powerpc: Add TLB management code for 64-bit Book3E

This adds the TLB miss handler assembly, the low level TLB flush routines
along with the necessary hook for dealing with our virtual page tables
or indirect TLB entries that need to be flushes when PTE pages are freed.

There is currently no support for hugetlbfs

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 734 insertions, 0 deletions

diff --git a/arch/powerpc/mm/tlb_low_64e.S b/arch/powerpc/mm/tlb_low_64e.S
new file mode 100644
index 000000000000..10d524ded7b2
--- /dev/null
+++ b/arch/powerpc/mm/tlb_low_64e.S
@@ -0,0 +1,734 @@
+/*
+ *  Low leve TLB miss handlers for Book3E
+ *
+ *  Copyright (C) 2008-2009
+ *      Ben. Herrenschmidt (benh@kernel.crashing.org), IBM Corp.
+ *
+ *  This program is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU General Public License
+ *  as published by the Free Software Foundation; either version
+ *  2 of the License, or (at your option) any later version.
+ */
+
+#include <asm/processor.h>
+#include <asm/reg.h>
+#include <asm/page.h>
+#include <asm/mmu.h>
+#include <asm/ppc_asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/cputable.h>
+#include <asm/pgtable.h>
+#include <asm/reg.h>
+#include <asm/exception-64e.h>
+#include <asm/ppc-opcode.h>
+
+#ifdef CONFIG_PPC_64K_PAGES
+#define VPTE_PMD_SHIFT  (PTE_INDEX_SIZE+1)
+#else
+#define VPTE_PMD_SHIFT  (PTE_INDEX_SIZE)
+#endif
+#define VPTE_PUD_SHIFT  (VPTE_PMD_SHIFT + PMD_INDEX_SIZE)
+#define VPTE_PGD_SHIFT  (VPTE_PUD_SHIFT + PUD_INDEX_SIZE)
+#define VPTE_INDEX_SIZE (VPTE_PGD_SHIFT + PGD_INDEX_SIZE)
+
+
+/**********************************************************************
+ *                                                                    *
+ * TLB miss handling for Book3E with TLB reservation and HES support  *
+ *                                                                    *
+ **********************************************************************/
+
+
+/* Data TLB miss */
+        START_EXCEPTION(data_tlb_miss)
+        TLB_MISS_PROLOG
+
+        /* Now we handle the fault proper. We only save DEAR in normal
+         * fault case since that's the only interesting values here.
+         * We could probably also optimize by not saving SRR0/1 in the
+         * linear mapping case but I'll leave that for later
+         */
+        mfspr   r14,SPRN_ESR
+        mfspr   r16,SPRN_DEAR           /* get faulting address */
+        srdi    r15,r16,60              /* get region */
+        cmpldi  cr0,r15,0xc             /* linear mapping ? */
+        TLB_MISS_STATS_SAVE_INFO
+        beq     tlb_load_linear         /* yes -> go to linear map load */
+
+        /* The page tables are mapped virtually linear. At this point, though,
+         * we don't know whether we are trying to fault in a first level
+         * virtual address or a virtual page table address. We can get that
+         * from bit 0x1 of the region ID which we have set for a page table
+         */
+        andi.   r10,r15,0x1
+        bne-    virt_page_table_tlb_miss
+
+        std     r14,EX_TLB_ESR(r12);    /* save ESR */
+        std     r16,EX_TLB_DEAR(r12);   /* save DEAR */
+
+         /* We need _PAGE_PRESENT and  _PAGE_ACCESSED set */
+        li      r11,_PAGE_PRESENT
+        oris    r11,r11,_PAGE_ACCESSED@h
+
+        /* We do the user/kernel test for the PID here along with the RW test
+         */
+        cmpldi  cr0,r15,0               /* Check for user region */
+
+        /* We pre-test some combination of permissions to avoid double
+         * faults:
+         *
+         * We move the ESR:ST bit into the position of _PAGE_BAP_SW in the PTE
+         * ESR_ST   is 0x00800000
+         * _PAGE_BAP_SW is 0x00000010
+         * So the shift is >> 19. This tests for supervisor writeability.
+         * If the page happens to be supervisor writeable and not user
+         * writeable, we will take a new fault later, but that should be
+         * a rare enough case.
+         *
+         * We also move ESR_ST in _PAGE_DIRTY position
+         * _PAGE_DIRTY is 0x00001000 so the shift is >> 11
+         *
+         * MAS1 is preset for all we need except for TID that needs to
+         * be cleared for kernel translations
+         */
+        rlwimi  r11,r14,32-19,27,27
+        rlwimi  r11,r14,32-16,19,19
+        beq     normal_tlb_miss
+        /* XXX replace the RMW cycles with immediate loads + writes */
+1:      mfspr   r10,SPRN_MAS1
+        cmpldi  cr0,r15,8               /* Check for vmalloc region */
+        rlwinm  r10,r10,0,16,1          /* Clear TID */
+        mtspr   SPRN_MAS1,r10
+        beq+    normal_tlb_miss
+
+        /* We got a crappy address, just fault with whatever DEAR and ESR
+         * are here
+         */
+        TLB_MISS_STATS_D(MMSTAT_TLB_MISS_NORM_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_data_storage_book3e
+
+/* Instruction TLB miss */
+        START_EXCEPTION(instruction_tlb_miss)
+        TLB_MISS_PROLOG
+
+        /* If we take a recursive fault, the second level handler may need
+         * to know whether we are handling a data or instruction fault in
+         * order to get to the right store fault handler. We provide that
+         * info by writing a crazy value in ESR in our exception frame
+         */
+        li      r14,-1  /* store to exception frame is done later */
+
+        /* Now we handle the fault proper. We only save DEAR in the non
+         * linear mapping case since we know the linear mapping case will
+         * not re-enter. We could indeed optimize and also not save SRR0/1
+         * in the linear mapping case but I'll leave that for later
+         *
+         * Faulting address is SRR0 which is already in r16
+         */
+        srdi    r15,r16,60              /* get region */
+        cmpldi  cr0,r15,0xc             /* linear mapping ? */
+        TLB_MISS_STATS_SAVE_INFO
+        beq     tlb_load_linear         /* yes -> go to linear map load */
+
+        /* We do the user/kernel test for the PID here along with the RW test
+         */
+        li      r11,_PAGE_PRESENT|_PAGE_HWEXEC  /* Base perm */
+        oris    r11,r11,_PAGE_ACCESSED@h
+
+        cmpldi  cr0,r15,0                       /* Check for user region */
+        std     r14,EX_TLB_ESR(r12)             /* write crazy -1 to frame */
+        beq     normal_tlb_miss
+        /* XXX replace the RMW cycles with immediate loads + writes */
+1:      mfspr   r10,SPRN_MAS1
+        cmpldi  cr0,r15,8                       /* Check for vmalloc region */
+        rlwinm  r10,r10,0,16,1                  /* Clear TID */
+        mtspr   SPRN_MAS1,r10
+        beq+    normal_tlb_miss
+
+        /* We got a crappy address, just fault */
+        TLB_MISS_STATS_I(MMSTAT_TLB_MISS_NORM_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_instruction_storage_book3e
+
+/*
+ * This is the guts of the first-level TLB miss handler for direct
+ * misses. We are entered with:
+ *
+ * r16 = faulting address
+ * r15 = region ID
+ * r14 = crap (free to use)
+ * r13 = PACA
+ * r12 = TLB exception frame in PACA
+ * r11 = PTE permission mask
+ * r10 = crap (free to use)
+ */
+normal_tlb_miss:
+        /* So we first construct the page table address. We do that by
+         * shifting the bottom of the address (not the region ID) by
+         * PAGE_SHIFT-3, clearing the bottom 3 bits (get a PTE ptr) and
+         * or'ing the fourth high bit.
+         *
+         * NOTE: For 64K pages, we do things slightly differently in
+         * order to handle the weird page table format used by linux
+         */
+        ori     r10,r15,0x1
+#ifdef CONFIG_PPC_64K_PAGES
+        /* For the top bits, 16 bytes per PTE */
+        rldicl  r14,r16,64-(PAGE_SHIFT-4),PAGE_SHIFT-4+4
+        /* Now create the bottom bits as 0 in position 0x8000 and
+         * the rest calculated for 8 bytes per PTE
+         */
+        rldicl  r15,r16,64-(PAGE_SHIFT-3),64-15
+        /* Insert the bottom bits in */
+        rlwimi  r14,r15,0,16,31
+#else
+        rldicl  r14,r16,64-(PAGE_SHIFT-3),PAGE_SHIFT-3+4
+#endif
+        sldi    r15,r10,60
+        clrrdi  r14,r14,3
+        or      r10,r15,r14
+
+        /* Set the TLB reservation and seach for existing entry. Then load
+         * the entry.
+         */
+        PPC_TLBSRX_DOT(0,r16)
+        ld      r14,0(r10)
+        beq     normal_tlb_miss_done
+
+finish_normal_tlb_miss:
+        /* Check if required permissions are met */
+        andc.   r15,r11,r14
+        bne-    normal_tlb_miss_access_fault
+
+        /* Now we build the MAS:
+         *
+         * MAS 0   :    Fully setup with defaults in MAS4 and TLBnCFG
+         * MAS 1   :    Almost fully setup
+         *               - PID already updated by caller if necessary
+         *               - TSIZE need change if !base page size, not
+         *                 yet implemented for now
+         * MAS 2   :    Defaults not useful, need to be redone
+         * MAS 3+7 :    Needs to be done
+         *
+         * TODO: mix up code below for better scheduling
+         */
+        clrrdi  r11,r16,12              /* Clear low crap in EA */
+        rlwimi  r11,r14,32-19,27,31     /* Insert WIMGE */
+        mtspr   SPRN_MAS2,r11
+
+        /* Check page size, if not standard, update MAS1 */
+        rldicl  r11,r14,64-8,64-8
+#ifdef CONFIG_PPC_64K_PAGES
+        cmpldi  cr0,r11,BOOK3E_PAGESZ_64K
+#else
+        cmpldi  cr0,r11,BOOK3E_PAGESZ_4K
+#endif
+        beq-    1f
+        mfspr   r11,SPRN_MAS1
+        rlwimi  r11,r14,31,21,24
+        rlwinm  r11,r11,0,21,19
+        mtspr   SPRN_MAS1,r11
+1:
+        /* Move RPN in position */
+        rldicr  r11,r14,64-(PTE_RPN_SHIFT-PAGE_SHIFT),63-PAGE_SHIFT
+        clrldi  r15,r11,12              /* Clear crap at the top */
+        rlwimi  r15,r14,32-8,22,25      /* Move in U bits */
+        rlwimi  r15,r14,32-2,26,31      /* Move in BAP bits */
+
+        /* Mask out SW and UW if !DIRTY (XXX optimize this !) */
+        andi.   r11,r14,_PAGE_DIRTY
+        bne     1f
+        li      r11,MAS3_SW|MAS3_UW
+        andc    r15,r15,r11
+1:      mtspr   SPRN_MAS7_MAS3,r15
+
+        tlbwe
+
+normal_tlb_miss_done:
+        /* We don't bother with restoring DEAR or ESR since we know we are
+         * level 0 and just going back to userland. They are only needed
+         * if you are going to take an access fault
+         */
+        TLB_MISS_STATS_X(MMSTAT_TLB_MISS_NORM_OK)
+        TLB_MISS_EPILOG_SUCCESS
+        rfi
+
+normal_tlb_miss_access_fault:
+        /* We need to check if it was an instruction miss */
+        andi.   r10,r11,_PAGE_HWEXEC
+        bne     1f
+        ld      r14,EX_TLB_DEAR(r12)
+        ld      r15,EX_TLB_ESR(r12)
+        mtspr   SPRN_DEAR,r14
+        mtspr   SPRN_ESR,r15
+        TLB_MISS_STATS_D(MMSTAT_TLB_MISS_NORM_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_data_storage_book3e
+1:      TLB_MISS_STATS_I(MMSTAT_TLB_MISS_NORM_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_instruction_storage_book3e
+
+
+/*
+ * This is the guts of the second-level TLB miss handler for direct
+ * misses. We are entered with:
+ *
+ * r16 = virtual page table faulting address
+ * r15 = region (top 4 bits of address)
+ * r14 = crap (free to use)
+ * r13 = PACA
+ * r12 = TLB exception frame in PACA
+ * r11 = crap (free to use)
+ * r10 = crap (free to use)
+ *
+ * Note that this should only ever be called as a second level handler
+ * with the current scheme when using SW load.
+ * That means we can always get the original fault DEAR at
+ * EX_TLB_DEAR-EX_TLB_SIZE(r12)
+ *
+ * It can be re-entered by the linear mapping miss handler. However, to
+ * avoid too much complication, it will restart the whole fault at level
+ * 0 so we don't care too much about clobbers
+ *
+ * XXX That code was written back when we couldn't clobber r14. We can now,
+ * so we could probably optimize things a bit
+ */
+virt_page_table_tlb_miss:
+        /* Are we hitting a kernel page table ? */
+        andi.   r10,r15,0x8
+
+        /* The cool thing now is that r10 contains 0 for user and 8 for kernel,
+         * and we happen to have the swapper_pg_dir at offset 8 from the user
+         * pgdir in the PACA :-).
+         */
+        add     r11,r10,r13
+
+        /* If kernel, we need to clear MAS1 TID */
+        beq     1f
+        /* XXX replace the RMW cycles with immediate loads + writes */
+        mfspr   r10,SPRN_MAS1
+        rlwinm  r10,r10,0,16,1                  /* Clear TID */
+        mtspr   SPRN_MAS1,r10
+1:
+        /* Search if we already have a TLB entry for that virtual address, and
+         * if we do, bail out.
+         */
+        PPC_TLBSRX_DOT(0,r16)
+        beq     virt_page_table_tlb_miss_done
+
+        /* Now, we need to walk the page tables. First check if we are in
+         * range.
+         */
+        rldicl. r10,r16,64-(VPTE_INDEX_SIZE+3),VPTE_INDEX_SIZE+3+4
+        bne-    virt_page_table_tlb_miss_fault
+
+        /* Get the PGD pointer */
+        ld      r15,PACAPGD(r11)
+        cmpldi  cr0,r15,0
+        beq-    virt_page_table_tlb_miss_fault
+
+        /* Get to PGD entry */
+        rldicl  r11,r16,64-VPTE_PGD_SHIFT,64-PGD_INDEX_SIZE-3
+        clrrdi  r10,r11,3
+        ldx     r15,r10,r15
+        cmpldi  cr0,r15,0
+        beq     virt_page_table_tlb_miss_fault
+
+#ifndef CONFIG_PPC_64K_PAGES
+        /* Get to PUD entry */
+        rldicl  r11,r16,64-VPTE_PUD_SHIFT,64-PUD_INDEX_SIZE-3
+        clrrdi  r10,r11,3
+        ldx     r15,r10,r15
+        cmpldi  cr0,r15,0
+        beq     virt_page_table_tlb_miss_fault
+#endif /* CONFIG_PPC_64K_PAGES */
+
+        /* Get to PMD entry */
+        rldicl  r11,r16,64-VPTE_PMD_SHIFT,64-PMD_INDEX_SIZE-3
+        clrrdi  r10,r11,3
+        ldx     r15,r10,r15
+        cmpldi  cr0,r15,0
+        beq     virt_page_table_tlb_miss_fault
+
+        /* Ok, we're all right, we can now create a kernel translation for
+         * a 4K or 64K page from r16 -> r15.
+         */
+        /* Now we build the MAS:
+         *
+         * MAS 0   :    Fully setup with defaults in MAS4 and TLBnCFG
+         * MAS 1   :    Almost fully setup
+         *               - PID already updated by caller if necessary
+         *               - TSIZE for now is base page size always
+         * MAS 2   :    Use defaults
+         * MAS 3+7 :    Needs to be done
+         *
+         * So we only do MAS 2 and 3 for now...
+         */
+        clrldi  r11,r15,4               /* remove region ID from RPN */
+        ori     r10,r11,1               /* Or-in SR */
+        mtspr   SPRN_MAS7_MAS3,r10
+
+        tlbwe
+
+virt_page_table_tlb_miss_done:
+
+        /* We have overriden MAS2:EPN but currently our primary TLB miss
+         * handler will always restore it so that should not be an issue,
+         * if we ever optimize the primary handler to not write MAS2 on
+         * some cases, we'll have to restore MAS2:EPN here based on the
+         * original fault's DEAR. If we do that we have to modify the
+         * ITLB miss handler to also store SRR0 in the exception frame
+         * as DEAR.
+         *
+         * However, one nasty thing we did is we cleared the reservation
+         * (well, potentially we did). We do a trick here thus if we
+         * are not a level 0 exception (we interrupted the TLB miss) we
+         * offset the return address by -4 in order to replay the tlbsrx
+         * instruction there
+         */
+        subf    r10,r13,r12
+        cmpldi  cr0,r10,PACA_EXTLB+EX_TLB_SIZE
+        bne-    1f
+        ld      r11,PACA_EXTLB+EX_TLB_SIZE+EX_TLB_SRR0(r13)
+        addi    r10,r11,-4
+        std     r10,PACA_EXTLB+EX_TLB_SIZE+EX_TLB_SRR0(r13)
+1:
+        /* Return to caller, normal case */
+        TLB_MISS_STATS_X(MMSTAT_TLB_MISS_PT_OK);
+        TLB_MISS_EPILOG_SUCCESS
+        rfi
+
+virt_page_table_tlb_miss_fault:
+        /* If we fault here, things are a little bit tricky. We need to call
+         * either data or instruction store fault, and we need to retreive
+         * the original fault address and ESR (for data).
+         *
+         * The thing is, we know that in normal circumstances, this is
+         * always called as a second level tlb miss for SW load or as a first
+         * level TLB miss for HW load, so we should be able to peek at the
+         * relevant informations in the first exception frame in the PACA.
+         *
+         * However, we do need to double check that, because we may just hit
+         * a stray kernel pointer or a userland attack trying to hit those
+         * areas. If that is the case, we do a data fault. (We can't get here
+         * from an instruction tlb miss anyway).
+         *
+         * Note also that when going to a fault, we must unwind the previous
+         * level as well. Since we are doing that, we don't need to clear or
+         * restore the TLB reservation neither.
+         */
+        subf    r10,r13,r12
+        cmpldi  cr0,r10,PACA_EXTLB+EX_TLB_SIZE
+        bne-    virt_page_table_tlb_miss_whacko_fault
+
+        /* We dig the original DEAR and ESR from slot 0 */
+        ld      r15,EX_TLB_DEAR+PACA_EXTLB(r13)
+        ld      r16,EX_TLB_ESR+PACA_EXTLB(r13)
+
+        /* We check for the "special" ESR value for instruction faults */
+        cmpdi   cr0,r16,-1
+        beq     1f
+        mtspr   SPRN_DEAR,r15
+        mtspr   SPRN_ESR,r16
+        TLB_MISS_STATS_D(MMSTAT_TLB_MISS_PT_FAULT);
+        TLB_MISS_EPILOG_ERROR
+        b       exc_data_storage_book3e
+1:      TLB_MISS_STATS_I(MMSTAT_TLB_MISS_PT_FAULT);
+        TLB_MISS_EPILOG_ERROR
+        b       exc_instruction_storage_book3e
+
+virt_page_table_tlb_miss_whacko_fault:
+        /* The linear fault will restart everything so ESR and DEAR will
+         * not have been clobbered, let's just fault with what we have
+         */
+        TLB_MISS_STATS_X(MMSTAT_TLB_MISS_PT_FAULT);
+        TLB_MISS_EPILOG_ERROR
+        b       exc_data_storage_book3e
+
+
+/**************************************************************
+ *                                                            *
+ * TLB miss handling for Book3E with hw page table support    *
+ *                                                            *
+ **************************************************************/
+
+
+/* Data TLB miss */
+        START_EXCEPTION(data_tlb_miss_htw)
+        TLB_MISS_PROLOG
+
+        /* Now we handle the fault proper. We only save DEAR in normal
+         * fault case since that's the only interesting values here.
+         * We could probably also optimize by not saving SRR0/1 in the
+         * linear mapping case but I'll leave that for later
+         */
+        mfspr   r14,SPRN_ESR
+        mfspr   r16,SPRN_DEAR           /* get faulting address */
+        srdi    r11,r16,60              /* get region */
+        cmpldi  cr0,r11,0xc             /* linear mapping ? */
+        TLB_MISS_STATS_SAVE_INFO
+        beq     tlb_load_linear         /* yes -> go to linear map load */
+
+        /* We do the user/kernel test for the PID here along with the RW test
+         */
+        cmpldi  cr0,r11,0               /* Check for user region */
+        ld      r15,PACAPGD(r13)        /* Load user pgdir */
+        beq     htw_tlb_miss
+
+        /* XXX replace the RMW cycles with immediate loads + writes */
+1:      mfspr   r10,SPRN_MAS1
+        cmpldi  cr0,r11,8               /* Check for vmalloc region */
+        rlwinm  r10,r10,0,16,1          /* Clear TID */
+        mtspr   SPRN_MAS1,r10
+        ld      r15,PACA_KERNELPGD(r13) /* Load kernel pgdir */
+        beq+    htw_tlb_miss
+
+        /* We got a crappy address, just fault with whatever DEAR and ESR
+         * are here
+         */
+        TLB_MISS_STATS_D(MMSTAT_TLB_MISS_NORM_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_data_storage_book3e
+
+/* Instruction TLB miss */
+        START_EXCEPTION(instruction_tlb_miss_htw)
+        TLB_MISS_PROLOG
+
+        /* If we take a recursive fault, the second level handler may need
+         * to know whether we are handling a data or instruction fault in
+         * order to get to the right store fault handler. We provide that
+         * info by keeping a crazy value for ESR in r14
+         */
+        li      r14,-1  /* store to exception frame is done later */
+
+        /* Now we handle the fault proper. We only save DEAR in the non
+         * linear mapping case since we know the linear mapping case will
+         * not re-enter. We could indeed optimize and also not save SRR0/1
+         * in the linear mapping case but I'll leave that for later
+         *
+         * Faulting address is SRR0 which is already in r16
+         */
+        srdi    r11,r16,60              /* get region */
+        cmpldi  cr0,r11,0xc             /* linear mapping ? */
+        TLB_MISS_STATS_SAVE_INFO
+        beq     tlb_load_linear         /* yes -> go to linear map load */
+
+        /* We do the user/kernel test for the PID here along with the RW test
+         */
+        cmpldi  cr0,r11,0                       /* Check for user region */
+        ld      r15,PACAPGD(r13)                /* Load user pgdir */
+        beq     htw_tlb_miss
+
+        /* XXX replace the RMW cycles with immediate loads + writes */
+1:      mfspr   r10,SPRN_MAS1
+        cmpldi  cr0,r11,8                       /* Check for vmalloc region */
+        rlwinm  r10,r10,0,16,1                  /* Clear TID */
+        mtspr   SPRN_MAS1,r10
+        ld      r15,PACA_KERNELPGD(r13)         /* Load kernel pgdir */
+        beq+    htw_tlb_miss
+
+        /* We got a crappy address, just fault */
+        TLB_MISS_STATS_I(MMSTAT_TLB_MISS_NORM_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_instruction_storage_book3e
+
+
+/*
+ * This is the guts of the second-level TLB miss handler for direct
+ * misses. We are entered with:
+ *
+ * r16 = virtual page table faulting address
+ * r15 = PGD pointer
+ * r14 = ESR
+ * r13 = PACA
+ * r12 = TLB exception frame in PACA
+ * r11 = crap (free to use)
+ * r10 = crap (free to use)
+ *
+ * It can be re-entered by the linear mapping miss handler. However, to
+ * avoid too much complication, it will save/restore things for us
+ */
+htw_tlb_miss:
+        /* Search if we already have a TLB entry for that virtual address, and
+         * if we do, bail out.
+         *
+         * MAS1:IND should be already set based on MAS4
+         */
+        PPC_TLBSRX_DOT(0,r16)
+        beq     htw_tlb_miss_done
+
+        /* Now, we need to walk the page tables. First check if we are in
+         * range.
+         */
+        rldicl. r10,r16,64-PGTABLE_EADDR_SIZE,PGTABLE_EADDR_SIZE+4
+        bne-    htw_tlb_miss_fault
+
+        /* Get the PGD pointer */
+        cmpldi  cr0,r15,0
+        beq-    htw_tlb_miss_fault
+
+        /* Get to PGD entry */
+        rldicl  r11,r16,64-(PGDIR_SHIFT-3),64-PGD_INDEX_SIZE-3
+        clrrdi  r10,r11,3
+        ldx     r15,r10,r15
+        cmpldi  cr0,r15,0
+        beq     htw_tlb_miss_fault
+
+#ifndef CONFIG_PPC_64K_PAGES
+        /* Get to PUD entry */
+        rldicl  r11,r16,64-(PUD_SHIFT-3),64-PUD_INDEX_SIZE-3
+        clrrdi  r10,r11,3
+        ldx     r15,r10,r15
+        cmpldi  cr0,r15,0
+        beq     htw_tlb_miss_fault
+#endif /* CONFIG_PPC_64K_PAGES */
+
+        /* Get to PMD entry */
+        rldicl  r11,r16,64-(PMD_SHIFT-3),64-PMD_INDEX_SIZE-3
+        clrrdi  r10,r11,3
+        ldx     r15,r10,r15
+        cmpldi  cr0,r15,0
+        beq     htw_tlb_miss_fault
+
+        /* Ok, we're all right, we can now create an indirect entry for
+         * a 1M or 256M page.
+         *
+         * The last trick is now that because we use "half" pages for
+         * the HTW (1M IND is 2K and 256M IND is 32K) we need to account
+         * for an added LSB bit to the RPN. For 64K pages, there is no
+         * problem as we already use 32K arrays (half PTE pages), but for
+         * 4K page we need to extract a bit from the virtual address and
+         * insert it into the "PA52" bit of the RPN.
+         */
+#ifndef CONFIG_PPC_64K_PAGES
+        rlwimi  r15,r16,32-9,20,20
+#endif
+        /* Now we build the MAS:
+         *
+         * MAS 0   :    Fully setup with defaults in MAS4 and TLBnCFG
+         * MAS 1   :    Almost fully setup
+         *               - PID already updated by caller if necessary
+         *               - TSIZE for now is base ind page size always
+         * MAS 2   :    Use defaults
+         * MAS 3+7 :    Needs to be done
+         */
+#ifdef CONFIG_PPC_64K_PAGES
+        ori     r10,r15,(BOOK3E_PAGESZ_64K << MAS3_SPSIZE_SHIFT)
+#else
+        ori     r10,r15,(BOOK3E_PAGESZ_4K << MAS3_SPSIZE_SHIFT)
+#endif
+        mtspr   SPRN_MAS7_MAS3,r10
+
+        tlbwe
+
+htw_tlb_miss_done:
+        /* We don't bother with restoring DEAR or ESR since we know we are
+         * level 0 and just going back to userland. They are only needed
+         * if you are going to take an access fault
+         */
+        TLB_MISS_STATS_X(MMSTAT_TLB_MISS_PT_OK)
+        TLB_MISS_EPILOG_SUCCESS
+        rfi
+
+htw_tlb_miss_fault:
+        /* We need to check if it was an instruction miss. We know this
+         * though because r14 would contain -1
+         */
+        cmpdi   cr0,r14,-1
+        beq     1f
+        mtspr   SPRN_DEAR,r16
+        mtspr   SPRN_ESR,r14
+        TLB_MISS_STATS_D(MMSTAT_TLB_MISS_PT_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_data_storage_book3e
+1:      TLB_MISS_STATS_I(MMSTAT_TLB_MISS_PT_FAULT)
+        TLB_MISS_EPILOG_ERROR
+        b       exc_instruction_storage_book3e
+
+/*
+ * This is the guts of "any" level TLB miss handler for kernel linear
+ * mapping misses. We are entered with:
+ *
+ *
+ * r16 = faulting address
+ * r15 = crap (free to use)
+ * r14 = ESR (data) or -1 (instruction)
+ * r13 = PACA
+ * r12 = TLB exception frame in PACA
+ * r11 = crap (free to use)
+ * r10 = crap (free to use)
+ *
+ * In addition we know that we will not re-enter, so in theory, we could
+ * use a simpler epilog not restoring SRR0/1 etc.. but we'll do that later.
+ *
+ * We also need to be careful about MAS registers here & TLB reservation,
+ * as we know we'll have clobbered them if we interrupt the main TLB miss
+ * handlers in which case we probably want to do a full restart at level
+ * 0 rather than saving / restoring the MAS.
+ *
+ * Note: If we care about performance of that core, we can easily shuffle
+ *       a few things around
+ */
+tlb_load_linear:
+        /* For now, we assume the linear mapping is contiguous and stops at
+         * linear_map_top. We also assume the size is a multiple of 1G, thus
+         * we only use 1G pages for now. That might have to be changed in a
+         * final implementation, especially when dealing with hypervisors
+         */
+        ld      r11,PACATOC(r13)
+        ld      r11,linear_map_top@got(r11)
+        ld      r10,0(r11)
+        cmpld   cr0,r10,r16
+        bge     tlb_load_linear_fault
+
+        /* MAS1 need whole new setup. */
+        li      r15,(BOOK3E_PAGESZ_1GB<<MAS1_TSIZE_SHIFT)
+        oris    r15,r15,MAS1_VALID@h    /* MAS1 needs V and TSIZE */
+        mtspr   SPRN_MAS1,r15
+
+        /* Already somebody there ? */
+        PPC_TLBSRX_DOT(0,r16)
+        beq     tlb_load_linear_done
+
+        /* Now we build the remaining MAS. MAS0 and 2 should be fine
+         * with their defaults, which leaves us with MAS 3 and 7. The
+         * mapping is linear, so we just take the address, clear the
+         * region bits, and or in the permission bits which are currently
+         * hard wired
+         */
+        clrrdi  r10,r16,30              /* 1G page index */
+        clrldi  r10,r10,4               /* clear region bits */
+        ori     r10,r10,MAS3_SR|MAS3_SW|MAS3_SX
+        mtspr   SPRN_MAS7_MAS3,r10
+
+        tlbwe
+
+tlb_load_linear_done:
+        /* We use the "error" epilog for success as we do want to
+         * restore to the initial faulting context, whatever it was.
+         * We do that because we can't resume a fault within a TLB
+         * miss handler, due to MAS and TLB reservation being clobbered.
+         */
+        TLB_MISS_STATS_X(MMSTAT_TLB_MISS_LINEAR)
+        TLB_MISS_EPILOG_ERROR
+        rfi
+
+tlb_load_linear_fault:
+        /* We keep the DEAR and ESR around, this shouldn't have happened */
+        cmpdi   cr0,r14,-1
+        beq     1f
+        TLB_MISS_EPILOG_ERROR_SPECIAL
+        b       exc_data_storage_book3e
+1:      TLB_MISS_EPILOG_ERROR_SPECIAL
+        b       exc_instruction_storage_book3e
+
+
+#ifdef CONFIG_BOOK3E_MMU_TLB_STATS
+.tlb_stat_inc:
+1:      ldarx   r8,0,r9
+        addi    r8,r8,1
+        stdcx.  r8,0,r9
+        bne-    1b
+        blr
+#endif