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+/*
+ * TLB Exception Handling for ARC
+ *
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Vineetg: April 2011 :
+ * -MMU v1: moved out legacy code into a seperate file
+ * -MMU v3: PD{0,1} bits layout changed: They don't overlap anymore,
+ * helps avoid a shift when preparing PD0 from PTE
+ *
+ * Vineetg: July 2009
+ * -For MMU V2, we need not do heuristics at the time of commiting a D-TLB
+ * entry, so that it doesn't knock out it's I-TLB entry
+ * -Some more fine tuning:
+ * bmsk instead of add, asl.cc instead of branch, delay slot utilise etc
+ *
+ * Vineetg: July 2009
+ * -Practically rewrote the I/D TLB Miss handlers
+ * Now 40 and 135 instructions a peice as compared to 131 and 449 resp.
+ * Hence Leaner by 1.5 K
+ * Used Conditional arithmetic to replace excessive branching
+ * Also used short instructions wherever possible
+ *
+ * Vineetg: Aug 13th 2008
+ * -Passing ECR (Exception Cause REG) to do_page_fault( ) for printing
+ * more information in case of a Fatality
+ *
+ * Vineetg: March 25th Bug #92690
+ * -Added Debug Code to check if sw-ASID == hw-ASID
+
+ * Rahul Trivedi, Amit Bhor: Codito Technologies 2004
+ */
+
+ .cpu A7
+
+#include <linux/linkage.h>
+#include <asm/entry.h>
+#include <asm/mmu.h>
+#include <asm/pgtable.h>
+#include <asm/arcregs.h>
+#include <asm/cache.h>
+#include <asm/processor.h>
+#include <asm/tlb-mmu1.h>
+
+;-----------------------------------------------------------------
+; ARC700 Exception Handling doesn't auto-switch stack and it only provides
+; ONE scratch AUX reg "ARC_REG_SCRATCH_DATA0"
+;
+; For Non-SMP, the scratch AUX reg is repurposed to cache task PGD, so a
+; "global" is used to free-up FIRST core reg to be able to code the rest of
+; exception prologue (IRQ auto-disabled on Exceptions, so it's IRQ-safe).
+; Since the Fast Path TLB Miss handler is coded with 4 regs, the remaining 3
+; need to be saved as well by extending the "global" to be 4 words. Hence
+; ".size ex_saved_reg1, 16"
+; [All of this dance is to avoid stack switching for each TLB Miss, since we
+; only need to save only a handful of regs, as opposed to complete reg file]
+;
+; For ARC700 SMP, the "global" obviously can't be used for free up the FIRST
+; core reg as it will not be SMP safe.
+; Thus scratch AUX reg is used (and no longer used to cache task PGD).
+; To save the rest of 3 regs - per cpu, the global is made "per-cpu".
+; Epilogue thus has to locate the "per-cpu" storage for regs.
+; To avoid cache line bouncing the per-cpu global is aligned/sized per
+; L1_CACHE_SHIFT, despite fundamentally needing to be 12 bytes only. Hence
+; ".size ex_saved_reg1, (CONFIG_NR_CPUS << L1_CACHE_SHIFT)"
+
+; As simple as that....
+;--------------------------------------------------------------------------
+
+; scratch memory to save [r0-r3] used to code TLB refill Handler
+ARCFP_DATA ex_saved_reg1
+ .align 1 << L1_CACHE_SHIFT
+ .type ex_saved_reg1, @object
+#ifdef CONFIG_SMP
+ .size ex_saved_reg1, (CONFIG_NR_CPUS << L1_CACHE_SHIFT)
+ex_saved_reg1:
+ .zero (CONFIG_NR_CPUS << L1_CACHE_SHIFT)
+#else
+ .size ex_saved_reg1, 16
+ex_saved_reg1:
+ .zero 16
+#endif
+
+.macro TLBMISS_FREEUP_REGS
+#ifdef CONFIG_SMP
+ sr r0, [ARC_REG_SCRATCH_DATA0] ; freeup r0 to code with
+ GET_CPU_ID r0 ; get to per cpu scratch mem,
+ lsl r0, r0, L1_CACHE_SHIFT ; cache line wide per cpu
+ add r0, @ex_saved_reg1, r0
+#else
+ st r0, [@ex_saved_reg1]
+ mov_s r0, @ex_saved_reg1
+#endif
+ st_s r1, [r0, 4]
+ st_s r2, [r0, 8]
+ st_s r3, [r0, 12]
+
+ ; VERIFY if the ASID in MMU-PID Reg is same as
+ ; one in Linux data structures
+
+ tlb_paranoid_check_asm
+.endm
+
+.macro TLBMISS_RESTORE_REGS
+#ifdef CONFIG_SMP
+ GET_CPU_ID r0 ; get to per cpu scratch mem
+ lsl r0, r0, L1_CACHE_SHIFT ; each is cache line wide
+ add r0, @ex_saved_reg1, r0
+ ld_s r3, [r0,12]
+ ld_s r2, [r0, 8]
+ ld_s r1, [r0, 4]
+ lr r0, [ARC_REG_SCRATCH_DATA0]
+#else
+ mov_s r0, @ex_saved_reg1
+ ld_s r3, [r0,12]
+ ld_s r2, [r0, 8]
+ ld_s r1, [r0, 4]
+ ld_s r0, [r0]
+#endif
+.endm
+
+;============================================================================
+; Troubleshooting Stuff
+;============================================================================
+
+; Linux keeps ASID (Address Space ID) in task->active_mm->context.asid
+; When Creating TLB Entries, instead of doing 3 dependent loads from memory,
+; we use the MMU PID Reg to get current ASID.
+; In bizzare scenrios SW and HW ASID can get out-of-sync which is trouble.
+; So we try to detect this in TLB Mis shandler
+
+.macro tlb_paranoid_check_asm
+
+#ifdef CONFIG_ARC_DBG_TLB_PARANOIA
+
+ GET_CURR_TASK_ON_CPU r3
+ ld r0, [r3, TASK_ACT_MM]
+ ld r0, [r0, MM_CTXT+MM_CTXT_ASID]
+ breq r0, 0, 55f ; Error if no ASID allocated
+
+ lr r1, [ARC_REG_PID]
+ and r1, r1, 0xFF
+
+ and r2, r0, 0xFF ; MMU PID bits only for comparison
+ breq r1, r2, 5f
+
+55:
+ ; Error if H/w and S/w ASID don't match, but NOT if in kernel mode
+ lr r2, [erstatus]
+ bbit0 r2, STATUS_U_BIT, 5f
+
+ ; We sure are in troubled waters, Flag the error, but to do so
+ ; need to switch to kernel mode stack to call error routine
+ GET_TSK_STACK_BASE r3, sp
+
+ ; Call printk to shoutout aloud
+ mov r2, 1
+ j print_asid_mismatch
+
+5: ; ASIDs match so proceed normally
+ nop
+
+#endif
+
+.endm
+
+;============================================================================
+;TLB Miss handling Code
+;============================================================================
+
+;-----------------------------------------------------------------------------
+; This macro does the page-table lookup for the faulting address.
+; OUT: r0 = PTE faulted on, r1 = ptr to PTE, r2 = Faulting V-address
+.macro LOAD_FAULT_PTE
+
+ lr r2, [efa]
+
+#ifndef CONFIG_SMP
+ lr r1, [ARC_REG_SCRATCH_DATA0] ; current pgd
+#else
+ GET_CURR_TASK_ON_CPU r1
+ ld r1, [r1, TASK_ACT_MM]
+ ld r1, [r1, MM_PGD]
+#endif
+
+ lsr r0, r2, PGDIR_SHIFT ; Bits for indexing into PGD
+ ld.as r1, [r1, r0] ; PGD entry corresp to faulting addr
+ and.f r1, r1, PAGE_MASK ; Ignoring protection and other flags
+ ; contains Ptr to Page Table
+ bz.d do_slow_path_pf ; if no Page Table, do page fault
+
+ ; Get the PTE entry: The idea is
+ ; (1) x = addr >> PAGE_SHIFT -> masks page-off bits from @fault-addr
+ ; (2) y = x & (PTRS_PER_PTE - 1) -> to get index
+ ; (3) z = pgtbl[y]
+ ; To avoid the multiply by in end, we do the -2, <<2 below
+
+ lsr r0, r2, (PAGE_SHIFT - 2)
+ and r0, r0, ( (PTRS_PER_PTE - 1) << 2)
+ ld.aw r0, [r1, r0] ; get PTE and PTE ptr for fault addr
+#ifdef CONFIG_ARC_DBG_TLB_MISS_COUNT
+ and.f 0, r0, _PAGE_PRESENT
+ bz 1f
+ ld r3, [num_pte_not_present]
+ add r3, r3, 1
+ st r3, [num_pte_not_present]
+1:
+#endif
+
+.endm
+
+;-----------------------------------------------------------------
+; Convert Linux PTE entry into TLB entry
+; A one-word PTE entry is programmed as two-word TLB Entry [PD0:PD1] in mmu
+; IN: r0 = PTE, r1 = ptr to PTE
+
+.macro CONV_PTE_TO_TLB
+ and r3, r0, PTE_BITS_RWX ; r w x
+ lsl r2, r3, 3 ; r w x 0 0 0 (GLOBAL, kernel only)
+ and.f 0, r0, _PAGE_GLOBAL
+ or.z r2, r2, r3 ; r w x r w x (!GLOBAL, user page)
+
+ and r3, r0, PTE_BITS_NON_RWX_IN_PD1 ; Extract PFN+cache bits from PTE
+ or r3, r3, r2
+
+ sr r3, [ARC_REG_TLBPD1] ; these go in PD1
+
+ and r2, r0, PTE_BITS_IN_PD0 ; Extract other PTE flags: (V)alid, (G)lb
+
+ lr r3,[ARC_REG_TLBPD0] ; MMU prepares PD0 with vaddr and asid
+
+ or r3, r3, r2 ; S | vaddr | {sasid|asid}
+ sr r3,[ARC_REG_TLBPD0] ; rewrite PD0
+.endm
+
+;-----------------------------------------------------------------
+; Commit the TLB entry into MMU
+
+.macro COMMIT_ENTRY_TO_MMU
+
+ /* Get free TLB slot: Set = computed from vaddr, way = random */
+ sr TLBGetIndex, [ARC_REG_TLBCOMMAND]
+
+ /* Commit the Write */
+#if (CONFIG_ARC_MMU_VER >= 2) /* introduced in v2 */
+ sr TLBWriteNI, [ARC_REG_TLBCOMMAND]
+#else
+ sr TLBWrite, [ARC_REG_TLBCOMMAND]
+#endif
+.endm
+
+
+ARCFP_CODE ;Fast Path Code, candidate for ICCM
+
+;-----------------------------------------------------------------------------
+; I-TLB Miss Exception Handler
+;-----------------------------------------------------------------------------
+
+ENTRY(EV_TLBMissI)
+
+ TLBMISS_FREEUP_REGS
+
+#ifdef CONFIG_ARC_DBG_TLB_MISS_COUNT
+ ld r0, [@numitlb]
+ add r0, r0, 1
+ st r0, [@numitlb]
+#endif
+
+ ;----------------------------------------------------------------
+ ; Get the PTE corresponding to V-addr accessed, r2 is setup with EFA
+ LOAD_FAULT_PTE
+
+ ;----------------------------------------------------------------
+ ; VERIFY_PTE: Check if PTE permissions approp for executing code
+ cmp_s r2, VMALLOC_START
+ mov_s r2, (_PAGE_PRESENT | _PAGE_EXECUTE)
+ or.hs r2, r2, _PAGE_GLOBAL
+
+ and r3, r0, r2 ; Mask out NON Flag bits from PTE
+ xor.f r3, r3, r2 ; check ( ( pte & flags_test ) == flags_test )
+ bnz do_slow_path_pf
+
+ ; Let Linux VM know that the page was accessed
+ or r0, r0, _PAGE_ACCESSED ; set Accessed Bit
+ st_s r0, [r1] ; Write back PTE
+
+ CONV_PTE_TO_TLB
+ COMMIT_ENTRY_TO_MMU
+ TLBMISS_RESTORE_REGS
+ rtie
+
+END(EV_TLBMissI)
+
+;-----------------------------------------------------------------------------
+; D-TLB Miss Exception Handler
+;-----------------------------------------------------------------------------
+
+ENTRY(EV_TLBMissD)
+
+ TLBMISS_FREEUP_REGS
+
+#ifdef CONFIG_ARC_DBG_TLB_MISS_COUNT
+ ld r0, [@numdtlb]
+ add r0, r0, 1
+ st r0, [@numdtlb]
+#endif
+
+ ;----------------------------------------------------------------
+ ; Get the PTE corresponding to V-addr accessed
+ ; If PTE exists, it will setup, r0 = PTE, r1 = Ptr to PTE, r2 = EFA
+ LOAD_FAULT_PTE
+
+ ;----------------------------------------------------------------
+ ; VERIFY_PTE: Chk if PTE permissions approp for data access (R/W/R+W)
+
+ cmp_s r2, VMALLOC_START
+ mov_s r2, _PAGE_PRESENT ; common bit for K/U PTE
+ or.hs r2, r2, _PAGE_GLOBAL ; kernel PTE only
+
+ ; Linux PTE [RWX] bits are semantically overloaded:
+ ; -If PAGE_GLOBAL set, they refer to kernel-only flags (vmalloc)
+ ; -Otherwise they are user-mode permissions, and those are exactly
+ ; same for kernel mode as well (e.g. copy_(to|from)_user)
+
+ lr r3, [ecr]
+ btst_s r3, ECR_C_BIT_DTLB_LD_MISS ; Read Access
+ or.nz r2, r2, _PAGE_READ ; chk for Read flag in PTE
+ btst_s r3, ECR_C_BIT_DTLB_ST_MISS ; Write Access
+ or.nz r2, r2, _PAGE_WRITE ; chk for Write flag in PTE
+ ; Above laddering takes care of XCHG access (both R and W)
+
+ ; By now, r2 setup with all the Flags we need to check in PTE
+ and r3, r0, r2 ; Mask out NON Flag bits from PTE
+ brne.d r3, r2, do_slow_path_pf ; is ((pte & flags_test) == flags_test)
+
+ ;----------------------------------------------------------------
+ ; UPDATE_PTE: Let Linux VM know that page was accessed/dirty
+ lr r3, [ecr]
+ or r0, r0, _PAGE_ACCESSED ; Accessed bit always
+ btst_s r3, ECR_C_BIT_DTLB_ST_MISS ; See if it was a Write Access ?
+ or.nz r0, r0, _PAGE_MODIFIED ; if Write, set Dirty bit as well
+ st_s r0, [r1] ; Write back PTE
+
+ CONV_PTE_TO_TLB
+
+#if (CONFIG_ARC_MMU_VER == 1)
+ ; MMU with 2 way set assoc J-TLB, needs some help in pathetic case of
+ ; memcpy where 3 parties contend for 2 ways, ensuing a livelock.
+ ; But only for old MMU or one with Metal Fix
+ TLB_WRITE_HEURISTICS
+#endif
+
+ COMMIT_ENTRY_TO_MMU
+ TLBMISS_RESTORE_REGS
+ rtie
+
+;-------- Common routine to call Linux Page Fault Handler -----------
+do_slow_path_pf:
+
+ ; Restore the 4-scratch regs saved by fast path miss handler
+ TLBMISS_RESTORE_REGS
+
+ ; Slow path TLB Miss handled as a regular ARC Exception
+ ; (stack switching / save the complete reg-file).
+ EXCEPTION_PROLOGUE
+
+ ; ------- setup args for Linux Page fault Hanlder ---------
+ mov_s r1, sp
+ lr r0, [efa]
+
+ ; We don't want exceptions to be disabled while the fault is handled.
+ ; Now that we have saved the context we return from exception hence
+ ; exceptions get re-enable
+
+ FAKE_RET_FROM_EXCPN r9
+
+ bl do_page_fault
+ b ret_from_exception
+
+END(EV_TLBMissD)