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x86/mm/tlb: Open-code on_each_cpu_cond_mask() for tlb_is_not_lazy()

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Open-code on_each_cpu_cond_mask() in native_flush_tlb_others() to
optimize the code. Open-coding eliminates the need for the indirect branch
that is used to call is_lazy(), and in CPUs that are vulnerable to
Spectre v2, it eliminates the retpoline. In addition, it allows to use a
preallocated cpumask to compute the CPUs that should be.

This would later allow us not to adapt on_each_cpu_cond_mask() to
support local and remote functions.

Note that calling tlb_is_not_lazy() for every CPU that needs to be
flushed, as done in native_flush_tlb_multi() might look ugly, but it is
equivalent to what is currently done in on_each_cpu_cond_mask().
Actually, native_flush_tlb_multi() does it more efficiently since it
avoids using an indirect branch for the matter.

Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20210220231712.2475218-4-namit@vmware.com
This commit is contained in:
Nadav Amit 2021-02-20 15:17:06 -08:00 committed by Ingo Molnar
parent 4c1ba3923e
commit 6035152d8e
1 changed files with 32 additions and 5 deletions
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37
arch/x86/mm/tlb.c
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@ -788,11 +788,13 @@ done:
nr_invalidate); nr_invalidate);
} }
static bool tlb_is_not_lazy(int cpu, void *data) static bool tlb_is_not_lazy(int cpu)
{ {
return !per_cpu(cpu_tlbstate.is_lazy, cpu); return !per_cpu(cpu_tlbstate.is_lazy, cpu);
} }
static DEFINE_PER_CPU(cpumask_t, flush_tlb_mask);
STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask, STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask,
const struct flush_tlb_info *info) const struct flush_tlb_info *info)
{ {
@ -813,12 +815,37 @@ STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask,
* up on the new contents of what used to be page tables, while * up on the new contents of what used to be page tables, while
* doing a speculative memory access. * doing a speculative memory access.
*/ */
if (info->freed_tables) if (info->freed_tables) {
smp_call_function_many(cpumask, flush_tlb_func, smp_call_function_many(cpumask, flush_tlb_func,
(void *)info, 1); (void *)info, 1);
else } else {
on_each_cpu_cond_mask(tlb_is_not_lazy, flush_tlb_func, /*
(void *)info, 1, cpumask); * Although we could have used on_each_cpu_cond_mask(),
* open-coding it has performance advantages, as it eliminates
* the need for indirect calls or retpolines. In addition, it
* allows to use a designated cpumask for evaluating the
* condition, instead of allocating one.
*
* This code works under the assumption that there are no nested
* TLB flushes, an assumption that is already made in
* flush_tlb_mm_range().
*
* cond_cpumask is logically a stack-local variable, but it is
* more efficient to have it off the stack and not to allocate
* it on demand. Preemption is disabled and this code is
* non-reentrant.
*/
struct cpumask *cond_cpumask = this_cpu_ptr(&flush_tlb_mask);
int cpu;
cpumask_clear(cond_cpumask);
for_each_cpu(cpu, cpumask) {
if (tlb_is_not_lazy(cpu))
__cpumask_set_cpu(cpu, cond_cpumask);
}
smp_call_function_many(cond_cpumask, flush_tlb_func, (void *)info, 1);
}
} }
void flush_tlb_others(const struct cpumask *cpumask, void flush_tlb_others(const struct cpumask *cpumask,