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Message-ID: <1c79ad05-cb52-4820-b2aa-bbe07ff82b19@redhat.com>
Date: Tue, 28 Nov 2023 18:55:18 +0100
From: David Hildenbrand <david@...hat.com>
To: Alexandru Elisei <alexandru.elisei@....com>,
catalin.marinas@....com, will@...nel.org, oliver.upton@...ux.dev,
maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
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bristot@...hat.com, vschneid@...hat.com, mhiramat@...nel.org,
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Cc: pcc@...gle.com, steven.price@....com, anshuman.khandual@....com,
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hyesoo.yu@...sung.com, linux-arm-kernel@...ts.infradead.org,
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Subject: Re: [PATCH RFC v2 19/27] mm: mprotect: Introduce PAGE_FAULT_ON_ACCESS
for mprotect(PROT_MTE)
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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