linux

iv/linux

History

Vineet Gupta 648d4e3957 ARCv2: entry: push out the Z flag unclobber from common EXCEPTION_PROLOGUE

[ Upstream commit 23c0cbd0c75c3b564850294427fd2be2bc2a015b ]

Upon a taken interrupt/exception from User mode, HS hardware auto sets Z flag.
This helps shave a few instructions from EXCEPTION_PROLOGUE by eliding
re-reading ERSTATUS and some bit fiddling.

However TLB Miss Exception handler can clobber the CPU flags and still end
up in EXCEPTION_PROLOGUE in the slow path handling TLB handling case:

   EV_TLBMissD
     do_slow_path_pf
       EV_TLBProtV (aliased to call_do_page_fault)
          EXCEPTION_PROLOGUE

As a result, EXCEPTION_PROLOGUE need to "unclobber" the Z flag which this
patch changes. It is now pushed out to TLB Miss Exception handler.
The reasons beings:

 - The flag restoration is only needed for slowpath TLB Miss Exception
   handling, but currently being in EXCEPTION_PROLOGUE penalizes all
   exceptions such as ProtV and syscall Trap, where Z flag is already
   as expected.

 - Pushing unclobber out to where it was clobbered is much cleaner and
   also serves to document the fact.

 - Makes EXCEPTION_PROLGUE similar to INTERRUPT_PROLOGUE so easier to
   refactor the common parts which is what this series aims to do

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Stable-dep-of: 92e2921eeafd ("ARC: define ASM_NL and __ALIGN(_STR) outside #ifdef __ASSEMBLY__ guard")
Signed-off-by: Sasha Levin <sashal@kernel.org>

2023-08-11 11:45:10 +02:00

cache.c

ARC: export clear_user_page() for modules

2021-09-22 11:48:13 +02:00

dma.c

ARC: don't check for HIGHMEM pages in arch_dma_alloc

2018-09-04 13:21:38 -07:00

extable.c

ARC: uaccess: enable INLINE_COPY_{TO,FROM}_USER ...

2017-03-30 00:07:48 -04:00

fault.c

ARC: mm: SIGSEGV userspace trying to access kernel virtual memory