This is a note to let you know that I've just added the patch titled
ARCv2: entry: push out the Z flag unclobber from common EXCEPTION_PROLOGUE
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arcv2-entry-push-out-the-z-flag-unclobber-from-commo.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit e4c727839b77a24016fb973f42e27538b4d5f0b9
Author: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Date: Tue Apr 9 19:16:37 2019 -0700
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@xxxxxxxxxxxx>
Stable-dep-of: 92e2921eeafd ("ARC: define ASM_NL and __ALIGN(_STR) outside #ifdef __ASSEMBLY__ guard")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
index 1c3520d1fa420..3209a67629606 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 0e1e47a67c736..e50cac799a518 100644
--- a/arch/arc/mm/tlbex.S
+++ b/arch/arc/mm/tlbex.S
@@ -396,6 +396,17 @@ 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
