[PATCH] arm64: mte: Fix copy_highpage() warning on hugetlb folios

[Yang Shi]

On 12/4/24 9:50 AM, Catalin Marinas wrote:
> Commit 25c17c4b55de ("hugetlb: arm64: add mte support") improved the
> copy_highpage() function to update the tags in the destination hugetlb
> folio. However, when the source folio isn't tagged, the code takes the
> non-hugetlb path where try_page_mte_tagging() warns as the destination
> is a hugetlb folio:
>
>    WARNING: CPU: 0 PID: 363 at arch/arm64/include/asm/mte.h:58 copy_highpage+0x1d4/0x2d8
>    [...]
>    pc : copy_highpage+0x1d4/0x2d8
>    lr : copy_highpage+0x78/0x2d8
>    [...]
>    Call trace:
>     copy_highpage+0x1d4/0x2d8 (P)
>     copy_highpage+0x78/0x2d8 (L)
>     copy_user_highpage+0x20/0x48
>     copy_user_large_folio+0x1bc/0x268
>     hugetlb_wp+0x190/0x860
>     hugetlb_fault+0xa28/0xc10
>     handle_mm_fault+0x2a0/0x2c0
>     do_page_fault+0x12c/0x578
>     do_mem_abort+0x4c/0xa8
>     el0_da+0x44/0xb0
>     el0t_64_sync_handler+0xc4/0x138
>     el0t_64_sync+0x198/0x1a0
>
> Change the check for the tagged status of the source folio so that it
> does not fall through the non-hugetlb case. In addition, only perform
> the copy (for the full folio) if the source page is the folio head and
> warn if the destination folio is already tagged, for symmetry with the
> non-hugetlb case.
>
> Fixes: 25c17c4b55de ("hugetlb: arm64: add mte support")
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> Reported-by: Sasha Levin <sashal at kernel.org>
> Cc: Yang Shi <yang at os.amperecomputing.com>
> Cc: David Hildenbrand <david at redhat.com>
> Cc: Will Deacon <will at kernel.org>
> Link: https://lore.kernel.org/r/Z0STR6VLt2MCalnY@sashalap

Thanks for fixing this. Reviewed-by: Yang Shi <yang at os.amperecomputing.com>

> ---
>   arch/arm64/mm/copypage.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> 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.
>   		 *