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| author | Vineet Gupta | 2019-04-10 04:16:37 +0200 |
|---|---|---|
| committer | Vineet Gupta | 2019-07-01 20:02:22 +0200 |
| commit | 23c0cbd0c75c3b564850294427fd2be2bc2a015b (patch) | |
| tree | 1d21578cc359eddd8f3ab6f58bb4a0a77de4ddb0 /arch/arc | |
| parent | ARCv2: entry: comments about hardware auto-save on taken interrupts (diff) | |
| download | kernel-qcow2-linux-23c0cbd0c75c3b564850294427fd2be2bc2a015b.tar.gz kernel-qcow2-linux-23c0cbd0c75c3b564850294427fd2be2bc2a015b.tar.xz kernel-qcow2-linux-23c0cbd0c75c3b564850294427fd2be2bc2a015b.zip | |
ARCv2: entry: push out the Z flag unclobber from common EXCEPTION_PROLOGUE
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>
Diffstat (limited to 'arch/arc')
| -rw-r--r-- | arch/arc/include/asm/entry-arcv2.h | 8 | ||||
| -rw-r--r-- | arch/arc/mm/tlbex.S | 11 |
2 files changed, 11 insertions, 8 deletions
diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h index 1c3520d1fa42..3209a6762960 100644 --- a/arch/arc/include/asm/entry-arcv2.h +++ b/arch/arc/include/asm/entry-arcv2.h @@ -225,14 +225,6 @@ ; -- for interrupts, regs above are auto-saved by h/w in that order -- ; Now do what ISR prologue does (manually save r12, sp, fp, gp, r25) - ; - ; Set Z flag if this was from U mode (expected by INTERRUPT_PROLOGUE) - ; Although H/w exception micro-ops do set Z flag for U mode (just like - ; for interrupts), it could get clobbered in case we soft land here from - ; a TLB Miss exception handler (tlbex.S) - - and r10, r10, STATUS_U_MASK - xor.f 0, r10, STATUS_U_MASK INTERRUPT_PROLOGUE exception diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S index 471a97bf492d..c55d95dd2f39 100644 --- a/arch/arc/mm/tlbex.S +++ b/arch/arc/mm/tlbex.S @@ -393,6 +393,17 @@ EV_TLBMissD_fast_ret: ; additional label for VDK OS-kit instrumentation ;-------- Common routine to call Linux Page Fault Handler ----------- do_slow_path_pf: +#ifdef CONFIG_ISA_ARCV2 + ; Set Z flag if exception in U mode. Hardware micro-ops do this on any + ; taken interrupt/exception, and thus is already the case at the entry + ; above, but ensuing code would have already clobbered. + ; EXCEPTION_PROLOGUE called in slow path, relies on correct Z flag set + + lr r2, [erstatus] + and r2, r2, STATUS_U_MASK + bxor.f 0, r2, STATUS_U_BIT +#endif + ; Restore the 4-scratch regs saved by fast path miss handler TLBMISS_RESTORE_REGS |