x86/mm: Implement PCID based optimization: try to preserve old TLB entries using PCID

[linux.git] / arch / x86 / mm / tlb.c

#include <linux/init.h>

#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/export.h>
#include <linux/cpu.h>

#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/cache.h>
#include <asm/apic.h>
#include <asm/uv/uv.h>
#include <linux/debugfs.h>

/*
 *      TLB flushing, formerly SMP-only
 *              c/o Linus Torvalds.
 *
 *      These mean you can really definitely utterly forget about
 *      writing to user space from interrupts. (Its not allowed anyway).
 *
 *      Optimizations Manfred Spraul <manfred@colorfullife.com>
 *
 *      More scalable flush, from Andi Kleen
 *
 *      Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi
 */

atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);

static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
                            u16 *new_asid, bool *need_flush)
{
        u16 asid;

        if (!static_cpu_has(X86_FEATURE_PCID)) {
                *new_asid = 0;
                *need_flush = true;
                return;
        }

        for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
                if (this_cpu_read(cpu_tlbstate.ctxs[asid].ctx_id) !=
                    next->context.ctx_id)
                        continue;

                *new_asid = asid;
                *need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) <
                               next_tlb_gen);
                return;
        }

        /*
         * We don't currently own an ASID slot on this CPU.
         * Allocate a slot.
         */
        *new_asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1;
        if (*new_asid >= TLB_NR_DYN_ASIDS) {
                *new_asid = 0;
                this_cpu_write(cpu_tlbstate.next_asid, 1);
        }
        *need_flush = true;
}

void leave_mm(int cpu)
{
        struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);

        /*
         * It's plausible that we're in lazy TLB mode while our mm is init_mm.
         * If so, our callers still expect us to flush the TLB, but there
         * aren't any user TLB entries in init_mm to worry about.
         *
         * This needs to happen before any other sanity checks due to
         * intel_idle's shenanigans.
         */
        if (loaded_mm == &init_mm)
                return;

        /* Warn if we're not lazy. */
        WARN_ON(cpumask_test_cpu(smp_processor_id(), mm_cpumask(loaded_mm)));

        switch_mm(NULL, &init_mm, NULL);
}

void switch_mm(struct mm_struct *prev, struct mm_struct *next,
               struct task_struct *tsk)
{
        unsigned long flags;

        local_irq_save(flags);
        switch_mm_irqs_off(prev, next, tsk);
        local_irq_restore(flags);
}

void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
                        struct task_struct *tsk)
{
        struct mm_struct *real_prev = this_cpu_read(cpu_tlbstate.loaded_mm);
        u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
        unsigned cpu = smp_processor_id();
        u64 next_tlb_gen;

        /*
         * NB: The scheduler will call us with prev == next when switching
         * from lazy TLB mode to normal mode if active_mm isn't changing.
         * When this happens, we don't assume that CR3 (and hence
         * cpu_tlbstate.loaded_mm) matches next.
         *
         * NB: leave_mm() calls us with prev == NULL and tsk == NULL.
         */

        /* We don't want flush_tlb_func_* to run concurrently with us. */
        if (IS_ENABLED(CONFIG_PROVE_LOCKING))
                WARN_ON_ONCE(!irqs_disabled());

        /*
         * Verify that CR3 is what we think it is.  This will catch
         * hypothetical buggy code that directly switches to swapper_pg_dir
         * without going through leave_mm() / switch_mm_irqs_off() or that
         * does something like write_cr3(read_cr3_pa()).
         */
        VM_BUG_ON(__read_cr3() != (__sme_pa(real_prev->pgd) | prev_asid));

        if (real_prev == next) {
                VM_BUG_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
                          next->context.ctx_id);

                if (cpumask_test_cpu(cpu, mm_cpumask(next))) {
                        /*
                         * There's nothing to do: we weren't lazy, and we
                         * aren't changing our mm.  We don't need to flush
                         * anything, nor do we need to update CR3, CR4, or
                         * LDTR.
                         */
                        return;
                }

                /* Resume remote flushes and then read tlb_gen. */
                cpumask_set_cpu(cpu, mm_cpumask(next));
                next_tlb_gen = atomic64_read(&next->context.tlb_gen);

                if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) <
                    next_tlb_gen) {
                        /*
                         * Ideally, we'd have a flush_tlb() variant that
                         * takes the known CR3 value as input.  This would
                         * be faster on Xen PV and on hypothetical CPUs
                         * on which INVPCID is fast.
                         */
                        this_cpu_write(cpu_tlbstate.ctxs[prev_asid].tlb_gen,
                                       next_tlb_gen);
                        write_cr3(__sme_pa(next->pgd) | prev_asid);
                        trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH,
                                        TLB_FLUSH_ALL);
                }

                /*
                 * We just exited lazy mode, which means that CR4 and/or LDTR
                 * may be stale.  (Changes to the required CR4 and LDTR states
                 * are not reflected in tlb_gen.)
                 */
        } else {
                u16 new_asid;
                bool need_flush;

                if (IS_ENABLED(CONFIG_VMAP_STACK)) {
                        /*
                         * If our current stack is in vmalloc space and isn't
                         * mapped in the new pgd, we'll double-fault.  Forcibly
                         * map it.
                         */
                        unsigned int index = pgd_index(current_stack_pointer());
                        pgd_t *pgd = next->pgd + index;

                        if (unlikely(pgd_none(*pgd)))
                                set_pgd(pgd, init_mm.pgd[index]);
                }

                /* Stop remote flushes for the previous mm */
                if (cpumask_test_cpu(cpu, mm_cpumask(real_prev)))
                        cpumask_clear_cpu(cpu, mm_cpumask(real_prev));

                VM_WARN_ON_ONCE(cpumask_test_cpu(cpu, mm_cpumask(next)));

                /*
                 * Start remote flushes and then read tlb_gen.
                 */
                cpumask_set_cpu(cpu, mm_cpumask(next));
                next_tlb_gen = atomic64_read(&next->context.tlb_gen);

                choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush);

                if (need_flush) {
                        this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id);
                        this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen);
                        write_cr3(__sme_pa(next->pgd) | new_asid);
                        trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH,
                                        TLB_FLUSH_ALL);
                } else {
                        /* The new ASID is already up to date. */
                        write_cr3(__sme_pa(next->pgd) | new_asid | CR3_NOFLUSH);
                        trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, 0);
                }

                this_cpu_write(cpu_tlbstate.loaded_mm, next);
                this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid);
        }

        load_mm_cr4(next);
        switch_ldt(real_prev, next);
}

/*
 * flush_tlb_func_common()'s memory ordering requirement is that any
 * TLB fills that happen after we flush the TLB are ordered after we
 * read active_mm's tlb_gen.  We don't need any explicit barriers
 * because all x86 flush operations are serializing and the
 * atomic64_read operation won't be reordered by the compiler.
 */
static void flush_tlb_func_common(const struct flush_tlb_info *f,
                                  bool local, enum tlb_flush_reason reason)
{
        /*
         * We have three different tlb_gen values in here.  They are:
         *
         * - mm_tlb_gen:     the latest generation.
         * - local_tlb_gen:  the generation that this CPU has already caught
         *                   up to.
         * - f->new_tlb_gen: the generation that the requester of the flush
         *                   wants us to catch up to.
         */
        struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
        u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
        u64 mm_tlb_gen = atomic64_read(&loaded_mm->context.tlb_gen);
        u64 local_tlb_gen = this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen);

        /* This code cannot presently handle being reentered. */
        VM_WARN_ON(!irqs_disabled());

        VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].ctx_id) !=
                   loaded_mm->context.ctx_id);

        if (!cpumask_test_cpu(smp_processor_id(), mm_cpumask(loaded_mm))) {
                /*
                 * We're in lazy mode -- don't flush.  We can get here on
                 * remote flushes due to races and on local flushes if a
                 * kernel thread coincidentally flushes the mm it's lazily
                 * still using.
                 */
                return;
        }

        if (unlikely(local_tlb_gen == mm_tlb_gen)) {
                /*
                 * There's nothing to do: we're already up to date.  This can
                 * happen if two concurrent flushes happen -- the first flush to
                 * be handled can catch us all the way up, leaving no work for
                 * the second flush.
                 */
                trace_tlb_flush(reason, 0);
                return;
        }

        WARN_ON_ONCE(local_tlb_gen > mm_tlb_gen);
        WARN_ON_ONCE(f->new_tlb_gen > mm_tlb_gen);

        /*
         * If we get to this point, we know that our TLB is out of date.
         * This does not strictly imply that we need to flush (it's
         * possible that f->new_tlb_gen <= local_tlb_gen), but we're
         * going to need to flush in the very near future, so we might
         * as well get it over with.
         *
         * The only question is whether to do a full or partial flush.
         *
         * We do a partial flush if requested and two extra conditions
         * are met:
         *
         * 1. f->new_tlb_gen == local_tlb_gen + 1.  We have an invariant that
         *    we've always done all needed flushes to catch up to
         *    local_tlb_gen.  If, for example, local_tlb_gen == 2 and
         *    f->new_tlb_gen == 3, then we know that the flush needed to bring
         *    us up to date for tlb_gen 3 is the partial flush we're
         *    processing.
         *
         *    As an example of why this check is needed, suppose that there
         *    are two concurrent flushes.  The first is a full flush that
         *    changes context.tlb_gen from 1 to 2.  The second is a partial
         *    flush that changes context.tlb_gen from 2 to 3.  If they get
         *    processed on this CPU in reverse order, we'll see
         *     local_tlb_gen == 1, mm_tlb_gen == 3, and end != TLB_FLUSH_ALL.
         *    If we were to use __flush_tlb_single() and set local_tlb_gen to
         *    3, we'd be break the invariant: we'd update local_tlb_gen above
         *    1 without the full flush that's needed for tlb_gen 2.
         *
         * 2. f->new_tlb_gen == mm_tlb_gen.  This is purely an optimiation.
         *    Partial TLB flushes are not all that much cheaper than full TLB
         *    flushes, so it seems unlikely that it would be a performance win
         *    to do a partial flush if that won't bring our TLB fully up to
         *    date.  By doing a full flush instead, we can increase
         *    local_tlb_gen all the way to mm_tlb_gen and we can probably
         *    avoid another flush in the very near future.
         */
        if (f->end != TLB_FLUSH_ALL &&
            f->new_tlb_gen == local_tlb_gen + 1 &&
            f->new_tlb_gen == mm_tlb_gen) {
                /* Partial flush */
                unsigned long addr;
                unsigned long nr_pages = (f->end - f->start) >> PAGE_SHIFT;

                addr = f->start;
                while (addr < f->end) {
                        __flush_tlb_single(addr);
                        addr += PAGE_SIZE;
                }
                if (local)
                        count_vm_tlb_events(NR_TLB_LOCAL_FLUSH_ONE, nr_pages);
                trace_tlb_flush(reason, nr_pages);
        } else {
                /* Full flush. */
                local_flush_tlb();
                if (local)
                        count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
                trace_tlb_flush(reason, TLB_FLUSH_ALL);
        }

        /* Both paths above update our state to mm_tlb_gen. */
        this_cpu_write(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen, mm_tlb_gen);
}

static void flush_tlb_func_local(void *info, enum tlb_flush_reason reason)
{
        const struct flush_tlb_info *f = info;

        flush_tlb_func_common(f, true, reason);
}

static void flush_tlb_func_remote(void *info)
{
        const struct flush_tlb_info *f = info;

        inc_irq_stat(irq_tlb_count);

        if (f->mm && f->mm != this_cpu_read(cpu_tlbstate.loaded_mm))
                return;

        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
        flush_tlb_func_common(f, false, TLB_REMOTE_SHOOTDOWN);
}

void native_flush_tlb_others(const struct cpumask *cpumask,
                             const struct flush_tlb_info *info)
{
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
        if (info->end == TLB_FLUSH_ALL)
                trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
        else
                trace_tlb_flush(TLB_REMOTE_SEND_IPI,
                                (info->end - info->start) >> PAGE_SHIFT);

        if (is_uv_system()) {
                /*
                 * This whole special case is confused.  UV has a "Broadcast
                 * Assist Unit", which seems to be a fancy way to send IPIs.
                 * Back when x86 used an explicit TLB flush IPI, UV was
                 * optimized to use its own mechanism.  These days, x86 uses
                 * smp_call_function_many(), but UV still uses a manual IPI,
                 * and that IPI's action is out of date -- it does a manual
                 * flush instead of calling flush_tlb_func_remote().  This
                 * means that the percpu tlb_gen variables won't be updated
                 * and we'll do pointless flushes on future context switches.
                 *
                 * Rather than hooking native_flush_tlb_others() here, I think
                 * that UV should be updated so that smp_call_function_many(),
                 * etc, are optimal on UV.
                 */
                unsigned int cpu;

                cpu = smp_processor_id();
                cpumask = uv_flush_tlb_others(cpumask, info);
                if (cpumask)
                        smp_call_function_many(cpumask, flush_tlb_func_remote,
                                               (void *)info, 1);
                return;
        }
        smp_call_function_many(cpumask, flush_tlb_func_remote,
                               (void *)info, 1);
}

/*
 * See Documentation/x86/tlb.txt for details.  We choose 33
 * because it is large enough to cover the vast majority (at
 * least 95%) of allocations, and is small enough that we are
 * confident it will not cause too much overhead.  Each single
 * flush is about 100 ns, so this caps the maximum overhead at
 * _about_ 3,000 ns.
 *
 * This is in units of pages.
 */
static unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;

void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
                                unsigned long end, unsigned long vmflag)
{
        int cpu;

        struct flush_tlb_info info = {
                .mm = mm,
        };

        cpu = get_cpu();

        /* This is also a barrier that synchronizes with switch_mm(). */
        info.new_tlb_gen = inc_mm_tlb_gen(mm);

        /* Should we flush just the requested range? */
        if ((end != TLB_FLUSH_ALL) &&
            !(vmflag & VM_HUGETLB) &&
            ((end - start) >> PAGE_SHIFT) <= tlb_single_page_flush_ceiling) {
                info.start = start;
                info.end = end;
        } else {
                info.start = 0UL;
                info.end = TLB_FLUSH_ALL;
        }

        if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
                VM_WARN_ON(irqs_disabled());
                local_irq_disable();
                flush_tlb_func_local(&info, TLB_LOCAL_MM_SHOOTDOWN);
                local_irq_enable();
        }

        if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids)
                flush_tlb_others(mm_cpumask(mm), &info);

        put_cpu();
}


static void do_flush_tlb_all(void *info)
{
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
        __flush_tlb_all();
}

void flush_tlb_all(void)
{
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
        on_each_cpu(do_flush_tlb_all, NULL, 1);
}

static void do_kernel_range_flush(void *info)
{
        struct flush_tlb_info *f = info;
        unsigned long addr;

        /* flush range by one by one 'invlpg' */
        for (addr = f->start; addr < f->end; addr += PAGE_SIZE)
                __flush_tlb_single(addr);
}

void flush_tlb_kernel_range(unsigned long start, unsigned long end)
{

        /* Balance as user space task's flush, a bit conservative */
        if (end == TLB_FLUSH_ALL ||
            (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
                on_each_cpu(do_flush_tlb_all, NULL, 1);
        } else {
                struct flush_tlb_info info;
                info.start = start;
                info.end = end;
                on_each_cpu(do_kernel_range_flush, &info, 1);
        }
}

void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
{
        struct flush_tlb_info info = {
                .mm = NULL,
                .start = 0UL,
                .end = TLB_FLUSH_ALL,
        };

        int cpu = get_cpu();

        if (cpumask_test_cpu(cpu, &batch->cpumask)) {
                VM_WARN_ON(irqs_disabled());
                local_irq_disable();
                flush_tlb_func_local(&info, TLB_LOCAL_SHOOTDOWN);
                local_irq_enable();
        }

        if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids)
                flush_tlb_others(&batch->cpumask, &info);

        cpumask_clear(&batch->cpumask);

        put_cpu();
}

static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
                             size_t count, loff_t *ppos)
{
        char buf[32];
        unsigned int len;

        len = sprintf(buf, "%ld\n", tlb_single_page_flush_ceiling);
        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}

static ssize_t tlbflush_write_file(struct file *file,
                 const char __user *user_buf, size_t count, loff_t *ppos)
{
        char buf[32];
        ssize_t len;
        int ceiling;

        len = min(count, sizeof(buf) - 1);
        if (copy_from_user(buf, user_buf, len))
                return -EFAULT;

        buf[len] = '\0';
        if (kstrtoint(buf, 0, &ceiling))
                return -EINVAL;

        if (ceiling < 0)
                return -EINVAL;

        tlb_single_page_flush_ceiling = ceiling;
        return count;
}

static const struct file_operations fops_tlbflush = {
        .read = tlbflush_read_file,
        .write = tlbflush_write_file,
        .llseek = default_llseek,
};

static int __init create_tlb_single_page_flush_ceiling(void)
{
        debugfs_create_file("tlb_single_page_flush_ceiling", S_IRUSR | S_IWUSR,
                            arch_debugfs_dir, NULL, &fops_tlbflush);
        return 0;
}
late_initcall(create_tlb_single_page_flush_ceiling);