GNU Linux-libre 4.4.284-gnu1

[releases.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/module.h>
#include <linux/cpu.h>
#include <linux/debugfs.h>

#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/nospec-branch.h>
#include <asm/cache.h>
#include <asm/apic.h>
#include <asm/uv/uv.h>
#include <asm/kaiser.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
 */

/*
 * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer which is
 * stored in cpu_tlb_state.last_user_mm_ibpb.
 */
#define LAST_USER_MM_IBPB       0x1UL

atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);

struct flush_tlb_info {
        struct mm_struct *flush_mm;
        unsigned long flush_start;
        unsigned long flush_end;
};

static void load_new_mm_cr3(pgd_t *pgdir)
{
        unsigned long new_mm_cr3 = __pa(pgdir);

        if (kaiser_enabled) {
                /*
                 * We reuse the same PCID for different tasks, so we must
                 * flush all the entries for the PCID out when we change tasks.
                 * Flush KERN below, flush USER when returning to userspace in
                 * kaiser's SWITCH_USER_CR3 (_SWITCH_TO_USER_CR3) macro.
                 *
                 * invpcid_flush_single_context(X86_CR3_PCID_ASID_USER) could
                 * do it here, but can only be used if X86_FEATURE_INVPCID is
                 * available - and many machines support pcid without invpcid.
                 *
                 * If X86_CR3_PCID_KERN_FLUSH actually added something, then it
                 * would be needed in the write_cr3() below - if PCIDs enabled.
                 */
                BUILD_BUG_ON(X86_CR3_PCID_KERN_FLUSH);
                kaiser_flush_tlb_on_return_to_user();
        }

        /*
         * Caution: many callers of this function expect
         * that load_cr3() is serializing and orders TLB
         * fills with respect to the mm_cpumask writes.
         */
        write_cr3(new_mm_cr3);
}

/*
 * We cannot call mmdrop() because we are in interrupt context,
 * instead update mm->cpu_vm_mask.
 */
void leave_mm(int cpu)
{
        struct mm_struct *active_mm = this_cpu_read(cpu_tlbstate.active_mm);
        if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK)
                BUG();
        if (cpumask_test_cpu(cpu, mm_cpumask(active_mm))) {
                cpumask_clear_cpu(cpu, mm_cpumask(active_mm));
                load_new_mm_cr3(swapper_pg_dir);
                /*
                 * This gets called in the idle path where RCU
                 * functions differently.  Tracing normally
                 * uses RCU, so we have to call the tracepoint
                 * specially here.
                 */
                trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
        }
}
EXPORT_SYMBOL_GPL(leave_mm);

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);
}

static inline unsigned long mm_mangle_tif_spec_ib(struct task_struct *next)
{
        unsigned long next_tif = task_thread_info(next)->flags;
        unsigned long ibpb = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_IBPB;

        return (unsigned long)next->mm | ibpb;
}

static void cond_ibpb(struct task_struct *next)
{
        if (!next || !next->mm)
                return;

        /*
         * Both, the conditional and the always IBPB mode use the mm
         * pointer to avoid the IBPB when switching between tasks of the
         * same process. Using the mm pointer instead of mm->context.ctx_id
         * opens a hypothetical hole vs. mm_struct reuse, which is more or
         * less impossible to control by an attacker. Aside of that it
         * would only affect the first schedule so the theoretically
         * exposed data is not really interesting.
         */
        if (static_branch_likely(&switch_mm_cond_ibpb)) {
                unsigned long prev_mm, next_mm;

                /*
                 * This is a bit more complex than the always mode because
                 * it has to handle two cases:
                 *
                 * 1) Switch from a user space task (potential attacker)
                 *    which has TIF_SPEC_IB set to a user space task
                 *    (potential victim) which has TIF_SPEC_IB not set.
                 *
                 * 2) Switch from a user space task (potential attacker)
                 *    which has TIF_SPEC_IB not set to a user space task
                 *    (potential victim) which has TIF_SPEC_IB set.
                 *
                 * This could be done by unconditionally issuing IBPB when
                 * a task which has TIF_SPEC_IB set is either scheduled in
                 * or out. Though that results in two flushes when:
                 *
                 * - the same user space task is scheduled out and later
                 *   scheduled in again and only a kernel thread ran in
                 *   between.
                 *
                 * - a user space task belonging to the same process is
                 *   scheduled in after a kernel thread ran in between
                 *
                 * - a user space task belonging to the same process is
                 *   scheduled in immediately.
                 *
                 * Optimize this with reasonably small overhead for the
                 * above cases. Mangle the TIF_SPEC_IB bit into the mm
                 * pointer of the incoming task which is stored in
                 * cpu_tlbstate.last_user_mm_ibpb for comparison.
                 */
                next_mm = mm_mangle_tif_spec_ib(next);
                prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_ibpb);

                /*
                 * Issue IBPB only if the mm's are different and one or
                 * both have the IBPB bit set.
                 */
                if (next_mm != prev_mm &&
                    (next_mm | prev_mm) & LAST_USER_MM_IBPB)
                        indirect_branch_prediction_barrier();

                this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, next_mm);
        }

        if (static_branch_unlikely(&switch_mm_always_ibpb)) {
                /*
                 * Only flush when switching to a user space task with a
                 * different context than the user space task which ran
                 * last on this CPU.
                 */
                if (this_cpu_read(cpu_tlbstate.last_user_mm) != next->mm) {
                        indirect_branch_prediction_barrier();
                        this_cpu_write(cpu_tlbstate.last_user_mm, next->mm);
                }
        }
}

void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
                        struct task_struct *tsk)
{
        unsigned cpu = smp_processor_id();

        if (likely(prev != next)) {
                /*
                 * Avoid user/user BTB poisoning by flushing the branch
                 * predictor when switching between processes. This stops
                 * one process from doing Spectre-v2 attacks on another.
                 */
                cond_ibpb(tsk);

                this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK);
                this_cpu_write(cpu_tlbstate.active_mm, next);
                cpumask_set_cpu(cpu, mm_cpumask(next));

                /*
                 * Re-load page tables.
                 *
                 * This logic has an ordering constraint:
                 *
                 *  CPU 0: Write to a PTE for 'next'
                 *  CPU 0: load bit 1 in mm_cpumask.  if nonzero, send IPI.
                 *  CPU 1: set bit 1 in next's mm_cpumask
                 *  CPU 1: load from the PTE that CPU 0 writes (implicit)
                 *
                 * We need to prevent an outcome in which CPU 1 observes
                 * the new PTE value and CPU 0 observes bit 1 clear in
                 * mm_cpumask.  (If that occurs, then the IPI will never
                 * be sent, and CPU 0's TLB will contain a stale entry.)
                 *
                 * The bad outcome can occur if either CPU's load is
                 * reordered before that CPU's store, so both CPUs must
                 * execute full barriers to prevent this from happening.
                 *
                 * Thus, switch_mm needs a full barrier between the
                 * store to mm_cpumask and any operation that could load
                 * from next->pgd.  TLB fills are special and can happen
                 * due to instruction fetches or for no reason at all,
                 * and neither LOCK nor MFENCE orders them.
                 * Fortunately, load_cr3() is serializing and gives the
                 * ordering guarantee we need.
                 *
                 */
                load_new_mm_cr3(next->pgd);

                trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);

                /* Stop flush ipis for the previous mm */
                cpumask_clear_cpu(cpu, mm_cpumask(prev));

                /* Load per-mm CR4 state */
                load_mm_cr4(next);

#ifdef CONFIG_MODIFY_LDT_SYSCALL
                /*
                 * Load the LDT, if the LDT is different.
                 *
                 * It's possible that prev->context.ldt doesn't match
                 * the LDT register.  This can happen if leave_mm(prev)
                 * was called and then modify_ldt changed
                 * prev->context.ldt but suppressed an IPI to this CPU.
                 * In this case, prev->context.ldt != NULL, because we
                 * never set context.ldt to NULL while the mm still
                 * exists.  That means that next->context.ldt !=
                 * prev->context.ldt, because mms never share an LDT.
                 */
                if (unlikely(prev->context.ldt != next->context.ldt))
                        load_mm_ldt(next);
#endif
        } else {
                this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK);
                BUG_ON(this_cpu_read(cpu_tlbstate.active_mm) != next);

                if (!cpumask_test_cpu(cpu, mm_cpumask(next))) {
                        /*
                         * On established mms, the mm_cpumask is only changed
                         * from irq context, from ptep_clear_flush() while in
                         * lazy tlb mode, and here. Irqs are blocked during
                         * schedule, protecting us from simultaneous changes.
                         */
                        cpumask_set_cpu(cpu, mm_cpumask(next));

                        /*
                         * We were in lazy tlb mode and leave_mm disabled
                         * tlb flush IPI delivery. We must reload CR3
                         * to make sure to use no freed page tables.
                         *
                         * As above, load_cr3() is serializing and orders TLB
                         * fills with respect to the mm_cpumask write.
                         */
                        load_new_mm_cr3(next->pgd);
                        trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
                        load_mm_cr4(next);
                        load_mm_ldt(next);
                }
        }
}

/*
 * The flush IPI assumes that a thread switch happens in this order:
 * [cpu0: the cpu that switches]
 * 1) switch_mm() either 1a) or 1b)
 * 1a) thread switch to a different mm
 * 1a1) set cpu_tlbstate to TLBSTATE_OK
 *      Now the tlb flush NMI handler flush_tlb_func won't call leave_mm
 *      if cpu0 was in lazy tlb mode.
 * 1a2) update cpu active_mm
 *      Now cpu0 accepts tlb flushes for the new mm.
 * 1a3) cpu_set(cpu, new_mm->cpu_vm_mask);
 *      Now the other cpus will send tlb flush ipis.
 * 1a4) change cr3.
 * 1a5) cpu_clear(cpu, old_mm->cpu_vm_mask);
 *      Stop ipi delivery for the old mm. This is not synchronized with
 *      the other cpus, but flush_tlb_func ignore flush ipis for the wrong
 *      mm, and in the worst case we perform a superfluous tlb flush.
 * 1b) thread switch without mm change
 *      cpu active_mm is correct, cpu0 already handles flush ipis.
 * 1b1) set cpu_tlbstate to TLBSTATE_OK
 * 1b2) test_and_set the cpu bit in cpu_vm_mask.
 *      Atomically set the bit [other cpus will start sending flush ipis],
 *      and test the bit.
 * 1b3) if the bit was 0: leave_mm was called, flush the tlb.
 * 2) switch %%esp, ie current
 *
 * The interrupt must handle 2 special cases:
 * - cr3 is changed before %%esp, ie. it cannot use current->{active_,}mm.
 * - the cpu performs speculative tlb reads, i.e. even if the cpu only
 *   runs in kernel space, the cpu could load tlb entries for user space
 *   pages.
 *
 * The good news is that cpu_tlbstate is local to each cpu, no
 * write/read ordering problems.
 */

/*
 * TLB flush funcation:
 * 1) Flush the tlb entries if the cpu uses the mm that's being flushed.
 * 2) Leave the mm if we are in the lazy tlb mode.
 */
static void flush_tlb_func(void *info)
{
        struct flush_tlb_info *f = info;

        inc_irq_stat(irq_tlb_count);

        if (f->flush_mm && f->flush_mm != this_cpu_read(cpu_tlbstate.active_mm))
                return;

        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
        if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
                if (f->flush_end == TLB_FLUSH_ALL) {
                        local_flush_tlb();
                        trace_tlb_flush(TLB_REMOTE_SHOOTDOWN, TLB_FLUSH_ALL);
                } else {
                        unsigned long addr;
                        unsigned long nr_pages =
                                (f->flush_end - f->flush_start) / PAGE_SIZE;
                        addr = f->flush_start;
                        while (addr < f->flush_end) {
                                __flush_tlb_single(addr);
                                addr += PAGE_SIZE;
                        }
                        trace_tlb_flush(TLB_REMOTE_SHOOTDOWN, nr_pages);
                }
        } else
                leave_mm(smp_processor_id());

}

void native_flush_tlb_others(const struct cpumask *cpumask,
                                 struct mm_struct *mm, unsigned long start,
                                 unsigned long end)
{
        struct flush_tlb_info info;

        info.flush_mm = mm;
        info.flush_start = start;
        info.flush_end = end;

        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
        if (end == TLB_FLUSH_ALL)
                trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
        else
                trace_tlb_flush(TLB_REMOTE_SEND_IPI,
                                (end - start) >> PAGE_SHIFT);

        if (is_uv_system()) {
                unsigned int cpu;

                cpu = smp_processor_id();
                cpumask = uv_flush_tlb_others(cpumask, mm, start, end, cpu);
                if (cpumask)
                        smp_call_function_many(cpumask, flush_tlb_func,
                                                                &info, 1);
                return;
        }
        smp_call_function_many(cpumask, flush_tlb_func, &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)
{
        unsigned long addr;
        /* do a global flush by default */
        unsigned long base_pages_to_flush = TLB_FLUSH_ALL;

        preempt_disable();

        if ((end != TLB_FLUSH_ALL) && !(vmflag & VM_HUGETLB))
                base_pages_to_flush = (end - start) >> PAGE_SHIFT;
        if (base_pages_to_flush > tlb_single_page_flush_ceiling)
                base_pages_to_flush = TLB_FLUSH_ALL;

        if (current->active_mm != mm) {
                /* Synchronize with switch_mm. */
                smp_mb();

                goto out;
        }

        if (!current->mm) {
                leave_mm(smp_processor_id());

                /* Synchronize with switch_mm. */
                smp_mb();

                goto out;
        }

        /*
         * Both branches below are implicit full barriers (MOV to CR or
         * INVLPG) that synchronize with switch_mm.
         */
        if (base_pages_to_flush == TLB_FLUSH_ALL) {
                count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
                local_flush_tlb();
        } else {
                /* flush range by one by one 'invlpg' */
                for (addr = start; addr < end;  addr += PAGE_SIZE) {
                        count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);
                        __flush_tlb_single(addr);
                }
        }
        trace_tlb_flush(TLB_LOCAL_MM_SHOOTDOWN, base_pages_to_flush);
out:
        if (base_pages_to_flush == TLB_FLUSH_ALL) {
                start = 0UL;
                end = TLB_FLUSH_ALL;
        }
        if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
                flush_tlb_others(mm_cpumask(mm), mm, start, end);
        preempt_enable();
}

static void do_flush_tlb_all(void *info)
{
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
        __flush_tlb_all();
        if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_LAZY)
                leave_mm(smp_processor_id());
}

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->flush_start; addr < f->flush_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_SIZE) {
                on_each_cpu(do_flush_tlb_all, NULL, 1);
        } else {
                struct flush_tlb_info info;
                info.flush_start = start;
                info.flush_end = end;
                on_each_cpu(do_kernel_range_flush, &info, 1);
        }
}

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);