Re: [PATCH v2 4/4] arm64: mte: Add mte_clear_folio_tags()

[Lorenzo Stoakes (ARM)]

On Wed, Oct 21, 2026 at 12:07:00PM +0100, Fuad Tabba wrote:
> mte_sync_tags(), sanitise_mte_tags() and kvm_vm_ioctl_mte_copy_tags()
> each open-code the loop that clears the tags of every page in a hugetlb
> folio. Add mte_clear_folio_tags() and use it in all three.
> kvm_vm_ioctl_mte_copy_tags() then tests for hugetlb first, as it does
> where it sets the tagged flag below.
>
> No functional change intended.
>
> Suggested-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
> Signed-off-by: Fuad Tabba <fuad.tabba@xxxxxxxxx>

Great LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
>  arch/arm64/include/asm/mte.h |  4 ++++
>  arch/arm64/kernel/mte.c      | 15 ++++++++++-----
>  arch/arm64/kvm/guest.c       | 10 +++++-----
>  arch/arm64/kvm/mmu.c         |  3 +--
>  4 files changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
> index 7f7b97e099968..5a2d2814c0416 100644
> --- a/arch/arm64/include/asm/mte.h
> +++ b/arch/arm64/include/asm/mte.h
> @@ -96,6 +96,7 @@ static inline bool try_page_mte_tagging(struct page *page)
>  }
>
>  void mte_zero_clear_page_tags(void *addr);
> +void mte_clear_folio_tags(struct folio *folio);
>  void mte_sync_tags(pte_t pte, unsigned int nr_pages);
>  void mte_copy_page_tags(void *kto, const void *kfrom);
>  void mte_thread_init_user(void);
> @@ -128,6 +129,9 @@ static inline bool try_page_mte_tagging(struct page *page)
>  static inline void mte_zero_clear_page_tags(void *addr)
>  {
>  }
> +static inline void mte_clear_folio_tags(struct folio *folio)
> +{
> +}
>  static inline void mte_sync_tags(pte_t pte, unsigned int nr_pages)
>  {
>  }
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index 1a9aad6ef22a0..fb2598f8c0ccd 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -36,6 +36,14 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
>  EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode);
>  #endif
>
> +void mte_clear_folio_tags(struct folio *folio)
> +{
> +	unsigned long i;
> +
> +	for (i = 0; i < folio_nr_pages(folio); i++)
> +		mte_clear_page_tags(page_address(folio_page(folio, i)));
> +}
> +
>  void mte_sync_tags(pte_t pte, unsigned int nr_pages)
>  {
>  	struct page *page = pte_page(pte);
> @@ -43,12 +51,9 @@ void mte_sync_tags(pte_t pte, unsigned int nr_pages)
>  	unsigned long i;
>
>  	if (folio_test_hugetlb(folio)) {
> -		unsigned long nr = folio_nr_pages(folio);
> -
> -		/* Hugetlb MTE flags are set for head page only */
> +		/* A hugetlb folio is marked tagged as a whole, so clear every page */
>  		if (folio_try_hugetlb_mte_tagging(folio)) {
> -			for (i = 0; i < nr; i++, page++)
> -				mte_clear_page_tags(page_address(page));
> +			mte_clear_folio_tags(folio);
>  			folio_set_hugetlb_mte_tagged(folio);
>  		}
>
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index cda655fbff657..c75466384f8ac 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1012,7 +1012,6 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>  		void *maddr;
>  		unsigned long num_tags;
>  		struct folio *folio;
> -		unsigned long i;
>
>  		if (!page) {
>  			ret = -EFAULT;
> @@ -1046,11 +1045,12 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>  			 * tags. A hugetlb folio is marked tagged as a whole,
>  			 * so its first tagging clears every page.
>  			 */
> -			if (!folio_test_hugetlb(folio))
> +			if (folio_test_hugetlb(folio)) {
> +				if (folio_try_hugetlb_mte_tagging(folio))
> +					mte_clear_folio_tags(folio);
> +			} else {
>  				try_page_mte_tagging(page);
> -			else if (folio_try_hugetlb_mte_tagging(folio))
> -				for (i = 0; i < folio_nr_pages(folio); i++)
> -					mte_clear_page_tags(page_address(folio_page(folio, i)));
> +			}
>  			num_tags = mte_copy_tags_from_user(maddr, tags,
>  							MTE_GRANULES_PER_PAGE);
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 6e10aa9913d71..f8139c0a54deb 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1514,8 +1514,7 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
>  	if (folio_test_hugetlb(folio)) {
>  		/* A hugetlb folio is marked tagged as a whole, so clear every page */
>  		if (folio_try_hugetlb_mte_tagging(folio)) {
> -			for (i = 0; i < folio_nr_pages(folio); i++)
> -				mte_clear_page_tags(page_address(folio_page(folio, i)));
> +			mte_clear_folio_tags(folio);
>  			folio_set_hugetlb_mte_tagged(folio);
>  		}
>  		return;
> --
> 2.47.3
>

--
Cheers, Lorenzo