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Subject[PATCH v5 16/17] powerpc/32s: avoid crossing page boundary while changing SRR0/1.
Date
Trying VMAP_STACK with KVM, vmlinux was not starting.
This was due to SRR0 and SRR1 clobbered by an ISI due to
the rfi being in a different page than the mtsrr0/1:

c0003fe0 <mmu_off>:
c0003fe0: 38 83 00 54 addi r4,r3,84
c0003fe4: 7c 60 00 a6 mfmsr r3
c0003fe8: 70 60 00 30 andi. r0,r3,48
c0003fec: 4d 82 00 20 beqlr
c0003ff0: 7c 63 00 78 andc r3,r3,r0
c0003ff4: 7c 9a 03 a6 mtsrr0 r4
c0003ff8: 7c 7b 03 a6 mtsrr1 r3
c0003ffc: 7c 00 04 ac hwsync
c0004000: 4c 00 00 64 rfi

Align the 4 instruction block used to deactivate MMU to order 4,
so that the block never crosses a page boundary.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/kernel/head_32.S | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 7ec780858299..90ef355e958b 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -917,6 +917,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
ori r4,r4,2f@l
tophys(r4,r4)
li r3,MSR_KERNEL & ~(MSR_IR|MSR_DR)
+
+ .align 4
mtspr SPRN_SRR0,r4
mtspr SPRN_SRR1,r3
SYNC
@@ -1058,6 +1060,8 @@ _ENTRY(update_bats)
rlwinm r0, r6, 0, ~MSR_RI
rlwinm r0, r0, 0, ~MSR_EE
mtmsr r0
+
+ .align 4
mtspr SPRN_SRR0, r4
mtspr SPRN_SRR1, r3
SYNC
@@ -1097,6 +1101,8 @@ mmu_off:
andi. r0,r3,MSR_DR|MSR_IR /* MMU enabled? */
beqlr
andc r3,r3,r0
+
+ .align 4
mtspr SPRN_SRR0,r4
mtspr SPRN_SRR1,r3
sync
--
2.13.3
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