Re: [PATCH 5.10 103/157] MIPS: kernel: Reserve exception base early to prevent corruption

[Naresh Kamboju]

On Mon, 22 Mar 2021 at 18:14, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
>
> [ Upstream commit bd67b711bfaa02cf19e88aa2d9edae5c1c1d2739 ]
>
> 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>
> Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Tested-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Reviewed-by: Serge Semin <fancer.lancer@xxxxxxxxx>
> Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  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 +++++-----

mipc tinyconfig and allnoconfig builds failed on stable-rc 5.10 branch

make --silent --keep-going --jobs=8
O=/home/tuxbuild/.cache/tuxmake/builds/1/tmp ARCH=mips
CROSS_COMPILE=mips-linux-gnu- 'CC=sccache mips-linux-gnu-gcc'
'HOSTCC=sccache gcc'
WARNING: modpost: vmlinux.o(.text+0x6a88): Section mismatch in
reference from the function reserve_exception_space() to the function
.meminit.text:memblock_reserve()
The function reserve_exception_space() references
the function __meminit memblock_reserve().
This is often because reserve_exception_space lacks a __meminit
annotation or the annotation of memblock_reserve is wrong.

FATAL: modpost: Section mismatches detected.
Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
make[2]: *** [/builds/linux/scripts/Makefile.modpost:59:
vmlinux.symvers] Error 1

Here is the list of build failed,
 - gcc-8-allnoconfig
 - gcc-8-tinyconfig
 - gcc-9-allnoconfig
 - gcc-9-tinyconfig
 - gcc-10-allnoconfig
 - gcc-10-tinyconfig
 - clang-10-tinyconfig
 - clang-10-allnoconfig
 - clang-11-allnoconfig
 - clang-11-tinyconfig
 - clang-12-tinyconfig
 - clang-12-allnoconfig

Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>

link:
https://gitlab.com/Linaro/lkft/mirrors/stable/linux-stable-rc/-/jobs/1117167411#L142

steps to reproduce:
---------------------------
# TuxMake is a command line tool and Python library that provides
# portable and repeatable Linux kernel builds across a variety of
# architectures, toolchains, kernel configurations, and make targets.
#
# TuxMake supports the concept of runtimes.
# See https://docs.tuxmake.org/runtimes/, for that to work it requires
# that you install podman or docker on your system.
#
# To install tuxmake on your system globally:
# sudo pip3 install -U tuxmake
#
# See https://docs.tuxmake.org/ for complete documentation.


tuxmake --runtime podman --target-arch mips --toolchain gcc-10
--kconfig tinyconfig


--
Linaro LKFT
https://lkft.linaro.org