/* $Id$ * dtlb_backend.S: Back end to DTLB miss replacement strategy. * This is included directly into the trap table. * * Copyright (C) 1996,1998 David S. Miller (davem@redhat.com) * Copyright (C) 1997,1998 Jakub Jelinek (jj@ultra.linux.cz) */ #include #include #define VALID_SZ_BITS (_PAGE_VALID | _PAGE_SZBITS) #define VPTE_BITS (_PAGE_CP | _PAGE_CV | _PAGE_P ) #define VPTE_SHIFT (PAGE_SHIFT - 3) /* Ways we can get here: * * 1) Nucleus loads and stores to/from PA-->VA direct mappings at tl>1. * 2) Nucleus loads and stores to/from user/kernel window save areas. * 3) VPTE misses from dtlb_base and itlb_base. * * We need to extract out the PMD and PGDIR indexes from the * linear virtual page table access address. The PTE index * is at the bottom, but we are not concerned with it. Bits * 0 to 2 are clear since each PTE is 8 bytes in size. Each * PMD and PGDIR entry are 4 bytes in size. Thus, this * address looks something like: * * |---------------------------------------------------------------| * | ... | PGDIR index | PMD index | PTE index | | * |---------------------------------------------------------------| * 63 F E D C B A 3 2 0 <- bit nr * * The variable bits above are defined as: * A --> 3 + (PAGE_SHIFT - log2(8)) * --> 3 + (PAGE_SHIFT - 3) - 1 * (ie. this is "bit 3" + PAGE_SIZE - size of PTE entry in bits - 1) * B --> A + 1 * C --> B + (PAGE_SHIFT - log2(4)) * --> B + (PAGE_SHIFT - 2) - 1 * (ie. this is "bit B" + PAGE_SIZE - size of PMD entry in bits - 1) * D --> C + 1 * E --> D + (PAGE_SHIFT - log2(4)) * --> D + (PAGE_SHIFT - 2) - 1 * (ie. this is "bit D" + PAGE_SIZE - size of PGDIR entry in bits - 1) * F --> E + 1 * * (Note how "B" always evalutes to PAGE_SHIFT, all the other constants * cancel out.) * * For 8K PAGE_SIZE (thus, PAGE_SHIFT of 13) the bit numbers are: * A --> 12 * B --> 13 * C --> 23 * D --> 24 * E --> 34 * F --> 35 * * For 64K PAGE_SIZE (thus, PAGE_SHIFT of 16) the bit numbers are: * A --> 15 * B --> 16 * C --> 29 * D --> 30 * E --> 43 * F --> 44 * * Because bits both above and below each PGDIR and PMD index need to * be masked out, and the index can be as long as 14 bits (when using a * 64K PAGE_SIZE, and thus a PAGE_SHIFT of 16), we need 3 instructions * to extract each index out. * * Shifts do not pair very well on UltraSPARC-I, II, IIi, and IIe, so * we try to avoid using them for the entire operation. We could setup * a mask anywhere from bit 31 down to bit 10 using the sethi instruction. * * We need a mask covering bits B --> C and one covering D --> E. * For 8K PAGE_SIZE these masks are 0x00ffe000 and 0x7ff000000. * For 64K PAGE_SIZE these masks are 0x3fff0000 and 0xfffc0000000. * The second in each set cannot be loaded with a single sethi * instruction, because the upper bits are past bit 32. We would * need to use a sethi + a shift. * * For the time being, we use 2 shifts and a simple "and" mask. * We shift left to clear the bits above the index, we shift down * to clear the bits below the index (sans the log2(4 or 8) bits) * and a mask to clear the log2(4 or 8) bits. We need therefore * define 4 shift counts, all of which are relative to PAGE_SHIFT. * * Although unsupportable for other reasons, this does mean that * 512K and 4MB page sizes would be generaally supported by the * kernel. (ELF binaries would break with > 64K PAGE_SIZE since * the sections are only aligned that strongly). * * The operations performed for extraction are thus: * * ((X << FOO_SHIFT_LEFT) >> FOO_SHIFT_RIGHT) & ~0x3 * */ #define A (3 + (PAGE_SHIFT - 3) - 1) #define B (A + 1) #define C (B + (PAGE_SHIFT - 2) - 1) #define D (C + 1) #define E (D + (PAGE_SHIFT - 2) - 1) #define F (E + 1) #define PMD_SHIFT_LEFT (64 - D) #define PMD_SHIFT_RIGHT (64 - (D - B) - 2) #define PGDIR_SHIFT_LEFT (64 - F) #define PGDIR_SHIFT_RIGHT (64 - (F - D) - 2) #define LOW_MASK_BITS 0x3 /* TLB1 ** ICACHE line 1: tl1 DTLB and quick VPTE miss */ ldxa [%g1 + %g1] ASI_DMMU, %g4 ! Get TAG_ACCESS add %g3, %g3, %g5 ! Compute VPTE base cmp %g4, %g5 ! VPTE miss? bgeu,pt %xcc, 1f ! Continue here andcc %g4, TAG_CONTEXT_BITS, %g5 ! tl0 miss Nucleus test ba,a,pt %xcc, from_tl1_trap ! Fall to tl0 miss 1: sllx %g6, VPTE_SHIFT, %g4 ! Position TAG_ACCESS or %g4, %g5, %g4 ! Prepare TAG_ACCESS /* TLB1 ** ICACHE line 2: Quick VPTE miss */ mov TSB_REG, %g1 ! Grab TSB reg ldxa [%g1] ASI_DMMU, %g5 ! Doing PGD caching? sllx %g6, PMD_SHIFT_LEFT, %g1 ! Position PMD offset be,pn %xcc, sparc64_vpte_nucleus ! Is it from Nucleus? srlx %g1, PMD_SHIFT_RIGHT, %g1 ! Mask PMD offset bits brnz,pt %g5, sparc64_vpte_continue ! Yep, go like smoke andn %g1, LOW_MASK_BITS, %g1 ! Final PMD mask sllx %g6, PGDIR_SHIFT_LEFT, %g5 ! Position PGD offset /* TLB1 ** ICACHE line 3: Quick VPTE miss */ srlx %g5, PGDIR_SHIFT_RIGHT, %g5 ! Mask PGD offset bits andn %g5, LOW_MASK_BITS, %g5 ! Final PGD mask lduwa [%g7 + %g5] ASI_PHYS_USE_EC, %g5! Load PGD brz,pn %g5, vpte_noent ! Valid? sparc64_kpte_continue: sllx %g5, 11, %g5 ! Shift into place sparc64_vpte_continue: lduwa [%g5 + %g1] ASI_PHYS_USE_EC, %g5! Load PMD sllx %g5, 11, %g5 ! Shift into place brz,pn %g5, vpte_noent ! Valid? /* TLB1 ** ICACHE line 4: Quick VPTE miss */ mov (VALID_SZ_BITS >> 61), %g1 ! upper vpte into %g1 sllx %g1, 61, %g1 ! finish calc or %g5, VPTE_BITS, %g5 ! Prepare VPTE data or %g5, %g1, %g5 ! ... mov TLB_SFSR, %g1 ! Restore %g1 value stxa %g5, [%g0] ASI_DTLB_DATA_IN ! Load VPTE into TLB stxa %g4, [%g1 + %g1] ASI_DMMU ! Restore previous TAG_ACCESS retry ! Load PTE once again #undef VALID_SZ_BITS #undef VPTE_SHIFT #undef VPTE_BITS #undef A #undef B #undef C #undef D #undef E #undef F #undef PMD_SHIFT_LEFT #undef PMD_SHIFT_RIGHT #undef PGDIR_SHIFT_LEFT #undef PGDIR_SHIFT_RIGHT #undef LOW_MASK_BITS