On Tue, Feb 18, 2025 at 02:27:31PM -0800, Dave Hansen wrote:
> On 2/18/25 10:00, Rik van Riel wrote:
> > On Sat, 2025-02-15 at 02:08 +0000, Yosry Ahmed wrote:
> >> So I think what Dave wants (and I agree) is:
> >> if (!broadcast_kernel_range_flush(info))
> >> ipi_kernel_range_flush(info)
> >>
> >> Where ipi_kernel_range_flush() contains old_thing1() and oldthing2().
>
> That's OK-ish. But it still smells of hacking in the new concept without
> refactoring things properly.
>
> Let's logically inline the code that we've got. I think it actually
> ends up looking something like this:
>
> if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
> if (info->end == TLB_FLUSH_ALL) {
> invlpgb_flush_all();
> } else {
> for_each(addr)
> invlpgb_flush_addr_nosync(addr, nr);
> }
> } else {
> if (info->end == TLB_FLUSH_ALL)
> on_each_cpu(do_flush_tlb_all, NULL, 1);
> else
> on_each_cpu(do_kernel_range_flush, info, 1);
> }
>
> Where we've got two inputs:
>
> 1. INVLPGB support (or not)
> 2. TLB_FLUSH_ALL (basically ranged or full flush)
>
> So I think we should group by *one* of those. The above groups by
> INVLPGB support and this groups by TLB_FLUSH_ALL:
>
> if (info->end == TLB_FLUSH_ALL) {
> if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
> invlpgb_flush_all();
> } else {
> on_each_cpu(do_flush_tlb_all, NULL, 1);
> }
> } else {
> if (cpu_feature_enabled(X86_FEATURE_INVLPGB))
> for_each(addr)
> invlpgb_flush_addr_nosync(addr, nr);
> else
> on_each_cpu(do_kernel_range_flush, info, 1);
> }
Yeah an if/else structure is better than using the invlpgb helper and
falling back to IPIs if it returns false, and I also prefer grouping by
the flush scope (range/flush).
Thanks for the illustrations :)
>
> So, if we create some helpers that give some consistent naming:
>
> static tlb_flush_all_ipi(...)
> {
> on_each_cpu(do_flush_tlb_all, NULL, 1);
> }
>
> static tlb_flush_all(...)
> {
> if (cpu_feature_enabled(X86_FEATURE_INVLPGB))
> invlpgb_flush_all(...);
> else
> tlb_flush_all_ipi(...);
> }
>
> and then also create the ranged equivalents (which internally have the
> same cpu_feature_enabled() check):
>
> tlb_flush_range_ipi(...)
> invlpgb_flush_range(...)
>
> Then we can have the top-level code be:
>
> if (info->end == TLB_FLUSH_ALL)
> tlb_flush_all(info);
> else
> tlb_flush_range(info);
>
> That actually looks way nicer than what we have today. For bonus points,
> if a third way of flushing the TLB showed up, it would slot right in:
>
> static tlb_flush_all(...)
> {
> if (cpu_feature_enabled(X86_FEATURE_INVLPGB))
> invlpgb_flush_all(...);
> + else if cpu_feature_enabled(X86_FEATURE_RAR))
> + rar_flush_all(...);
> else
> tlb_flush_all_ipi(...);
> }
>
> That's *exactly* the way we want the code to read. At the higher level,
> it's deciding based on the generic thing that *everybody* cares about:
> ranged or full flush. Then, at the lower level, it's deciding how to
> implement that high-level flush concept.
>
