Re: [PATCH v3 3/5] x86/mm: Optionally flush L1D on context switch

[Thomas Gleixner]

On Fri, Nov 27 2020 at 17:59, Balbir Singh wrote:
>  
> +     /*
> +      * Flush only if SMT is disabled as per the contract, which is checked
> +      * when the feature is enabled.
> +      */
> +     if (sched_smt_active() && !this_cpu_read(cpu_info.smt_active) &&
> +             (prev_mm & LAST_USER_MM_L1D_FLUSH))
> +             l1d_flush_hw();

So if SMT is completely disabled then no flush? Shouldn't the logic be:

    if ((!sched_smt_active() || !this_cpu_read(cpu_info.smt_active) &&
         (prev_mm & LAST_USER_MM_L1D_FLUSH))

Hmm?

But that's bad, because it's lot's of conditions to evaluate for every
switch_mm where most of them are not interested in it at all.

Let me read through the rest of the pile.

Thanks,

        tglx