powerpc/64: Interrupts save PPR on stack rather than thread_struct

PPR is the odd register out when it comes to interrupt handling, it is
saved in current->thread.ppr while all others are saved on the stack.

The difficulty with this is that accessing thread.ppr can cause a SLB
fault, but the SLB fault handler implementation in C change had
assumed the normal exception entry handlers would not cause an SLB
fault.

Fix this by allocating room in the interrupt stack to save PPR.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/exception-64s.h

@@ -236,11 +236,10 @@
  * PPR save/restore macros used in exceptions_64s.S  
  * Used for P7 or later processors
  */
-#define SAVE_PPR(area, ra, rb)						\
+#define SAVE_PPR(area, ra)						\
 BEGIN_FTR_SECTION_NESTED(940)						\
-	ld	ra,PACACURRENT(r13);					\
-	ld	rb,area+EX_PPR(r13);	/* Read PPR from paca */	\
-	std	rb,TASKTHREADPPR(ra);					\
+	ld	ra,area+EX_PPR(r13);	/* Read PPR from paca */	\
+	std	ra,_PPR(r1);						\
 END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,940)
 
 #define RESTORE_PPR_PACA(area, ra)					\
@@ -508,7 +507,7 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 3:	EXCEPTION_PROLOG_COMMON_1();					   \
 	beq	4f;			/* if from kernel mode		*/ \
 	ACCOUNT_CPU_USER_ENTRY(r13, r9, r10);				   \
-	SAVE_PPR(area, r9, r10);					   \
+	SAVE_PPR(area, r9);						   \
 4:	EXCEPTION_PROLOG_COMMON_2(area)					   \
 	EXCEPTION_PROLOG_COMMON_3(n)					   \
 	ACCOUNT_STOLEN_TIME

arch/powerpc/include/asm/processor.h

@@ -32,9 +32,9 @@
 /* Default SMT priority is set to 3. Use 11- 13bits to save priority. */
 #define PPR_PRIORITY 3
 #ifdef __ASSEMBLY__
-#define INIT_PPR (PPR_PRIORITY << 50)
+#define DEFAULT_PPR (PPR_PRIORITY << 50)
 #else
-#define INIT_PPR ((u64)PPR_PRIORITY << 50)
+#define DEFAULT_PPR ((u64)PPR_PRIORITY << 50)
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_PPC64 */
 
@@ -341,7 +341,6 @@ struct thread_struct {
 	 * onwards.
 	 */
 	int		dscr_inherit;
-	unsigned long	ppr;	/* used to save/restore SMT priority */
 	unsigned long	tidr;
 #endif
 #ifdef CONFIG_PPC_BOOK3S_64
@@ -389,7 +388,6 @@ struct thread_struct {
 	.regs = (struct pt_regs *)INIT_SP - 1, /* XXX bogus, I think */ \
 	.addr_limit = KERNEL_DS, \
 	.fpexc_mode = 0, \
-	.ppr = INIT_PPR, \
 	.fscr = FSCR_TAR | FSCR_EBB \
 }
 #endif

arch/powerpc/include/asm/ptrace.h

@@ -51,6 +51,10 @@ struct pt_regs
 			unsigned long result;
 		};
 	};
+
+#ifdef CONFIG_PPC64
+	unsigned long ppr;
+#endif
 };
 #endif