2
0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-25 21:54:06 +08:00
linux-next/arch/arc
Vineet Gupta 3a715e8040 ARC: fp: set FPU_STATUS.FWE to enable FPU_STATUS update on context switch
FPU_STATUS register contains FP exception flags bits which are updated
by core as side-effect of FP instructions but can also be manually
wiggled such as by glibc C99 functions fe{raise,clear,test}except() etc.
To effect the update, the programming model requires OR'ing FWE
bit (31). This bit is write-only and RAZ, meaning it is effectively
auto-cleared after write and thus needs to be set everytime: which
is how glibc implements this.

However there's another usecase of FPU_STATUS update, at the time of
Linux task switch when incoming task value needs to be programmed into
the register. This was added as part of f45ba2bd6d ("ARCv2:
fpu: preserve userspace fpu state") which missed OR'ing FWE bit,
meaning the new value is effectively not being written at all.
This patch remedies that.

Interestingly, this snafu was not caught in interm glibc testing as the
race window which relies on a specific exception bit to be set/clear is
really small specially when it nvolves context switch.
Fortunately this was caught by glibc's math/test-fenv-tls test which
repeatedly set/clear exception flags in a big loop, concurrently in main
program and also in a thread.

Fixes: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/54
Fixes: f45ba2bd6d ("ARCv2: fpu: preserve userspace fpu state")
Cc: stable@vger.kernel.org	#5.6+
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
2021-08-03 18:58:33 -07:00
..
boot ARC: haps: bump memory to 1 GB 2021-03-12 07:22:23 -08:00
configs ARC: [plat-eznps]: Drop support for EZChip NPS platform 2020-10-05 21:02:29 -07:00
include arc: Prefer unsigned int to bare use of unsigned 2021-08-03 18:58:33 -07:00
kernel ARC: fp: set FPU_STATUS.FWE to enable FPU_STATUS update on context switch 2021-08-03 18:58:33 -07:00
lib treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
mm arc: convert to setup_initial_init_mm() 2021-07-08 11:48:21 -07:00
plat-axs10x treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
plat-hsdk ARC: [hsdk]: Enable FPU_SAVE_RESTORE 2021-01-08 13:46:58 -08:00
plat-sim ARC: merge HAPS-HS with nSIM-HS configs 2019-10-28 12:12:31 -07:00
plat-tb10x treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 333 2019-06-05 17:37:06 +02:00
Kbuild treewide: Add SPDX license identifier - Kbuild 2019-05-30 11:32:33 -07:00
Kconfig arc: Fix spelling mistake and grammar in Kconfig 2021-08-03 18:58:33 -07:00
Kconfig.debug Kconfig: consolidate the "Kernel hacking" menu 2018-08-02 08:06:48 +09:00
Makefile kbuild: require all architectures to have arch/$(SRCARCH)/Kbuild 2021-05-26 23:10:37 +09:00