Re: [PATCH] MIPS: Alchemy: Save the Ethernet address before reusing PROM memory

[Florian Fainelli <f.fainelli@gmail.com>]

On 10/16/26 12:45, Matthew Wilcox wrote:
> On Fri, Oct 16, 2026 at 10:31:55AM -0700, Florian Fainelli wrote:
>> Alchemy keeps pointers into the firmware environment and looks up ethaddr
>> when initializing the Ethernet devices. By that point, memory allocation
>> can have overwritten the environment, causing prom_getenv() to pass an
>> invalid pointer to strchr() and panic during boot.
>>
>> On the MTX-1, the struct page layout change in 9ddb3c14afba reduces struct
>> page from 40 to 32 bytes and exposes this unreserved firmware memory.
>> Bisection and boot tests confirmed that the parent boots while the change
>> reproduces the panic.
>>
>> Parse the Ethernet address during prom_init(), before registering RAM
>> with memblock, and keep the six bytes in kernel-owned init data. Return
>> the saved address during device initialization, preserving the existing
>> YAMON formats and command-line fallback without reserving a fixed
>> low-memory region.
>>
>> Fixes: 9ddb3c14afba ("mm: fix struct page layout on 32-bit systems")
> 
> This is an inappropriate Fixes line.  That may have exposed the problem
> (... 5 years ago; how often is this being tested?) but it's merely
> restoring the layout to that which existed two years before that.
> The correct Fixes line wuld be something related to this driver.

Fair enough, because this landed as a the first bad commit, I used it as 
is, but you have a good point about this being a pre-existing issue that 
just became apparent with 9ddb3c14afba.

As for how often the platform was tested, not very often clearly, but 
that's about to change since I have it restored in my test rack.

Thanks
-- 
Florian