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

Thomas Gleixner
2020-12-04T21:22:08Z

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