On 10/28/22 13:42, Yicong Yang wrote:
> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
> +{
> + /*
> + * TLB batched flush is proved to be beneficial for systems with large
> + * number of CPUs, especially system with more than 8 CPUs. TLB shutdown
> + * is cheap on small systems which may not need this feature. So use
> + * a threshold for enabling this to avoid potential side effects on
> + * these platforms.
> + */
> + if (num_online_cpus() <= CONFIG_ARM64_NR_CPUS_FOR_BATCHED_TLB)
> + return false;
> +
> +#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI
> + if (unlikely(this_cpu_has_cap(ARM64_WORKAROUND_REPEAT_TLBI)))
> + return false;
> +#endif
should_defer_flush() is immediately followed by set_tlb_ubc_flush_pending() which calls
arch_tlbbatch_add_mm(), triggering the actual TLBI flush via __flush_tlb_page_nosync().
It should be okay to check capability with this_cpu_has_cap() as the entire call chain
here is executed on the same cpu. But just wondering if cpus_have_const_cap() would be
simpler, consistent, and also cost effective ?
Regardless, a comment is needed before the #ifdef block explaining why it does not make
sense to defer/batch when __tlbi()/__tlbi_user() implementation will execute 'dsb(ish)'
between two TLBI instructions to workaround the errata.
> +
> + return true;
> +}
> +
> +static inline void arch_tlbbatch_add_mm(struct arch_tlbflush_unmap_batch *batch,
> + struct mm_struct *mm,
> + unsigned long uaddr)
> +{
> + __flush_tlb_page_nosync(mm, uaddr);
> +}
> +
> +static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
> +{
> + dsb(ish);
> +}
