[PATCH] ARM: cache-v7: Disable preemption when reading CCSIDR

From: Stephen Boyd
Date: Thu Feb 02 2012 - 14:24:50 EST

armv7's flush_cache_all() flushes caches via set/way. To
determine the cache attributes (line size, number of sets,
etc.) the assembly first writes the CSSELR register to select a
cache level and then reads the CCSIDR register. The CSSELR register
is banked per-cpu and is used to determine which cache level CCSIDR
reads. If the task is migrated between when the CSSELR is written and
the CCSIDR is read the CCSIDR value may be for an unexpected cache
level (for example L1 instead of L2) and incorrect cache flushing
could occur.

Disable preemption across the write and read so that the correct
cache attributes are read and used for the cache flushing
routine. This fixes a problem we see in scm_call() when
flush_cache_all() is called from preemptible context and
sometimes the L2 cache is not properly flushed out.

Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>

Should we move get_thread_info into assembler.h? It seems odd
to include entry-header.S but I saw that vfp was doing the same.

arch/arm/mm/cache-v7.S | 11 +++++++++++
1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mm/cache-v7.S b/arch/arm/mm/cache-v7.S
index 07c4bc8..a033858 100644
--- a/arch/arm/mm/cache-v7.S
+++ b/arch/arm/mm/cache-v7.S
@@ -16,6 +16,7 @@
#include <asm/unwind.h>

#include "proc-macros.S"
+#include "../kernel/entry-header.S"

* v7_flush_icache_all()
@@ -54,9 +55,19 @@ loop1:
and r1, r1, #7 @ mask of the bits for current cache only
cmp r1, #2 @ see what cache we have at this level
blt skip @ skip if no cache, or just i-cache
+ get_thread_info r9
+ ldr r11, [r9, #TI_PREEMPT] @ get preempt count
+ add r11, r11, #1 @ increment it
+ str r11, [r9, #TI_PREEMPT]
mcr p15, 2, r10, c0, c0, 0 @ select current cache level in cssr
isb @ isb to sych the new cssr&csidr
mrc p15, 1, r1, c0, c0, 0 @ read the new csidr
+ sub r11, r11, #1 @ decrement preempt count
+ str r11, [r9, #TI_PREEMPT]
and r2, r1, #7 @ extract the length of the cache lines
add r2, r2, #4 @ add 4 (line length offset)
ldr r4, =0x3ff
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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