diff options
Diffstat (limited to 'arch/riscv/mm/context.c')
| -rw-r--r-- | arch/riscv/mm/context.c | 291 |
1 files changed, 281 insertions, 10 deletions
diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c index 613ec81a8979..ba8eb3944687 100644 --- a/arch/riscv/mm/context.c +++ b/arch/riscv/mm/context.c @@ -2,13 +2,287 @@ /* * Copyright (C) 2012 Regents of the University of California * Copyright (C) 2017 SiFive + * Copyright (C) 2021 Western Digital Corporation or its affiliates. */ +#include <linux/bitops.h> +#include <linux/cpumask.h> #include <linux/mm.h> +#include <linux/percpu.h> +#include <linux/slab.h> +#include <linux/spinlock.h> +#include <linux/static_key.h> #include <asm/tlbflush.h> #include <asm/cacheflush.h> #include <asm/mmu_context.h> +#ifdef CONFIG_MMU + +DEFINE_STATIC_KEY_FALSE(use_asid_allocator); + +static unsigned long asid_bits; +static unsigned long num_asids; +unsigned long asid_mask; + +static atomic_long_t current_version; + +static DEFINE_RAW_SPINLOCK(context_lock); +static cpumask_t context_tlb_flush_pending; +static unsigned long *context_asid_map; + +static DEFINE_PER_CPU(atomic_long_t, active_context); +static DEFINE_PER_CPU(unsigned long, reserved_context); + +static bool check_update_reserved_context(unsigned long cntx, + unsigned long newcntx) +{ + int cpu; + bool hit = false; + + /* + * Iterate over the set of reserved CONTEXT looking for a match. + * If we find one, then we can update our mm to use new CONTEXT + * (i.e. the same CONTEXT in the current_version) but we can't + * exit the loop early, since we need to ensure that all copies + * of the old CONTEXT are updated to reflect the mm. Failure to do + * so could result in us missing the reserved CONTEXT in a future + * version. + */ + for_each_possible_cpu(cpu) { + if (per_cpu(reserved_context, cpu) == cntx) { + hit = true; + per_cpu(reserved_context, cpu) = newcntx; + } + } + + return hit; +} + +static void __flush_context(void) +{ + int i; + unsigned long cntx; + + /* Must be called with context_lock held */ + lockdep_assert_held(&context_lock); + + /* Update the list of reserved ASIDs and the ASID bitmap. */ + bitmap_zero(context_asid_map, num_asids); + + /* Mark already active ASIDs as used */ + for_each_possible_cpu(i) { + cntx = atomic_long_xchg_relaxed(&per_cpu(active_context, i), 0); + /* + * If this CPU has already been through a rollover, but + * hasn't run another task in the meantime, we must preserve + * its reserved CONTEXT, as this is the only trace we have of + * the process it is still running. + */ + if (cntx == 0) + cntx = per_cpu(reserved_context, i); + + __set_bit(cntx & asid_mask, context_asid_map); + per_cpu(reserved_context, i) = cntx; + } + + /* Mark ASID #0 as used because it is used at boot-time */ + __set_bit(0, context_asid_map); + + /* Queue a TLB invalidation for each CPU on next context-switch */ + cpumask_setall(&context_tlb_flush_pending); +} + +static unsigned long __new_context(struct mm_struct *mm) +{ + static u32 cur_idx = 1; + unsigned long cntx = atomic_long_read(&mm->context.id); + unsigned long asid, ver = atomic_long_read(¤t_version); + + /* Must be called with context_lock held */ + lockdep_assert_held(&context_lock); + + if (cntx != 0) { + unsigned long newcntx = ver | (cntx & asid_mask); + + /* + * If our current CONTEXT was active during a rollover, we + * can continue to use it and this was just a false alarm. + */ + if (check_update_reserved_context(cntx, newcntx)) + return newcntx; + + /* + * We had a valid CONTEXT in a previous life, so try to + * re-use it if possible. + */ + if (!__test_and_set_bit(cntx & asid_mask, context_asid_map)) + return newcntx; + } + + /* + * Allocate a free ASID. If we can't find one then increment + * current_version and flush all ASIDs. + */ + asid = find_next_zero_bit(context_asid_map, num_asids, cur_idx); + if (asid != num_asids) + goto set_asid; + + /* We're out of ASIDs, so increment current_version */ + ver = atomic_long_add_return_relaxed(num_asids, ¤t_version); + + /* Flush everything */ + __flush_context(); + + /* We have more ASIDs than CPUs, so this will always succeed */ + asid = find_next_zero_bit(context_asid_map, num_asids, 1); + +set_asid: + __set_bit(asid, context_asid_map); + cur_idx = asid; + return asid | ver; +} + +static void set_mm_asid(struct mm_struct *mm, unsigned int cpu) +{ + unsigned long flags; + bool need_flush_tlb = false; + unsigned long cntx, old_active_cntx; + + cntx = atomic_long_read(&mm->context.id); + + /* + * If our active_context is non-zero and the context matches the + * current_version, then we update the active_context entry with a + * relaxed cmpxchg. + * + * Following is how we handle racing with a concurrent rollover: + * + * - We get a zero back from the cmpxchg and end up waiting on the + * lock. Taking the lock synchronises with the rollover and so + * we are forced to see the updated verion. + * + * - We get a valid context back from the cmpxchg then we continue + * using old ASID because __flush_context() would have marked ASID + * of active_context as used and next context switch we will + * allocate new context. + */ + old_active_cntx = atomic_long_read(&per_cpu(active_context, cpu)); + if (old_active_cntx && + ((cntx & ~asid_mask) == atomic_long_read(¤t_version)) && + atomic_long_cmpxchg_relaxed(&per_cpu(active_context, cpu), + old_active_cntx, cntx)) + goto switch_mm_fast; + + raw_spin_lock_irqsave(&context_lock, flags); + + /* Check that our ASID belongs to the current_version. */ + cntx = atomic_long_read(&mm->context.id); + if ((cntx & ~asid_mask) != atomic_long_read(¤t_version)) { + cntx = __new_context(mm); + atomic_long_set(&mm->context.id, cntx); + } + + if (cpumask_test_and_clear_cpu(cpu, &context_tlb_flush_pending)) + need_flush_tlb = true; + + atomic_long_set(&per_cpu(active_context, cpu), cntx); + + raw_spin_unlock_irqrestore(&context_lock, flags); + +switch_mm_fast: + csr_write(CSR_SATP, virt_to_pfn(mm->pgd) | + ((cntx & asid_mask) << SATP_ASID_SHIFT) | + satp_mode); + + if (need_flush_tlb) + local_flush_tlb_all(); +} + +static void set_mm_noasid(struct mm_struct *mm) +{ + /* Switch the page table and blindly nuke entire local TLB */ + csr_write(CSR_SATP, virt_to_pfn(mm->pgd) | satp_mode); + local_flush_tlb_all(); +} + +static inline void set_mm(struct mm_struct *prev, + struct mm_struct *next, unsigned int cpu) +{ + /* + * The mm_cpumask indicates which harts' TLBs contain the virtual + * address mapping of the mm. Compared to noasid, using asid + * can't guarantee that stale TLB entries are invalidated because + * the asid mechanism wouldn't flush TLB for every switch_mm for + * performance. So when using asid, keep all CPUs footmarks in + * cpumask() until mm reset. + */ + cpumask_set_cpu(cpu, mm_cpumask(next)); + if (static_branch_unlikely(&use_asid_allocator)) { + set_mm_asid(next, cpu); + } else { + cpumask_clear_cpu(cpu, mm_cpumask(prev)); + set_mm_noasid(next); + } +} + +static int __init asids_init(void) +{ + unsigned long old; + + /* Figure-out number of ASID bits in HW */ + old = csr_read(CSR_SATP); + asid_bits = old | (SATP_ASID_MASK << SATP_ASID_SHIFT); + csr_write(CSR_SATP, asid_bits); + asid_bits = (csr_read(CSR_SATP) >> SATP_ASID_SHIFT) & SATP_ASID_MASK; + asid_bits = fls_long(asid_bits); + csr_write(CSR_SATP, old); + + /* + * In the process of determining number of ASID bits (above) + * we polluted the TLB of current HART so let's do TLB flushed + * to remove unwanted TLB enteries. + */ + local_flush_tlb_all(); + + /* Pre-compute ASID details */ + if (asid_bits) { + num_asids = 1 << asid_bits; + asid_mask = num_asids - 1; + } + + /* + * Use ASID allocator only if number of HW ASIDs are + * at-least twice more than CPUs + */ + if (num_asids > (2 * num_possible_cpus())) { + atomic_long_set(¤t_version, num_asids); + + context_asid_map = bitmap_zalloc(num_asids, GFP_KERNEL); + if (!context_asid_map) + panic("Failed to allocate bitmap for %lu ASIDs\n", + num_asids); + + __set_bit(0, context_asid_map); + + static_branch_enable(&use_asid_allocator); + + pr_info("ASID allocator using %lu bits (%lu entries)\n", + asid_bits, num_asids); + } else { + pr_info("ASID allocator disabled (%lu bits)\n", asid_bits); + } + + return 0; +} +early_initcall(asids_init); +#else +static inline void set_mm(struct mm_struct *prev, + struct mm_struct *next, unsigned int cpu) +{ + /* Nothing to do here when there is no MMU */ +} +#endif + /* * When necessary, performs a deferred icache flush for the given MM context, * on the local CPU. RISC-V has no direct mechanism for instruction cache @@ -20,11 +294,12 @@ * cache flush to be performed before execution resumes on each hart. This * actually performs that local instruction cache flush, which implicitly only * refers to the current hart. + * + * The "cpu" argument must be the current local CPU number. */ -static inline void flush_icache_deferred(struct mm_struct *mm) +static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu) { #ifdef CONFIG_SMP - unsigned int cpu = smp_processor_id(); cpumask_t *mask = &mm->context.icache_stale_mask; if (cpumask_test_cpu(cpu, mask)) { @@ -48,6 +323,8 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, if (unlikely(prev == next)) return; + membarrier_arch_switch_mm(prev, next, task); + /* * Mark the current MM context as inactive, and the next as * active. This is at least used by the icache flushing @@ -55,13 +332,7 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, */ cpu = smp_processor_id(); - cpumask_clear_cpu(cpu, mm_cpumask(prev)); - cpumask_set_cpu(cpu, mm_cpumask(next)); - -#ifdef CONFIG_MMU - csr_write(CSR_SATP, virt_to_pfn(next->pgd) | SATP_MODE); - local_flush_tlb_all(); -#endif + set_mm(prev, next, cpu); - flush_icache_deferred(next); + flush_icache_deferred(next, cpu); } |