powerpc/32s: Use SPRN_SPRG_SCRATCH2 in DSI prolog

Use SPRN_SPRG_SCRATCH2 as an alternative scratch register in
the early part of DSI prolog in order to avoid clobbering
SPRN_SPRG_SCRATCH0/1 used by other prologs.

The 603 doesn't like a jump from DataLoadTLBMiss to the 10 nops
that are now in the beginning of DSI exception as a result of
the feature section. To workaround this, add a jump as alternative.
It also avoids fetching 10 nops for nothing.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f9f8df2a2be93568768ef1ac793639f7914cf103.1606285014.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 0978a9a..ee645e7 100644 (file)
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1204,6 +1204,7 @@
 #ifdef CONFIG_PPC_BOOK3S_32
 #define SPRN_SPRG_SCRATCH0     SPRN_SPRG0
 #define SPRN_SPRG_SCRATCH1     SPRN_SPRG1
+#define SPRN_SPRG_SCRATCH2     SPRN_SPRG2
 #define SPRN_SPRG_603_LRU      SPRN_SPRG4
 #endif
 

diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 8cc83ce..a93c75c 100644 (file)
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S
@@ -288,9 +288,9 @@ MachineCheck:
        DO_KVM  0x300
 DataAccess:
 #ifdef CONFIG_VMAP_STACK
-       mtspr   SPRN_SPRG_SCRATCH0,r10
-       mfspr   r10, SPRN_SPRG_THREAD
 BEGIN_MMU_FTR_SECTION
+       mtspr   SPRN_SPRG_SCRATCH2,r10
+       mfspr   r10, SPRN_SPRG_THREAD
        stw     r11, THR11(r10)
        mfspr   r10, SPRN_DSISR
        mfcr    r11
@@ -304,19 +304,11 @@ BEGIN_MMU_FTR_SECTION
 .Lhash_page_dsi_cont:
        mtcr    r11
        lwz     r11, THR11(r10)
-END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
-       mtspr   SPRN_SPRG_SCRATCH1,r11
-       mfspr   r11, SPRN_DAR
-       stw     r11, DAR(r10)
-       mfspr   r11, SPRN_DSISR
-       stw     r11, DSISR(r10)
-       mfspr   r11, SPRN_SRR0
-       stw     r11, SRR0(r10)
-       mfspr   r11, SPRN_SRR1          /* check whether user or kernel */
-       stw     r11, SRR1(r10)
-       mfcr    r10
-       andi.   r11, r11, MSR_PR
-
+       mfspr   r10, SPRN_SPRG_SCRATCH2
+MMU_FTR_SECTION_ELSE
+       b       1f
+ALT_MMU_FTR_SECTION_END_IFSET(MMU_FTR_HPTE_TABLE)
+1:     EXCEPTION_PROLOG_0 handle_dar_dsisr=1
        EXCEPTION_PROLOG_1
        b       handle_page_fault_tramp_1
 #else  /* CONFIG_VMAP_STACK */
@@ -764,7 +756,7 @@ fast_hash_page_return:
        /* DSI */
        mtcr    r11
        lwz     r11, THR11(r10)
-       mfspr   r10, SPRN_SPRG_SCRATCH0
+       mfspr   r10, SPRN_SPRG_SCRATCH2
        rfi
 
 1:     /* ISI */