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Subject[PATCH 4.19 077/321] arm64: preempt: Fix big-endian when checking preempt count in assembly
Date
From: Will Deacon <will.deacon@arm.com>

[ Upstream commit 7faa313f05cad184e8b17750f0cbe5216ac6debb ]

Commit 396244692232 ("arm64: preempt: Provide our own implementation of
asm/preempt.h") extended the preempt count field in struct thread_info
to 64 bits, so that it consists of a 32-bit count plus a 32-bit flag
indicating whether or not the current task needs rescheduling.

Whilst the asm-offsets definition of TSK_TI_PREEMPT was updated to point
to this new field, the assembly usage was left untouched meaning that a
32-bit load from TSK_TI_PREEMPT on a big-endian machine actually returns
the reschedule flag instead of the count.

Whilst we could fix this by pointing TSK_TI_PREEMPT at the count field,
we're actually better off reworking the two assembly users so that they
operate on the whole 64-bit value in favour of inspecting the thread
flags separately in order to determine whether a reschedule is needed.

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/include/asm/assembler.h | 8 +++-----
arch/arm64/kernel/entry.S | 6 ++----
2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 5a97ac8531682..0c100506a29aa 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -683,11 +683,9 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
.macro if_will_cond_yield_neon
#ifdef CONFIG_PREEMPT
get_thread_info x0
- ldr w1, [x0, #TSK_TI_PREEMPT]
- ldr x0, [x0, #TSK_TI_FLAGS]
- cmp w1, #PREEMPT_DISABLE_OFFSET
- csel x0, x0, xzr, eq
- tbnz x0, #TIF_NEED_RESCHED, .Lyield_\@ // needs rescheduling?
+ ldr x0, [x0, #TSK_TI_PREEMPT]
+ sub x0, x0, #PREEMPT_DISABLE_OFFSET
+ cbz x0, .Lyield_\@
/* fall through to endif_yield_neon */
.subsection 1
.Lyield_\@ :
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 5f800384cb9a8..bb68323530458 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -622,10 +622,8 @@ el1_irq:
irq_handler

#ifdef CONFIG_PREEMPT
- ldr w24, [tsk, #TSK_TI_PREEMPT] // get preempt count
- cbnz w24, 1f // preempt count != 0
- ldr x0, [tsk, #TSK_TI_FLAGS] // get flags
- tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?
+ ldr x24, [tsk, #TSK_TI_PREEMPT] // get preempt count
+ cbnz x24, 1f // preempt count != 0
bl el1_preempt
1:
#endif
--
2.20.1


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