Re: [PATCH v13 06/14] x86/mm: use broadcast TLB flushing for page reclaim TLB flushing

Borislav Petkov
2025-02-24T13:27:43Z

On Sun, Feb 23, 2025 at 02:48:56PM -0500, Rik van Riel wrote:
> In the page reclaim code, we only track the CPU(s) where the TLB needs
> to be flushed, rather than all the individual mappings that may be getting
> invalidated.
>
> Use broadcast TLB flushing when that is available.
>
> This is a temporary hack to ensure that the PCID context for
> tasks in the next patch gets properly flushed from the page

There's no "next patch" in git - just merge this three-liner with the next
one.

> reclaim code, because the IPI based flushing in arch_tlbbatch_flush
> only flushes the currently loaded TLB context on each CPU.
>
> Patch 10 replaces this with the actual mechanism used to do

Same. No "patch 10" in git.

> broadcast TLB flushing from the page reclaim code.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Tested-by: Manali Shukla <Manali.Shukla@amd.com>
> Tested-by: Brendan Jackman <jackmanb@google.com>
> Tested-by: Michael Kelley <mhklinux@outlook.com>
> ---
> arch/x86/mm/tlb.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 2d7ed0fda61f..16839651f67f 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -1326,7 +1326,9 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
> * a local TLB flush is needed. Optimize this use-case by calling
> * flush_tlb_func_local() directly in this case.
> */
> - if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) {
> + if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
> + invlpgb_flush_all_nonglobals();

I'm confused. The docs say rAX needs to be 0x6 to do "Invalidate all TLB
entries that match {ASID, PCID} excluding Global". But you're calling INVLPGB
with rAX==0 and the APM doesn't say what this does.

I'm guessing you want this to mean invalidate all non-globals for any ASID and
PCID. So I muss be missing the place in the docs where it says so...

Hmmm?

--
Regards/Gruss,
Boris.