diff options
Diffstat (limited to 'include/asm-ppc/mmu_context.h')
| -rw-r--r-- | include/asm-ppc/mmu_context.h | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/include/asm-ppc/mmu_context.h b/include/asm-ppc/mmu_context.h new file mode 100644 index 000000000000..9222fa6ca172 --- /dev/null +++ b/include/asm-ppc/mmu_context.h @@ -0,0 +1,197 @@ +#ifdef __KERNEL__ +#ifndef __PPC_MMU_CONTEXT_H +#define __PPC_MMU_CONTEXT_H + +#include <linux/config.h> +#include <asm/atomic.h> +#include <asm/bitops.h> +#include <asm/mmu.h> +#include <asm/cputable.h> + +/* + * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs + * (virtual segment identifiers) for each context. Although the + * hardware supports 24-bit VSIDs, and thus >1 million contexts, + * we only use 32,768 of them. That is ample, since there can be + * at most around 30,000 tasks in the system anyway, and it means + * that we can use a bitmap to indicate which contexts are in use. + * Using a bitmap means that we entirely avoid all of the problems + * that we used to have when the context number overflowed, + * particularly on SMP systems. + * -- paulus. + */ + +/* + * This function defines the mapping from contexts to VSIDs (virtual + * segment IDs). We use a skew on both the context and the high 4 bits + * of the 32-bit virtual address (the "effective segment ID") in order + * to spread out the entries in the MMU hash table. Note, if this + * function is changed then arch/ppc/mm/hashtable.S will have to be + * changed to correspond. + */ +#define CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \ + & 0xffffff) + +/* + The MPC8xx has only 16 contexts. We rotate through them on each + task switch. A better way would be to keep track of tasks that + own contexts, and implement an LRU usage. That way very active + tasks don't always have to pay the TLB reload overhead. The + kernel pages are mapped shared, so the kernel can run on behalf + of any task that makes a kernel entry. Shared does not mean they + are not protected, just that the ASID comparison is not performed. + -- Dan + + The IBM4xx has 256 contexts, so we can just rotate through these + as a way of "switching" contexts. If the TID of the TLB is zero, + the PID/TID comparison is disabled, so we can use a TID of zero + to represent all kernel pages as shared among all contexts. + -- Dan + */ + +static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) +{ +} + +#ifdef CONFIG_8xx +#define NO_CONTEXT 16 +#define LAST_CONTEXT 15 +#define FIRST_CONTEXT 0 + +#elif defined(CONFIG_4xx) +#define NO_CONTEXT 256 +#define LAST_CONTEXT 255 +#define FIRST_CONTEXT 1 + +#elif defined(CONFIG_E500) +#define NO_CONTEXT 256 +#define LAST_CONTEXT 255 +#define FIRST_CONTEXT 1 + +#else + +/* PPC 6xx, 7xx CPUs */ +#define NO_CONTEXT ((mm_context_t) -1) +#define LAST_CONTEXT 32767 +#define FIRST_CONTEXT 1 +#endif + +/* + * Set the current MMU context. + * On 32-bit PowerPCs (other than the 8xx embedded chips), this is done by + * loading up the segment registers for the user part of the address space. + * + * Since the PGD is immediately available, it is much faster to simply + * pass this along as a second parameter, which is required for 8xx and + * can be used for debugging on all processors (if you happen to have + * an Abatron). + */ +extern void set_context(mm_context_t context, pgd_t *pgd); + +/* + * Bitmap of contexts in use. + * The size of this bitmap is LAST_CONTEXT + 1 bits. + */ +extern unsigned long context_map[]; + +/* + * This caches the next context number that we expect to be free. + * Its use is an optimization only, we can't rely on this context + * number to be free, but it usually will be. + */ +extern mm_context_t next_mmu_context; + +/* + * If we don't have sufficient contexts to give one to every task + * that could be in the system, we need to be able to steal contexts. + * These variables support that. + */ +#if LAST_CONTEXT < 30000 +#define FEW_CONTEXTS 1 +extern atomic_t nr_free_contexts; +extern struct mm_struct *context_mm[LAST_CONTEXT+1]; +extern void steal_context(void); +#endif + +/* + * Get a new mmu context for the address space described by `mm'. + */ +static inline void get_mmu_context(struct mm_struct *mm) +{ + mm_context_t ctx; + + if (mm->context != NO_CONTEXT) + return; +#ifdef FEW_CONTEXTS + while (atomic_dec_if_positive(&nr_free_contexts) < 0) + steal_context(); +#endif + ctx = next_mmu_context; + while (test_and_set_bit(ctx, context_map)) { + ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx); + if (ctx > LAST_CONTEXT) + ctx = 0; + } + next_mmu_context = (ctx + 1) & LAST_CONTEXT; + mm->context = ctx; +#ifdef FEW_CONTEXTS + context_mm[ctx] = mm; +#endif +} + +/* + * Set up the context for a new address space. + */ +#define init_new_context(tsk,mm) (((mm)->context = NO_CONTEXT), 0) + +/* + * We're finished using the context for an address space. + */ +static inline void destroy_context(struct mm_struct *mm) +{ + if (mm->context != NO_CONTEXT) { + clear_bit(mm->context, context_map); + mm->context = NO_CONTEXT; +#ifdef FEW_CONTEXTS + atomic_inc(&nr_free_contexts); +#endif + } +} + +static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, + struct task_struct *tsk) +{ +#ifdef CONFIG_ALTIVEC + asm volatile ( + BEGIN_FTR_SECTION + "dssall;\n" +#ifndef CONFIG_POWER4 + "sync;\n" /* G4 needs a sync here, G5 apparently not */ +#endif + END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC) + : : ); +#endif /* CONFIG_ALTIVEC */ + + tsk->thread.pgdir = next->pgd; + + /* No need to flush userspace segments if the mm doesnt change */ + if (prev == next) + return; + + /* Setup new userspace context */ + get_mmu_context(next); + set_context(next->context, next->pgd); +} + +#define deactivate_mm(tsk,mm) do { } while (0) + +/* + * After we have set current->mm to a new value, this activates + * the context for the new mm so we see the new mappings. + */ +#define activate_mm(active_mm, mm) switch_mm(active_mm, mm, current) + +extern void mmu_context_init(void); + +#endif /* __PPC_MMU_CONTEXT_H */ +#endif /* __KERNEL__ */ |