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

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Message-ID: <1d6a424e-944e-7f21-1f30-989fb61018a8@nokia.com>
Date:   Mon, 9 Nov 2020 11:34:33 +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

Hello Thomas,

On 07/11/2020 10:40, Thomas Bogendoerfer 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...

-- 
Best regards,
Alexander Sverdlin.