path: root/arch/arc
diff options
authorVineet Gupta <vgupta@synopsys.com>2019-04-09 19:16:37 -0700
committerVineet Gupta <vgupta@synopsys.com>2019-07-01 11:02:22 -0700
commit23c0cbd0c75c3b564850294427fd2be2bc2a015b (patch)
tree1d21578cc359eddd8f3ab6f58bb4a0a77de4ddb0 /arch/arc
parent45869eb0c0afd72bd5ab2437d4b00915697c044a (diff)
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')
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
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 -----------
+ ; 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
; Restore the 4-scratch regs saved by fast path miss handler