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SubjectRe: [PATCH 3/9] x86/mm/tlb: Refactor common code into flush_tlb_on_cpus()
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On 6/12/19 11:48 PM, Nadav Amit wrote:
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 91f6db92554c..c34bcf03f06f 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -734,7 +734,11 @@ static inline struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm,
> unsigned int stride_shift, bool freed_tables,
> u64 new_tlb_gen)
> {
> - struct flush_tlb_info *info = this_cpu_ptr(&flush_tlb_info);
> + struct flush_tlb_info *info;
> +
> + preempt_disable();
> +
> + info = this_cpu_ptr(&flush_tlb_info);
>
> #ifdef CONFIG_DEBUG_VM
> /*
> @@ -762,6 +766,23 @@ static inline void put_flush_tlb_info(void)
> barrier();
> this_cpu_dec(flush_tlb_info_idx);
> #endif
> + preempt_enable();
> +}

The addition of this disable/enable pair is unchangelogged and
uncommented. I think it makes sense since we do need to make sure we
stay on this CPU, but it would be nice to mention.

> +static void flush_tlb_on_cpus(const cpumask_t *cpumask,
> + const struct flush_tlb_info *info)
> +{

Might be nice to mention that preempt must be disabled. It's kinda
implied from the smp_processor_id(), but being explicit is always nice too.

> + int this_cpu = smp_processor_id();
> +
> + if (cpumask_test_cpu(this_cpu, cpumask)) {
> + lockdep_assert_irqs_enabled();
> + local_irq_disable();
> + flush_tlb_func_local(info, TLB_LOCAL_MM_SHOOTDOWN);
> + local_irq_enable();
> + }
> +
> + if (cpumask_any_but(cpumask, this_cpu) < nr_cpu_ids)
> + flush_tlb_others(cpumask, info);
> }
>
> void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
> @@ -770,9 +791,6 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
> {
> struct flush_tlb_info *info;
> u64 new_tlb_gen;
> - int cpu;
> -
> - cpu = get_cpu();
>
> /* Should we flush just the requested range? */
> if ((end == TLB_FLUSH_ALL) ||
> @@ -787,18 +805,18 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
> info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables,
> new_tlb_gen);
>
> - if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
> - lockdep_assert_irqs_enabled();
> - local_irq_disable();
> - flush_tlb_func_local(info, TLB_LOCAL_MM_SHOOTDOWN);
> - local_irq_enable();
> - }
> + /*
> + * Assert that mm_cpumask() corresponds with the loaded mm. We got one
> + * exception: for init_mm we do not need to flush anything, and the
> + * cpumask does not correspond with loaded_mm.
> + */
> + VM_WARN_ON_ONCE(cpumask_test_cpu(smp_processor_id(), mm_cpumask(mm)) !=
> + (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) &&
> + mm != &init_mm);

Very very cool. You thought "these should be equivalent", and you added
a corresponding warning to ensure they are.

> - if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids)
> - flush_tlb_others(mm_cpumask(mm), info);
> + flush_tlb_on_cpus(mm_cpumask(mm), info);
>
> put_flush_tlb_info();
> - put_cpu();
> }



Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>

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