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.
If I go with the first fix for the page merging, I'll look to defer the zero page initialisation post page_alloc_init_late() in a separate patch.