Messages in this thread | | | Date | Thu, 5 Nov 2020 15:59:00 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH v8 28/43] arm64: mte: Reset the page tag in page->flags |
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On Thu, Nov 05, 2020 at 12:18:43AM +0100, Andrey Konovalov wrote: > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index 8f99c65837fd..06ba6c923ab7 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -34,6 +34,7 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > return; > } > > + page_kasan_tag_reset(page); > mte_clear_page_tags(page_address(page));
I think we need an smp_wmb() between setting the flags and clearing the actual tags. If another threads reads page->flags and builds a tagged address out of it (see page_to_virt) there's an address dependency to the actual memory access. However, on the current thread, we don't guarantee that the new page->flags are visible before the tags were updated.
> } > > diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c > index 70a71f38b6a9..348f4627da08 100644 > --- a/arch/arm64/mm/copypage.c > +++ b/arch/arm64/mm/copypage.c > @@ -22,6 +22,7 @@ void copy_highpage(struct page *to, struct page *from) > copy_page(kto, kfrom); > > if (system_supports_mte() && test_bit(PG_mte_tagged, &from->flags)) { > + page_kasan_tag_reset(to); > set_bit(PG_mte_tagged, &to->flags); > mte_copy_page_tags(kto, kfrom);
Nitpick: move page_kasan_tag_reset() just above mte_copy_page_tags() for consistency with the other places where PG_mte_tagged is set before or after the actual tag setting.
> } > diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c > index c52c1847079c..0e7eccbe598a 100644 > --- a/arch/arm64/mm/mteswap.c > +++ b/arch/arm64/mm/mteswap.c > @@ -53,6 +53,7 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page) > if (!tags) > return false; > > + page_kasan_tag_reset(page); > mte_restore_page_tags(page_address(page), tags);
There is another mte_restore_page_tags() caller in hibernate.c. That one doesn't need page_kasan_tag_reset() since the page->flags would have been already restored but please add a comment in that file why its not needed.
-- Catalin
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