Messages in this thread | | | Date | Mon, 12 Oct 2020 12:45:08 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/alternative: don't call text_poke() in lazy TLB mode |
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On Mon, Oct 12, 2020 at 12:26:06PM +0200, Jürgen Groß wrote:
> > > @@ -807,6 +807,15 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) > > > temp_mm_state_t temp_state; > > > lockdep_assert_irqs_disabled(); > > > + > > > + /* > > > + * Make sure not to be in TLB lazy mode, as otherwise we'll end up > > > + * with a stale address space WITHOUT being in lazy mode after > > > + * restoring the previous mm. > > > + */ > > > + if (this_cpu_read(cpu_tlbstate.is_lazy)) > > > + leave_mm(smp_processor_id()); > > > + > > > temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); > > > switch_mm_irqs_off(NULL, mm, current); > > > > Would it make sense to write it like: > > > > this_state.mm = this_cpu_read(cpu_tlbstate.is_lazy) ? > > &init_mm : this_cpu_read(cpu_tlbstate.loaded_mm); > > > > Possibly with that wrapped in a conveniently named helper function. > > Fine with me, but I don't think it matters that much. > > For each batch of text_poke() it will be hit only once, and I'm not sure > it is really a good idea to use the knowledge that leave_mm() is just a > switch to init_mm here.
Yeah, I'm not sure either. But it's something I came up with when looking at all this.
Andy, what's your preference?
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