Hi Catalin,

On 11/5/20 3:59 PM, Catalin Marinas wrote:

On Thu, Nov 05, 2020 at 12:18:43AM +0100, Andrey Konovalov wrote:

quoted

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.

Indeed, and I will add a comment as well to explain why.

quoted

 }
 

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.

Fine, I will add it to the next iteration.

quoted

 	}

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);

I just realized based on your comment above that we need smp_wmb() here as well.
I will add it with a comment as well.

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.

Yes I will do, I agree on the reasoning, I will report it in the comments.

-- 
Regards,
Vincenzo

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