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