powerpc: rework 4xx PTE access and TLB miss

This is some preliminary work to improve TLB management on SW loaded
TLB powerpc platforms. This introduce support for non-atomic PTE
operations in pgtable-ppc32.h and removes write back to the PTE from
the TLB miss handlers. In addition, the DSI interrupt code no longer
tries to fixup write permission, this is left to generic code, and
_PAGE_HWWRITE is gone.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>

1 files changed, 96 insertions, 190 deletions

diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index 2944529..f3a1ea9 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -293,119 +293,9 @@ interrupt_base:
 	MCHECK_EXCEPTION(0x0210, MachineCheckA, machine_check_exception)
 
 	/* Data Storage Interrupt */
-	START_EXCEPTION(DataStorage)
-	mtspr	SPRN_SPRG0, r10		/* Save some working registers */
-	mtspr	SPRN_SPRG1, r11
-	mtspr	SPRN_SPRG4W, r12
-	mtspr	SPRN_SPRG5W, r13
-	mfcr	r11
-	mtspr	SPRN_SPRG7W, r11
-
-	/*
-	 * Check if it was a store fault, if not then bail
-	 * because a user tried to access a kernel or
-	 * read-protected page.  Otherwise, get the
-	 * offending address and handle it.
-	 */
-	mfspr	r10, SPRN_ESR
-	andis.	r10, r10, ESR_ST@h
-	beq	2f
-
-	mfspr	r10, SPRN_DEAR		/* Get faulting address */
-
-	/* If we are faulting a kernel address, we have to use the
-	 * kernel page tables.
-	 */
-	lis	r11, PAGE_OFFSET@h
-	cmplw	r10, r11
-	blt+	3f
-	lis	r11, swapper_pg_dir@h
-	ori	r11, r11, swapper_pg_dir@l
-
-	mfspr   r12,SPRN_MMUCR
-	rlwinm	r12,r12,0,0,23		/* Clear TID */
-
-	b	4f
-
-	/* Get the PGD for the current thread */
-3:
-	mfspr	r11,SPRN_SPRG3
-	lwz	r11,PGDIR(r11)
-
-	/* Load PID into MMUCR TID */
-	mfspr	r12,SPRN_MMUCR		/* Get MMUCR */
-	mfspr   r13,SPRN_PID		/* Get PID */
-	rlwimi	r12,r13,0,24,31		/* Set TID */
-
-4:
-	mtspr   SPRN_MMUCR,r12
-
-	rlwinm  r12, r10, 13, 19, 29    /* Compute pgdir/pmd offset */
-	lwzx    r11, r12, r11           /* Get pgd/pmd entry */
-	rlwinm. r12, r11, 0, 0, 20      /* Extract pt base address */
-	beq     2f                      /* Bail if no table */
-
-	rlwimi  r12, r10, 23, 20, 28    /* Compute pte address */
-	lwz     r11, 4(r12)             /* Get pte entry */
-
-	andi.	r13, r11, _PAGE_RW	/* Is it writeable? */
-	beq	2f			/* Bail if not */
-
-	/* Update 'changed'.
-	*/
-	ori	r11, r11, _PAGE_DIRTY|_PAGE_ACCESSED|_PAGE_HWWRITE
-	stw	r11, 4(r12)		/* Update Linux page table */
-
-	li	r13, PPC44x_TLB_SR@l	/* Set SR */
-	rlwimi	r13, r11, 29, 29, 29	/* SX = _PAGE_HWEXEC */
-	rlwimi	r13, r11, 0, 30, 30	/* SW = _PAGE_RW */
-	rlwimi	r13, r11, 29, 28, 28	/* UR = _PAGE_USER */
-	rlwimi	r12, r11, 31, 26, 26	/* (_PAGE_USER>>1)->r12 */
-	rlwimi	r12, r11, 29, 30, 30	/* (_PAGE_USER>>3)->r12 */
-	and	r12, r12, r11		/* HWEXEC/RW & USER */
-	rlwimi	r13, r12, 0, 26, 26	/* UX = HWEXEC & USER */
-	rlwimi	r13, r12, 3, 27, 27	/* UW = RW & USER */
-
-	rlwimi	r11,r13,0,26,31		/* Insert static perms */
-
-	/*
-	 * Clear U0-U3 and WL1 IL1I IL1D IL2I IL2D bits which are added
-	 * on newer 440 cores like the 440x6 used on AMCC 460EX/460GT (see
-	 * include/asm-powerpc/pgtable-ppc32.h for details).
-	 */
-	rlwinm	r11,r11,0,20,10
-
-	/* find the TLB index that caused the fault.  It has to be here. */
-	tlbsx	r10, 0, r10
-
-	tlbwe	r11, r10, PPC44x_TLB_ATTRIB	/* Write ATTRIB */
-
-	/* Done...restore registers and get out of here.
-	*/
-	mfspr	r11, SPRN_SPRG7R
-	mtcr	r11
-	mfspr	r13, SPRN_SPRG5R
-	mfspr	r12, SPRN_SPRG4R
+	DATA_STORAGE_EXCEPTION
 
-	mfspr	r11, SPRN_SPRG1
-	mfspr	r10, SPRN_SPRG0
-	rfi			/* Force context change */
-
-2:
-	/*
-	 * The bailout.  Restore registers to pre-exception conditions
-	 * and call the heavyweights to help us out.
-	 */
-	mfspr	r11, SPRN_SPRG7R
-	mtcr	r11
-	mfspr	r13, SPRN_SPRG5R
-	mfspr	r12, SPRN_SPRG4R
-
-	mfspr	r11, SPRN_SPRG1
-	mfspr	r10, SPRN_SPRG0
-	b	data_access
-
-	/* Instruction Storage Interrupt */
+		/* Instruction Storage Interrupt */
 	INSTRUCTION_STORAGE_EXCEPTION
 
 	/* External Input Interrupt */
@@ -423,7 +313,6 @@ interrupt_base:
 #else
 	EXCEPTION(0x2010, FloatingPointUnavailable, unknown_exception, EXC_XFER_EE)
 #endif
-
 	/* System Call Interrupt */
 	START_EXCEPTION(SystemCall)
 	NORMAL_EXCEPTION_PROLOG
@@ -484,18 +373,57 @@ interrupt_base:
 4:
 	mtspr	SPRN_MMUCR,r12
 
+	/* Mask of required permission bits. Note that while we
+	 * do copy ESR:ST to _PAGE_RW position as trying to write
+	 * to an RO page is pretty common, we don't do it with
+	 * _PAGE_DIRTY. We could do it, but it's a fairly rare
+	 * event so I'd rather take the overhead when it happens
+	 * rather than adding an instruction here. We should measure
+	 * whether the whole thing is worth it in the first place
+	 * as we could avoid loading SPRN_ESR completely in the first
+	 * place...
+	 *
+	 * TODO: Is it worth doing that mfspr & rlwimi in the first
+	 *       place or can we save a couple of instructions here ?
+	 */
+	mfspr	r12,SPRN_ESR
+	li	r13,_PAGE_PRESENT|_PAGE_ACCESSED
+	rlwimi	r13,r12,10,30,30
+
+	/* Load the PTE */
 	rlwinm 	r12, r10, 13, 19, 29	/* Compute pgdir/pmd offset */
 	lwzx	r11, r12, r11		/* Get pgd/pmd entry */
 	rlwinm.	r12, r11, 0, 0, 20	/* Extract pt base address */
 	beq	2f			/* Bail if no table */
 
 	rlwimi	r12, r10, 23, 20, 28	/* Compute pte address */
-	lwz	r11, 4(r12)		/* Get pte entry */
-	andi.	r13, r11, _PAGE_PRESENT	/* Is the page present? */
-	beq	2f			/* Bail if not present */
+	lwz	r11, 0(r12)		/* Get high word of pte entry */
+	lwz	r12, 4(r12)		/* Get low word of pte entry */
 
-	ori	r11, r11, _PAGE_ACCESSED
-	stw	r11, 4(r12)
+	lis	r10,tlb_44x_index@ha
+
+	andc.	r13,r13,r12		/* Check permission */
+
+	/* Load the next available TLB index */
+	lwz	r13,tlb_44x_index@l(r10)
+
+	bne	2f			/* Bail if permission mismach */
+
+	/* Increment, rollover, and store TLB index */
+	addi	r13,r13,1
+
+	/* Compare with watermark (instruction gets patched) */
+	.globl tlb_44x_patch_hwater_D
+tlb_44x_patch_hwater_D:
+	cmpwi	0,r13,1			/* reserve entries */
+	ble	5f
+	li	r13,0
+5:
+	/* Store the next available TLB index */
+	stw	r13,tlb_44x_index@l(r10)
+
+	/* Re-load the faulting address */
+	mfspr	r10,SPRN_DEAR
 
 	 /* Jump to common tlb load */
 	b	finish_tlb_load
@@ -510,7 +438,7 @@ interrupt_base:
 	mfspr	r12, SPRN_SPRG4R
 	mfspr	r11, SPRN_SPRG1
 	mfspr	r10, SPRN_SPRG0
-	b	data_access
+	b	DataStorage
 
 	/* Instruction TLB Error Interrupt */
 	/*
@@ -554,18 +482,42 @@ interrupt_base:
 4:
 	mtspr	SPRN_MMUCR,r12
 
+	/* Make up the required permissions */
+	li	r13,_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_HWEXEC
+
 	rlwinm	r12, r10, 13, 19, 29	/* Compute pgdir/pmd offset */
 	lwzx	r11, r12, r11		/* Get pgd/pmd entry */
 	rlwinm.	r12, r11, 0, 0, 20	/* Extract pt base address */
 	beq	2f			/* Bail if no table */
 
 	rlwimi	r12, r10, 23, 20, 28	/* Compute pte address */
-	lwz	r11, 4(r12)		/* Get pte entry */
-	andi.	r13, r11, _PAGE_PRESENT	/* Is the page present? */
-	beq	2f			/* Bail if not present */
+	lwz	r11, 0(r12)		/* Get high word of pte entry */
+	lwz	r12, 4(r12)		/* Get low word of pte entry */
 
-	ori	r11, r11, _PAGE_ACCESSED
-	stw	r11, 4(r12)
+	lis	r10,tlb_44x_index@ha
+
+	andc.	r13,r13,r12		/* Check permission */
+
+	/* Load the next available TLB index */
+	lwz	r13,tlb_44x_index@l(r10)
+
+	bne	2f			/* Bail if permission mismach */
+
+	/* Increment, rollover, and store TLB index */
+	addi	r13,r13,1
+
+	/* Compare with watermark (instruction gets patched) */
+	.globl tlb_44x_patch_hwater_I
+tlb_44x_patch_hwater_I:
+	cmpwi	0,r13,1			/* reserve entries */
+	ble	5f
+	li	r13,0
+5:
+	/* Store the next available TLB index */
+	stw	r13,tlb_44x_index@l(r10)
+
+	/* Re-load the faulting address */
+	mfspr	r10,SPRN_SRR0
 
 	/* Jump to common TLB load point */
 	b	finish_tlb_load
@@ -587,86 +539,40 @@ interrupt_base:
 
 /*
  * Local functions
- */
-	/*
-	 * Data TLB exceptions will bail out to this point
-	 * if they can't resolve the lightweight TLB fault.
-	 */
-data_access:
-	NORMAL_EXCEPTION_PROLOG
-	mfspr	r5,SPRN_ESR		/* Grab the ESR, save it, pass arg3 */
-	stw	r5,_ESR(r11)
-	mfspr	r4,SPRN_DEAR		/* Grab the DEAR, save it, pass arg2 */
-	EXC_XFER_EE_LITE(0x0300, handle_page_fault)
+  */
 
 /*
 
  * Both the instruction and data TLB miss get to this
  * point to load the TLB.
  * 	r10 - EA of fault
- * 	r11 - available to use
- *	r12 - Pointer to the 64-bit PTE
- *	r13 - available to use
+ * 	r11 - PTE high word value
+ *	r12 - PTE low word value
+ *	r13 - TLB index
  *	MMUCR - loaded with proper value when we get here
  *	Upon exit, we reload everything and RFI.
  */
 finish_tlb_load:
-	/*
-	 * We set execute, because we don't have the granularity to
-	 * properly set this at the page level (Linux problem).
-	 * If shared is set, we cause a zero PID->TID load.
-	 * Many of these bits are software only.  Bits we don't set
-	 * here we (properly should) assume have the appropriate value.
-	 */
-
-	/* Load the next available TLB index */
-	lis	r13, tlb_44x_index@ha
-	lwz	r13, tlb_44x_index@l(r13)
-	/* Load the TLB high watermark */
-	lis	r11, tlb_44x_hwater@ha
-	lwz	r11, tlb_44x_hwater@l(r11)
-
-	/* Increment, rollover, and store TLB index */
-	addi	r13, r13, 1
-	cmpw	0, r13, r11			/* reserve entries */
-	ble	7f
-	li	r13, 0
-7:
-	/* Store the next available TLB index */
-	lis	r11, tlb_44x_index@ha
-	stw	r13, tlb_44x_index@l(r11)
-
-	lwz	r11, 0(r12)			/* Get MS word of PTE */
-	lwz	r12, 4(r12)			/* Get LS word of PTE */
-	rlwimi	r11, r12, 0, 0 , 19		/* Insert RPN */
-	tlbwe	r11, r13, PPC44x_TLB_XLAT	/* Write XLAT */
+	/* Combine RPN & ERPN an write WS 0 */
+	rlwimi	r11,r12,0,0,19
+	tlbwe	r11,r13,PPC44x_TLB_XLAT
 
 	/*
-	 * Create PAGEID. This is the faulting address,
+	 * Create WS1. This is the faulting address (EPN),
 	 * page size, and valid flag.
 	 */
-	li	r11, PPC44x_TLB_VALID | PPC44x_TLB_4K
-	rlwimi	r10, r11, 0, 20, 31		/* Insert valid and page size */
-	tlbwe	r10, r13, PPC44x_TLB_PAGEID	/* Write PAGEID */
-
-	li	r10, PPC44x_TLB_SR@l		/* Set SR */
-	rlwimi	r10, r12, 0, 30, 30		/* Set SW = _PAGE_RW */
-	rlwimi	r10, r12, 29, 29, 29		/* SX = _PAGE_HWEXEC */
-	rlwimi	r10, r12, 29, 28, 28		/* UR = _PAGE_USER */
-	rlwimi	r11, r12, 31, 26, 26		/* (_PAGE_USER>>1)->r12 */
-	and	r11, r12, r11			/* HWEXEC & USER */
-	rlwimi	r10, r11, 0, 26, 26		/* UX = HWEXEC & USER */
-
-	rlwimi	r12, r10, 0, 26, 31		/* Insert static perms */
-
-	/*
-	 * Clear U0-U3 and WL1 IL1I IL1D IL2I IL2D bits which are added
-	 * on newer 440 cores like the 440x6 used on AMCC 460EX/460GT (see
-	 * include/asm-powerpc/pgtable-ppc32.h for details).
-	 */
-	rlwinm	r12, r12, 0, 20, 10
-
-	tlbwe	r12, r13, PPC44x_TLB_ATTRIB	/* Write ATTRIB */
+	li	r11,PPC44x_TLB_VALID | PPC44x_TLB_4K
+	rlwimi	r10,r11,0,20,31			/* Insert valid and page size*/
+	tlbwe	r10,r13,PPC44x_TLB_PAGEID	/* Write PAGEID */
+
+	/* And WS 2 */
+	li	r10,0xf85			/* Mask to apply from PTE */
+	rlwimi	r10,r12,29,30,30		/* DIRTY -> SW position */
+	and	r11,r12,r10			/* Mask PTE bits to keep */
+	andi.	r10,r12,_PAGE_USER		/* User page ? */
+	beq	1f				/* nope, leave U bits empty */
+	rlwimi	r11,r11,3,26,28			/* yes, copy S bits to U */
+1:	tlbwe	r11,r13,PPC44x_TLB_ATTRIB	/* Write ATTRIB */
 
 	/* Done...restore registers and get out of here.
 	*/