/* * 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 #include #include #include #include #include #include #include ;----------------------------------------------------------------- ; 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)