powerpc/mm: Pre-filter SRR1 bits before do_page_fault()

By filtering the relevant SRR1 bits in the assembly rather than
in do_page_fault() itself, we avoid a conditional branch (since we
already come from different path for data and instruction faults).

This will allow more simplifications later

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/head_32.S

@@ -409,7 +409,7 @@ InstructionAccess:
 	mr	r4,r12			/* SRR0 is fault address */
 	bl	hash_page
 1:	mr	r4,r12
-	mr	r5,r9
+	andis.	r5,r9,0x4820		/* Filter relevant SRR1 bits */
 	EXC_XFER_LITE(0x400, handle_page_fault)
 
 /* External interrupt */

arch/powerpc/kernel/head_8xx.S

@@ -569,8 +569,8 @@ _ENTRY(DTLBMiss_jmp)
 InstructionTLBError:
 	EXCEPTION_PROLOG
 	mr	r4,r12
-	mr	r5,r9
-	andis.	r10,r5,0x4000
+	andis.	r5,r9,0x4820		/* Filter relevant SRR1 bits */
+	andis.	r10,r9,0x4000
 	beq+	1f
 	tlbie	r4
 itlbie:

arch/powerpc/mm/fault.c

@@ -203,23 +203,13 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 	int code = SEGV_MAPERR;
 	int is_write = 0;
-	int trap = TRAP(regs);
- 	int is_exec = trap == 0x400;
+ 	int is_exec = TRAP(regs) == 0x400;
 	int is_user = user_mode(regs);
 	int fault;
 	int rc = 0, store_update_sp = 0;
 
 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
-	/*
-	 * Fortunately the bit assignments in SRR1 for an instruction
-	 * fault and DSISR for a data fault are mostly the same for the
-	 * bits we are interested in.  But there are some bits which
-	 * indicate errors in DSISR but can validly be set in SRR1.
-	 */
-	if (is_exec)
-		error_code &= 0x48200000;
-	else
-		is_write = error_code & DSISR_ISSTORE;
+	is_write = error_code & DSISR_ISSTORE;
 #else
 	is_write = error_code & ESR_DST;
 #endif /* CONFIG_4xx || CONFIG_BOOKE */