On Wed, Sep 24, 2025 at 11:13:18AM +0200, David Hildenbrand wrote:
On 24.09.25 10:50, Catalin Marinas wrote:
On Wed, Sep 24, 2025 at 10:49:27AM +0800, Lance Yang wrote:
On 2025/9/24 00:14, Catalin Marinas wrote:
So alternative patch that also fixes the deferred struct page init (on the assumptions that the zero page is always mapped as pte_special():
I can confirm that this alternative patch also works correctly; my tests for MTE all pass ;)
Thanks Lance for testing. I'll post one of the variants today.
This looks like a better fix since it solves the boot hang issue too.
In principle, yes, until I tracked down why I changed it in the first place - 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page"). ptrace() can read tags from PROT_MTE mappings and we want to allow reading zeroes as well if the page points to the zero page. Not flagging the page as PG_mte_tagged caused issues.
I can change the logic in the ptrace() code, I just need to figure out what happens to the huge zero page. Ideally we should treat both in the same way but, AFAICT, we don't use pmd_mkspecial() on the huge zero page, so it gets flagged with PG_mte_tagged.
I changed that recently :) The huge zero folio will now always have pmd_special() set.
Oh, which commit was this? It means that we can end up with uninitialised tags if we have a PROT_MTE huge zero page since set_pmd_at/set_pte_at() skips mte_sync_tags().