On Thu, May 20, 2021 at 01:25:50PM +0100, Catalin Marinas wrote:

On Thu, May 20, 2021 at 12:55:21PM +0100, Steven Price wrote:

quoted

The problem I hit is one of include dependencies:

is_swap_pte() is defined (as a static inline) in
include/linux/swapops.h. However the definition depends on
pte_none()/pte_present() which are defined in pgtable.h - so there's a
circular dependency.

Open coding is_swap_pte() in set_pte_at() works, but it's a bit ugly.
Any ideas on how to improve on the below?

	if (system_supports_mte() && pte_present(pte) &&
	    pte_access_permitted(pte, false) && !pte_special(pte)) {
		pte_t old_pte = READ_ONCE(*ptep);
		/*
		 * We only need to synchronise if the new PTE has tags enabled
		 * or if swapping in (in which case another mapping may have
		 * set tags in the past even if this PTE isn't tagged).
		 * (!pte_none() && !pte_present()) is an open coded version of
		 * is_swap_pte()
		 */
		if (pte_tagged(pte) || (!pte_none(pte) && !pte_present(pte)))
			mte_sync_tags(old_pte, pte);
	}

That's why I avoided testing my suggestion ;). I think we should just
add !pte_none() in there with a comment that it may be a swap pte and
use the is_swap_pte() again on the mte_sync_tags() path. We already have
the pte_present() check.

Correction - pte_present() checks the new pte only, we need another for
the old pte. So it looks like we'll open-code is_swap_pte().

-- 
Catalin

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