[PATCH 3.13 069/103] ARM: 8128/1: abort: don't clear the exclusive monitors

From: Kamal Mostafa
Date: Tue Sep 30 2014 - 18:02:52 EST -stable review patch. If anyone has any objections, please let me know.


From: Mark Rutland <mark.rutland@xxxxxxx>

commit 85868313177700d20644263a782351262d2aff84 upstream.

The ARMv6 and ARMv7 early abort handlers clear the exclusive monitors
upon entry to the kernel, but this is redundant:

- We clear the monitors on every exception return since commit
200b812d0084 ("Clear the exclusive monitor when returning from an
exception"), so this is not necessary to ensure the monitors are
cleared before returning from a fault handler.

- Any dummy STREX will target a temporary scratch area in memory, and
may succeed or fail without corrupting useful data. Its status value
will not be used.

- Any other STREX in the kernel must be preceded by an LDREX, which
will initialise the monitors consistently and will not depend on the
earlier state of the monitors.

Therefore we have no reason to care about the initial state of the
exclusive monitors when a data abort is taken, and clearing the monitors
prior to exception return (as we already do) is sufficient.

This patch removes the redundant clearing of the exclusive monitors from
the early abort handlers.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
arch/arm/mm/abort-ev6.S | 6 ------
arch/arm/mm/abort-ev7.S | 6 ------
2 files changed, 12 deletions(-)

diff --git a/arch/arm/mm/abort-ev6.S b/arch/arm/mm/abort-ev6.S
index 3815a82..8c48c5c 100644
--- a/arch/arm/mm/abort-ev6.S
+++ b/arch/arm/mm/abort-ev6.S
@@ -17,12 +17,6 @@
.align 5
-#ifdef CONFIG_CPU_V6
- sub r1, sp, #4 @ Get unused stack location
- strex r0, r1, [r1] @ Clear the exclusive monitor
-#elif defined(CONFIG_CPU_32v6K)
- clrex
mrc p15, 0, r1, c5, c0, 0 @ get FSR
mrc p15, 0, r0, c6, c0, 0 @ get FAR
diff --git a/arch/arm/mm/abort-ev7.S b/arch/arm/mm/abort-ev7.S
index 7033752..4812ad0 100644
--- a/arch/arm/mm/abort-ev7.S
+++ b/arch/arm/mm/abort-ev7.S
@@ -13,12 +13,6 @@
.align 5
- /*
- * The effect of data aborts on on the exclusive access monitor are
- * UNPREDICTABLE. Do a CLREX to clear the state
- */
- clrex
mrc p15, 0, r1, c5, c0, 0 @ get FSR
mrc p15, 0, r0, c6, c0, 0 @ get FAR


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