[PATCH] arm64: mte: Do not flag the zero page as PG_mte_tagged

[Will Deacon]

On Wed, 24 Sep 2025 13:31:22 +0100, Catalin Marinas wrote:
> Commit 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to the
> zero page") attempted to fix ptrace() reading of tags from the zero page
> by marking it as PG_mte_tagged during cpu_enable_mte(). The same commit
> also changed the ptrace() tag access permission check to the VM_MTE vma
> flag while turning the page flag test into a WARN_ON_ONCE().
> 
> Attempting to set the PG_mte_tagged flag early with
> CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled may either hang (after commit
> d77e59a8fccd "arm64: mte: Lock a page for MTE tag initialisation") or
> have the flags cleared later during page_alloc_init_late(). In addition,
> pages_identical() -> memcmp_pages() will reject any comparison with the
> zero page as it is marked as tagged.
> 
> [...]

Applied to arm64 (for-next/core), thanks!

[1/1] arm64: mte: Do not flag the zero page as PG_mte_tagged
      https://git.kernel.org/arm64/c/f620d66af316

Cheers,
-- 
Will

https://fixes.arm64.dev
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