[PATCH] powerpc: Fix fatal SLB miss when restoring PPR
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: 2013-11-05 05:33:27
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
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> ---
diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
index 8deaaad..3c1acc3 100644
--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h@@ -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 /*
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 12679cd..bbfb029 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S@@ -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