powerpc: Don't use thread struct for saving SRR0/1 on syscall.

CR0 can be saved later, and CTR can also be used for saving.

Keep SRR1 in r9 and stash SRR0 in CTR, this avoids using thread_struct
in memory for that.

Saves 3 cycles (ie 1%) in null_syscall selftest on 8xx.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b94c3bc03bac9431fec2dadb686384c481889422.1580470483.git.christophe.leroy@c-s.fr

diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 0e7bf28..4a1faed 100644 (file)
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -114,28 +114,23 @@
        mfspr   r9, SPRN_SRR1
 #ifdef CONFIG_VMAP_STACK
        mfspr   r11, SPRN_SRR0
-       stw     r11, SRR0(r12)
-       stw     r9, SRR1(r12)
+       mtctr   r11
 #endif
-       mfcr    r10
        andi.   r11, r9, MSR_PR
        lwz     r11,TASK_STACK-THREAD(r12)
        beq-    99f
-       rlwinm  r10,r10,0,4,2   /* Clear SO bit in CR */
        addi    r11, r11, THREAD_SIZE - INT_FRAME_SIZE
 #ifdef CONFIG_VMAP_STACK
-       li      r9, MSR_KERNEL & ~(MSR_IR | MSR_RI) /* can take DTLB miss */
-       mtmsr   r9
+       li      r10, MSR_KERNEL & ~(MSR_IR | MSR_RI) /* can take DTLB miss */
+       mtmsr   r10
        isync
 #endif
        tovirt_vmstack r12, r12
        tophys_novmstack r11, r11
-       stw     r10,_CCR(r11)           /* save registers */
        mflr    r10
        stw     r10, _LINK(r11)
 #ifdef CONFIG_VMAP_STACK
-       lwz     r10, SRR0(r12)
-       lwz     r9, SRR1(r12)
+       mfctr   r10
 #else
        mfspr   r10,SPRN_SRR0
 #endif
@@ -143,6 +138,9 @@
        stw     r1,0(r11)
        tovirt_novmstack r1, r11        /* set new kernel sp */
        stw     r10,_NIP(r11)
+       mfcr    r10
+       rlwinm  r10,r10,0,4,2   /* Clear SO bit in CR */
+       stw     r10,_CCR(r11)           /* save registers */
 #ifdef CONFIG_40x
        rlwinm  r9,r9,0,14,12           /* clear MSR_WE (necessary?) */
 #else