lkml.org 
[lkml]   [2019]   [Jun]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH 3/9] x86/mm/tlb: Refactor common code into flush_tlb_on_cpus()
Date
> On Jun 25, 2019, at 2:07 PM, Dave Hansen <dave.hansen@intel.com> wrote:
>
> 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.

I’ll add some comments and update the changeling . I see I marked
get_flush_tlb_info() as “inline” for no reason. I’m going to remove it in
this patch, unless you say it should be in a separate patch.

>> +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.

I will add a comment, although smp_processor_id() should anyhow shout at you
if you use it with CONFIG_DEBUG_PREEMPT=y.

>> + 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.

The credit for this assertion goes to Peter who suggested I add it...

>
>> - 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>

Thanks for the reviews of this patch and the others (don’t worry, I won’t
add the “Reviewed-by” tag to the others).
\
 
 \ /
  Last update: 2019-06-26 03:57    [W:0.066 / U:60.340 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site