arm64: mte: Do not warn if the page is already tagged in copy_highpage()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: arm64: mte: Do not warn if the page is already tagged in copy_highpage() The arm64 copy_highpage() assumes that the destination page is newly allocated and not MTE-tagged (PG_mte_tagged unset) and warns accordingly. However, following commit 060913999d7a ("mm: migrate: support poisoned recover from migrate folio"), folio_mc_copy() is called before __folio_migrate_mapping(). If the latter fails (-EAGAIN), the copy will be done again to the same destination page. Since copy_highpage() already set the PG_mte_tagged flag, this second copy will warn. Replace the WARN_ON_ONCE(page already tagged) in the arm64 copy_highpage() with a comment.

References

• https://git.kernel.org/stable/c/5ff5765a1fc526f07d3bbaedb061d970eb13bcf4
• https://git.kernel.org/stable/c/0bbf3fc6e9211fce9889fe8efbb89c220504d617
• https://git.kernel.org/stable/c/b98c94eed4a975e0c80b7e90a649a46967376f58