Re: [GIT PULL] arm64 updates for 6.13-rc1

Catalin Marinas
2024-11-28T14:12:22Z

On Wed, Nov 27, 2024 at 05:21:37PM -0800, Yang Shi wrote:
> > > diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
> > > index 87b3f1a25535..ef303a2262c5 100644
> > > --- a/arch/arm64/mm/copypage.c
> > > +++ b/arch/arm64/mm/copypage.c
> > > @@ -30,9 +30,9 @@ void copy_highpage(struct page *to, struct page *from)
> > > if (!system_supports_mte())
> > > return;
> > > - if (folio_test_hugetlb(src) &&
> > > - folio_test_hugetlb_mte_tagged(src)) {
> > > - if (!folio_try_hugetlb_mte_tagging(dst))
> > > + if (folio_test_hugetlb(src)) {
> > > + if (!folio_test_hugetlb_mte_tagged(src) ||
> > > + !folio_try_hugetlb_mte_tagging(dst))
> > > return;
> > > /*
> > I wonder why we had a 'return' here originally rather than a
> > WARN_ON_ONCE() as we do further down for the page case. Do you seen any
> > issue with the hunk below? Destination should be a new folio and not
> > tagged yet:
>
> Yes, I did see problem. Because we copy tags for all sub pages then set
> folio mte tagged when copying the data for the first subpage. The warning
> will be triggered when we copy the second subpage.

Ah, good point, copy_highpage() will be called multiple times for each
subpage but we only do the copying once for the folio.

Now, I wonder whether we should actually defer the tag copying until
copy_page() is called on the head page. This way we can keep the warning
for consistency with the non-compound page case:

diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
index 87b3f1a25535..a86c897017df 100644
--- a/arch/arm64/mm/copypage.c
+++ b/arch/arm64/mm/copypage.c
@@ -30,11 +30,13 @@ void copy_highpage(struct page *to, struct page *from)
if (!system_supports_mte())
return;

- if (folio_test_hugetlb(src) &&
- folio_test_hugetlb_mte_tagged(src)) {
- if (!folio_try_hugetlb_mte_tagging(dst))
+ if (folio_test_hugetlb(src)) {
+ if (!folio_test_hugetlb_mte_tagged(src) ||
+ from != folio_page(src, 0))
return;

+ WARN_ON_ONCE(!folio_try_hugetlb_mte_tagging(dst));
+
/*
* Populate tags for all subpages.
*

--
Catalin