[POWERPC] Avoid unpaired stwcx. on some processors
The context switch code in the kernel issues a dummy stwcx. to clear the
reservation, as recommended by the architecture. However, some processors
can have issues if this stwcx to address A occurs while the reservation
is already held to a different address B. To avoid this problem, the dummy
stwcx. needs to be paired with a dummy lwarx to the same address.
This adds the dummy lwarx, and creates a cpu feature bit to indicate
which cpus are affected. Tested on mpc8641_hpcn_defconfig in
arch/powerpc; build tested in arch/ppc.
Signed-off-by: Becky Bruce <becky.bruce@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index a7572cf..69a91bd 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -251,6 +251,9 @@
bne- 2f
1:
#endif /* CONFIG_44x */
+BEGIN_FTR_SECTION
+ lwarx r7,0,r1
+END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
stwcx. r0,0,r1 /* to clear the reservation */
lwz r4,_LINK(r1)
lwz r5,_CCR(r1)
@@ -717,6 +720,9 @@
mtctr r11
PPC405_ERR77(0,r1)
+BEGIN_FTR_SECTION
+ lwarx r11,0,r1
+END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
stwcx. r0,0,r1 /* to clear the reservation */
#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))