On 29.11.23 12:55, Alexandru Elisei wrote:
Hi,
On Tue, Nov 28, 2023 at 06:55:18PM +0100, David Hildenbrand wrote:
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
Yes, arm64 basically defines PAGE_FAULT_ON_ACCESS as PAGE_NONE |
PTE_TAG_STORAGE_NONE.
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.
Your suggestion from the follow-up reply that an arch should know if it needs to
do something was spot on, arm64 can use the software bit in the translation
table entry for that.
So what you are proposing is this:
* Rename do_numa_page->handle_pte_protnone
* At some point in the do_numa_page (now renamed to handle_pte_protnone) flow,
decide if pte_protnone() has been set for an arch specific reason or because
of automatic NUMA balancing.
* if pte_protnone() has been set by an architecture, then let the architecture
handle the fault.
If I understood you correctly, that's a good idea, and should be easy to
implement.
yes! :)
--
Cheers,
David / dhildenb
