On Thu, Oct 21, 2021 at 08:04:50PM -0700, Andrew Morton wrote:

On Thu, 21 Oct 2021 05:21:07 -0700 Nadav Amit [off-list ref] wrote:

quoted

This patch-set is intended to remove unnecessary TLB flushes. It is
based on feedback from v1 and several bugs I found in v1 myself.

Basically, there are 3 optimizations in this patch-set:
1. Avoiding TLB flushes on change_huge_pmd() that are only needed to
   prevent the A/D bits from changing.
2. Use TLB batching infrastructure to batch flushes across VMAs and
   do better/fewer flushes.
3. Avoid TLB flushes on permission demotion.

Andrea asked for the aforementioned (2) to come after (3), but this
is not simple (specifically since change_prot_numa() needs the number
of pages affected).

[1/5] appears to be a significant fix which should probably be
backported into -stable kernels.  If you agree with this then I suggest
it be prepared as a standalone patch, separate from the other four
patches.  With a cc:stable.

I am confused, 1/5 doesn't actually do *anything*. I also cannot find
any further usage of the introduced X86_BUG_PTE_LEAK.

I'm thinking patch #2 means to have something like:

	if (cpu_feature_enabled(X86_BUG_PTE_LEAK))
		flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);

In the newly minted: pmdp_invalidate_ad(), but alas, nothing there.