Re: [PATCH RFC v2 19/27] mm: mprotect: Introduce PAGE_FAULT_ON_ACCESS for mprotect(PROT_MTE)

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On 19.11.23 17:57, Alexandru Elisei wrote:
To enable tagging on a memory range, userspace can use mprotect() with the
PROT_MTE access flag. Pages already mapped in the VMA don't have the
associated tag storage block reserved, so mark the PTEs as
PAGE_FAULT_ON_ACCESS to trigger a fault next time they are accessed, and
reserve the tag storage on the fault path.

That sounds alot like fake PROT_NONE. Would there be a way to unify hat handling and simply reuse pte_protnone()? For example, could we special case on VMA flags?

Like, don't do NUMA hinting in these special VMAs. Then, have something like:

if (pte_protnone(vmf->orig_pte))
	return handle_pte_protnone(vmf);

In there, special case on the VMA flags.

I *suspect* that handle_page_missing_tag_storage() stole (sorry :P) some code from the prot_none handling path. At least the recovery path and writability handling looks like it better be located shared in handle_pte_protnone() as well.

That might take some magic out of this patch.

--
Cheers,

David / dhildenb





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