On Mon, Mar 08, 2021 at 10:24:47AM +0100, Thomas Bogendoerfer wrote:
> BMIPS is one of the few platforms that do change the exception base.
> After commit 2dcb39645441 ("memblock: do not start bottom-up allocations
> with kernel_end") we started seeing BMIPS boards fail to boot with the
> built-in FDT being corrupted.
>
> Before the cited commit, early allocations would be in the [kernel_end,
> RAM_END] range, but after commit they would be within [RAM_START +
> PAGE_SIZE, RAM_END].
>
> The custom exception base handler that is installed by
> bmips_ebase_setup() done for BMIPS5000 CPUs ends-up trampling on the
> memory region allocated by unflatten_and_copy_device_tree() thus
> corrupting the FDT used by the kernel.
>
> To fix this, we need to perform an early reservation of the custom
> exception space. Additional we reserve the first 4k (1k for R3k) for
> either normal exception vector space (legacy CPUs) or special vectors
> like cache exceptions.
>
> Huge thanks to Serge for analysing and proposing a solution to this
> issue.
>
> Fixes: 2dcb39645441 ("memblock: do not start bottom-up allocations with kernel_end")
> Reported-by: Kamal Dasu <kdasu.kdev@xxxxxxxxx>
> Debugged-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> ---
> Changes in v3:
> - always reserve the first 4k for all CPUs (1k for R3k)
>
> Changes in v2:
> - do only memblock reservation in reserve_exception_space()
> - reserve 0..0x400 for all CPUs without ebase register and
> to addtional reserve_exception_space for BMIPS CPUs
>
> arch/mips/include/asm/traps.h | 3 +++
> arch/mips/kernel/cpu-probe.c | 6 ++++++
> arch/mips/kernel/cpu-r3k-probe.c | 3 +++
> arch/mips/kernel/traps.c | 10 +++++-----
> 4 files changed, 17 insertions(+), 5 deletions(-)
applied to mips-fixes.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
