>>> bootloader places a shared structure right close after the kernel _end,
>>> refer to "struct cvmx_bootinfo *octeon_bootinfo" in cavium-octeon/setup.c.
>>>
>>> If check_kernel_sections_mem() rounds the PFNs up, first memblock_alloc()
>>> inside early_init_dt_alloc_memory_arch() <= device_tree_init() returns
>>> memory block overlapping with the above octeon_bootinfo structure, which
>>> is being overwritten afterwards.
>> as this special for Octeon how about added the memblock_reserve
>> in octen specific code ?
> while the shared structure which is being corrupted is indeed Octeon-specific,
> the wrong assumption that the memory right after the kernel can be allocated by memblock
> allocator and re-used somewhere in Linux is in MIPS-generic check_kernel_sections_mem().
> 
> I personally will be fine with repairing Octeon only as I don't have other MIPS
> targets to care about, but maybe someone else in the MIPS community will find
> this fix useful...

another reason for not putting that to Octeon platform code was the fact, that one
would need to put the knowledge about wrong assumption of ARCH (MIPS) code into
different code area of Octeon platform.
If at some point in time check_kernel_sections_mem() will be altered/fixed, nobody
will understand why Octeon still has this workaround.

-- 
Best regards,
Alexander Sverdlin.