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);
bool was_lazy = this_cpu_read(cpu_tlbstate.is_lazy);
unsigned cpu = smp_processor_id();
u64 next_tlb_gen;
bool need_flush;
u16 new_asid;
/*
* 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()).
*
* Only do this check if CONFIG_DEBUG_VM=y because __read_cr3()
* isn't free.
*/
#ifdef CONFIG_DEBUG_VM
if (WARN_ON_ONCE(__read_cr3() != build_cr3(real_prev->pgd, prev_asid))) {
/*
* If we were to BUG here, we'd be very likely to kill
* the system so hard that we don't see the call trace.
* Try to recover instead by ignoring the error and doing
* a global flush to minimize the chance of corruption.
*
* (This is far from being a fully correct recovery.
* Architecturally, the CPU could prefetch something
* back into an incorrect ASID slot and leave it there
* to cause trouble down the road. It's better than
* nothing, though.)
*/
__flush_tlb_all();
}
#endif
this_cpu_write(cpu_tlbstate.is_lazy, false);
/*
* The membarrier system call requires a full memory barrier and
* core serialization before returning to user-space, after
* storing to rq->curr. Writing to CR3 provides that full
* memory barrier and core serializing instruction.
*/
if (real_prev == next) {
VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
next->context.ctx_id);
/*
* Even in lazy TLB mode, the CPU should stay set in the
* mm_cpumask. The TLB shootdown code can figure out from
* from cpu_tlbstate.is_lazy whether or not to send an IPI.
*/
if (WARN_ON_ONCE(real_prev != &init_mm &&
!cpumask_test_cpu(cpu, mm_cpumask(next))))
cpumask_set_cpu(cpu, mm_cpumask(next));
/*
* If the CPU is not in lazy TLB mode, we are just switching
* from one thread in a process to another thread in the same
* process. No TLB flush required.
*/
if (!was_lazy)
return;
/*
* Read the tlb_gen to check whether a flush is needed.
* If the TLB is up to date, just use it.
* The barrier synchronizes with the tlb_gen increment in
* the TLB shootdown code.
*/
smp_mb();
next_tlb_gen = atomic64_read(&next->context.tlb_gen);
if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) ==
next_tlb_gen)
return;
/*
* TLB contents went out of date while we were in lazy
* mode. Fall through to the TLB switching code below.
*/
new_asid = prev_asid;
need_flush = true;
} else {
/*
* 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);
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.
*/
sync_current_stack_to_mm(next);
}
/*
* Stop remote flushes for the previous mm.
* Skip kernel threads; we never send init_mm TLB flushing IPIs,
* but the bitmap manipulation can cause cache line contention.
*/
if (real_prev != &init_mm) {
VM_WARN_ON_ONCE(!cpumask_test_cpu(cpu,
mm_cpumask(real_prev)));
cpumask_clear_cpu(cpu, mm_cpumask(real_prev));
}
/*
* Start remote flushes and then read tlb_gen.
*/
if (next != &init_mm)
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);
/* Let nmi_uaccess_okay() know that we're changing CR3. */
this_cpu_write(cpu_tlbstate.loaded_mm, LOADED_MM_SWITCHING);
barrier();
}
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);
load_new_mm_cr3(next->pgd, new_asid, true);
/*
* NB: This gets called via leave_mm() in the idle path
* where RCU functions differently. Tracing normally
* uses RCU, so we need to use the _rcuidle variant.
*
* (There is no good reason for this. The idle code should
* be rearranged to call this before rcu_idle_enter().)
*/
trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
} else {
/* The new ASID is already up to date. */
load_new_mm_cr3(next->pgd, new_asid, false);
/* See above wrt _rcuidle. */
trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, 0);
}
/* Make sure we write CR3 before loaded_mm. */
barrier();
this_cpu_write(cpu_tlbstate.loaded_mm, next);
this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid);
if (next != real_prev) {
load_mm_cr4(next);
switch_ldt(real_prev, next);
}
}
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()).
*
* Only do this check if CONFIG_DEBUG_VM=y because __read_cr3()
* isn't free.
*/
#ifdef CONFIG_DEBUG_VM
if (WARN_ON_ONCE(__read_cr3() != build_cr3(real_prev->pgd, prev_asid))) {
/*
* If we were to BUG here, we'd be very likely to kill
* the system so hard that we don't see the call trace.
* Try to recover instead by ignoring the error and doing
* a global flush to minimize the chance of corruption.
*
* (This is far from being a fully correct recovery.
* Architecturally, the CPU could prefetch something
* back into an incorrect ASID slot and leave it there
* to cause trouble down the road. It's better than
* nothing, though.)
*/
__flush_tlb_all();
}
#endif
this_cpu_write(cpu_tlbstate.is_lazy, false);
if (real_prev == next) {
VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
next->context.ctx_id);
/*
* We don't currently support having a real mm loaded without
* our cpu set in mm_cpumask(). We have all the bookkeeping
* in place to figure out whether we would need to flush
* if our cpu were cleared in mm_cpumask(), but we don't
* currently use it.
*/
if (WARN_ON_ONCE(real_prev != &init_mm &&
!cpumask_test_cpu(cpu, mm_cpumask(next))))
cpumask_set_cpu(cpu, mm_cpumask(next));
return;
} 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.
*/
sync_current_stack_to_mm(next);
}
/* Stop remote flushes for the previous mm */
VM_WARN_ON_ONCE(!cpumask_test_cpu(cpu, mm_cpumask(real_prev)) &&
real_prev != &init_mm);
cpumask_clear_cpu(cpu, mm_cpumask(real_prev));
/*
* 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);
load_new_mm_cr3(next->pgd, new_asid, true);
/*
* NB: This gets called via leave_mm() in the idle path
* where RCU functions differently. Tracing normally
* uses RCU, so we need to use the _rcuidle variant.
*
* (There is no good reason for this. The idle code should
* be rearranged to call this before rcu_idle_enter().)
*/
trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
} else {
/* The new ASID is already up to date. */
load_new_mm_cr3(next->pgd, new_asid, false);
/* See above wrt _rcuidle. */
trace_tlb_flush_rcuidle(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);
}
