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powerpc/32: Use fast instruction to set MSR RI in exception prolog on 8xx

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8xx has registers SPRN_NRI, SPRN_EID and SPRN_EIE for changing
MSR EE and RI.

Use SPRN_EID in exception prolog to set RI.

On an 8xx, it reduces the null_syscall test by 3 cycles.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/65f6bda827c2a2abce71ea7e07543e791163da33.1615552866.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2021-03-12 12:50:20 +00:00 committed by Michael Ellerman
parent 79f4bb17f1
commit e464d92b29
1 changed files with 2 additions and 0 deletions
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2
arch/powerpc/kernel/head_32.h
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@ -107,6 +107,8 @@
#endif
#ifdef CONFIG_40x
rlwinm r9,r9,0,14,12 /* clear MSR_WE (necessary?) */
#elif defined(CONFIG_PPC_8xx)
mtspr SPRN_EID, r2 /* Set MSR_RI */
#else
#ifdef CONFIG_VMAP_STACK
li r10, MSR_KERNEL & ~MSR_IR /* can take exceptions */