• Matt Bennett's avatar
    MIPS: Octeon: Fix kernel panic on startup from memory corruption · 66803dd9
    Matt Bennett authored
    
    
    During development it was found that a number of builds would panic
    during the kernel init process, more specifically in 'delayed_fput()'.
    The panic showed the kernel trying to access a memory address of
    '0xb7fdc00' while traversing the 'delayed_fput_list' structure.
    Comparing this memory address to the value of the pointer used on
    builds that did not panic confirmed that the pointer on crashing
    builds must have been corrupted at some stage earlier in the init
    process.
    
    By traversing the list earlier and earlier in the code it was found
    that 'plat_mem_setup()' was responsible for corrupting the list.
    Specifically the line:
    
        memory = cvmx_bootmem_phy_alloc(mem_alloc_size,
    			__pa_symbol(&__init_end), -1,
    			0x100000,
    			CVMX_BOOTMEM_FLAG_NO_LOCKING);
    
    Which would eventually call:
    
        cvmx_bootmem_phy_set_size(new_ent_addr,
    		cvmx_bootmem_phy_get_size
    		(ent_addr) -
    		(desired_min_addr -
    			ent_addr));
    
    Where 'new_ent_addr'=0x4800000 (the address of 'delayed_fput_list')
    and the second argument (size)=0xb7fdc00 (the address causing the
    kernel panic). The job of this part of 'plat_mem_setup()' is to
    allocate chunks of memory for the kernel to use. At the start of
    each chunk of memory the size of the chunk is written, hence the
    value 0xb7fdc00 is written onto memory at 0x4800000, therefore the
    kernel panics when it goes back to access 'delayed_fput_list' later
    on in the initialisation process.
    
    On builds that were not crashing it was found that the compiler had
    placed 'delayed_fput_list' at 0x4800008, meaning it wasn't corrupted
    (but something else in memory was overwritten).
    
    As can be seen in the first function call above the code begins to
    allocate chunks of memory beginning from the symbol '__init_end'.
    The MIPS linker script (vmlinux.lds.S) however defines the .bss
    section to begin after '__init_end'. Therefore memory within the
    .bss section is allocated to the kernel to use (System.map shows
    'delayed_fput_list' and other kernel structures to be in .bss).
    
    To stop the kernel panic (and the .bss section being corrupted)
    memory should begin being allocated from the symbol '_end'.
    Signed-off-by: default avatarMatt Bennett <matt.bennett@alliedtelesis.co.nz>
    Acked-by: default avatarDavid Daney <david.daney@cavium.com>
    Cc: linux-mips@linux-mips.org
    Cc: aleksey.makarov@auriga.com
    Patchwork: https://patchwork.linux-mips.org/patch/11251/
    
    Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    66803dd9
setup.c 31.2 KB