From 23c0cbd0c75c3b564850294427fd2be2bc2a015b Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Tue, 9 Apr 2019 19:16:37 -0700 Subject: [PATCH] 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 --- arch/arc/include/asm/entry-arcv2.h | 8 -------- 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 1c3520d..3209a67 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 471a97bf..c55d95d 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 -- 2.7.4