ARC: MMU Exception Handling
* MMU I-TLB / D-TLB Miss Exceptions
- Fast Path TLB Refill Handler
- slowpath TLB creation via do_page_fault() -> update_mmu_cache()
* Duplicate PD Exception Handler
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S
new file mode 100644
index 0000000..fc5b971
--- /dev/null
+++ b/arch/arc/mm/tlbex.S
@@ -0,0 +1,351 @@
+/*
+ * 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/tlb.h>
+#include <asm/pgtable.h>
+#include <asm/arcregs.h>
+#include <asm/cache.h>
+#include <asm/processor.h>
+#if (CONFIG_ARC_MMU_VER == 1)
+#include <asm/tlb-mmu1.h>
+#endif
+
+;--------------------------------------------------------------------------
+; scratch memory to save the registers (r0-r3) used to code TLB refill Handler
+; For details refer to comments before TLBMISS_FREEUP_REGS below
+;--------------------------------------------------------------------------
+
+ .section .data
+ .global ex_saved_reg1
+ .align 1 << L1_CACHE_SHIFT ; IMP: Must be Cache Line aligned
+ .type ex_saved_reg1, @object
+ .size ex_saved_reg1, 16
+ex_saved_reg1:
+ .zero 16
+
+;============================================================================
+; 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 DBG_ASID_MISMATCH
+
+#ifdef CONFIG_ARC_DBG_TLB_PARANOIA
+
+ ; make sure h/w ASID is same as s/w ASID
+
+ GET_CURR_TASK_ON_CPU r3
+ ld r0, [r3, TASK_ACT_MM]
+ ld r0, [r0, MM_CTXT+MM_CTXT_ASID]
+
+ lr r1, [ARC_REG_PID]
+ and r1, r1, 0xFF
+ breq r1, r0, 5f
+
+ ; Error if H/w and S/w ASID don't match, but NOT if in kernel mode
+ lr r0, [erstatus]
+ bbit0 r0, 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 r0, 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]
+
+ lr r1, [ARC_REG_SCRATCH_DATA0] ; current pgd
+
+ 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
+
+.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_IN_PD1 ; Extract permission flags+PFN from PTE
+ sr r3, [ARC_REG_TLBPD1] ; these go in PD1
+
+ and r2, r0, PTE_BITS_IN_PD0 ; Extract other PTE flags: (V)alid, (G)lb
+#if (CONFIG_ARC_MMU_VER <= 2) /* Neednot be done with v3 onwards */
+ lsr r2, r2 ; shift PTE flags to match layout in PD0
+#endif
+
+ 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
+
+;-----------------------------------------------------------------
+; 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]
+
+; As simple as that....
+
+.macro TLBMISS_FREEUP_REGS
+ st r0, [@ex_saved_reg1]
+ mov_s r0, @ex_saved_reg1
+ 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
+
+ DBG_ASID_MISMATCH
+.endm
+
+;-----------------------------------------------------------------
+.macro TLBMISS_RESTORE_REGS
+ 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]
+.endm
+
+.section .text, "ax",@progbits ;Fast Path Code, candidate for ICCM
+
+;-----------------------------------------------------------------------------
+; I-TLB Miss Exception Handler
+;-----------------------------------------------------------------------------
+
+ARC_ENTRY EV_TLBMissI
+
+ TLBMISS_FREEUP_REGS
+
+ ;----------------------------------------------------------------
+ ; Get the PTE corresponding to V-addr accessed
+ LOAD_FAULT_PTE
+
+ ;----------------------------------------------------------------
+ ; VERIFY_PTE: Check if PTE permissions approp for executing code
+ cmp_s r2, VMALLOC_START
+ mov.lo r2, (_PAGE_PRESENT | _PAGE_READ | _PAGE_EXECUTE)
+ mov.hs r2, (_PAGE_PRESENT | _PAGE_K_READ | _PAGE_K_EXECUTE)
+
+ 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_PRESENT | _PAGE_ACCESSED) ; set Accessed Bit
+ st_s r0, [r1] ; Write back PTE
+
+ CONV_PTE_TO_TLB
+ COMMIT_ENTRY_TO_MMU
+ TLBMISS_RESTORE_REGS
+ rtie
+
+ARC_EXIT EV_TLBMissI
+
+;-----------------------------------------------------------------------------
+; D-TLB Miss Exception Handler
+;-----------------------------------------------------------------------------
+
+ARC_ENTRY EV_TLBMissD
+
+ TLBMISS_FREEUP_REGS
+
+ ;----------------------------------------------------------------
+ ; Get the PTE corresponding to V-addr accessed
+ ; If PTE exists, it will setup, r0 = PTE, r1 = Ptr to PTE
+ LOAD_FAULT_PTE
+
+ ;----------------------------------------------------------------
+ ; VERIFY_PTE: Chk if PTE permissions approp for data access (R/W/R+W)
+
+ mov_s r2, 0
+ 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
+ ; which is both Read and Write
+
+ ; If kernel mode access, ; make _PAGE_xx flags as _PAGE_K_xx
+ ; For copy_(to|from)_user, despite exception taken in kernel mode,
+ ; this code is not hit, because EFA would still be the user mode
+ ; address (EFA < 0x6000_0000).
+ ; This code is for legit kernel mode faults, vmalloc specifically
+ ; (EFA: 0x7000_0000 to 0x7FFF_FFFF)
+
+ lr r3, [efa]
+ cmp r3, VMALLOC_START - 1 ; If kernel mode access
+ asl.hi r2, r2, 3 ; make _PAGE_xx flags as _PAGE_K_xx
+ or r2, r2, _PAGE_PRESENT ; Common flag for K/U mode
+
+ ; 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_PRESENT | _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).
+ ; That requires freeing up r9
+ EXCPN_PROLOG_FREEUP_REG r9
+
+ lr r9, [erstatus]
+
+ SWITCH_TO_KERNEL_STK
+ SAVE_ALL_SYS
+
+ ; ------- setup args for Linux Page fault Hanlder ---------
+ mov_s r0, sp
+ lr r2, [efa]
+ lr r3, [ecr]
+
+ ; Both st and ex imply WRITE access of some sort, hence do_page_fault( )
+ ; invoked with write=1 for DTLB-st/ex Miss and write=0 for ITLB miss or
+ ; DTLB-ld Miss
+ ; DTLB Miss Cause code is ld = 0x01 , st = 0x02, ex = 0x03
+ ; Following code uses that fact that st/ex have one bit in common
+
+ btst_s r3, ECR_C_BIT_DTLB_ST_MISS
+ mov.z r1, 0
+ mov.nz r1, 1
+
+ ; 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
+
+ARC_EXIT EV_TLBMissD
+
+ARC_ENTRY EV_TLBMissB ; Bogus entry to measure sz of DTLBMiss hdlr