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powerpc: Fix fatal SLB miss when restoring PPR

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When restoring the PPR value, we incorrectly access the thread structure
at a time where MSR:RI is clear, which means we cannot recover from nested
faults. However the thread structure isn't covered by the "bolted" SLB
entries and thus accessing can fault.

This fixes it by splitting the code so that the PPR value is loaded into
a GPR before MSR:RI is cleared.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Benjamin Herrenschmidt 2013-11-05 16:33:22 +11:00
parent 36954dc78d
commit 0c4888ef1d
2 changed files with 9 additions and 8 deletions
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7
arch/powerpc/include/asm/ppc_asm.h
View file

@ -406,13 +406,6 @@ BEGIN_FTR_SECTION_NESTED(945) \
std ra,TASKTHREADPPR(rb); \
END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,945)
#define RESTORE_PPR(ra, rb) \
BEGIN_FTR_SECTION_NESTED(946) \
ld ra,PACACURRENT(r13); \
ld rb,TASKTHREADPPR(ra); \
mtspr SPRN_PPR,rb; /* Restore PPR */ \
END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,946)
#endif
/*

10
arch/powerpc/kernel/entry_64.S
View file

@ -818,6 +818,12 @@ fast_exception_return:
andi. r0,r3,MSR_RI
beq- unrecov_restore
/* Load PPR from thread struct before we clear MSR:RI */
BEGIN_FTR_SECTION
ld r2,PACACURRENT(r13)
ld r2,TASKTHREADPPR(r2)
END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
/*
* Clear RI before restoring r13. If we are returning to
* userspace and we take an exception after restoring r13,
@ -838,8 +844,10 @@ fast_exception_return:
*/
andi. r0,r3,MSR_PR
beq 1f
BEGIN_FTR_SECTION
mtspr SPRN_PPR,r2 /* Restore PPR */
END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
ACCOUNT_CPU_USER_EXIT(r2, r4)
RESTORE_PPR(r2, r4)
REST_GPR(13, r1)
1:
mtspr SPRN_SRR1,r3