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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/mm
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/mm')
-rw-r--r--arch/arc/mm/tlbex.S11
1 files changed, 11 insertions, 0 deletions
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