From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
To: Fuad Tabba <fuad.tabba@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>, Oliver Upton <oupton@kernel.org>,
kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
Joey Gouly <joey.gouly@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Steffen Eiden <seiden@linux.ibm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Steven Price <steven.price@arm.com>,
Yang Shi <yang@os.amperecomputing.com>,
David Hildenbrand <david@kernel.org>,
Fuad Tabba <tabba@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/4] arm64: mte: Add mte_clear_folio_tags()
Date: Wed, 21 Oct 2026 13:28:42 +0100 [thread overview]
Message-ID: <ativTPb95ZxK2_ho@gremlin> (raw)
In-Reply-To: <20261021110700.493315-5-fuad.tabba@linux.dev>
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@kernel.org>
> Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
Great LGTM so:
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> ---
> 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
prev parent reply other threads:[~2026-10-21 12:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 11:06 [PATCH v2 0/4] KVM: arm64: Fix stale MTE tags reaching a guest Fuad Tabba
2026-10-21 11:06 ` [PATCH v2 1/4] KVM: arm64: Clear the whole hugetlb folio when sanitising MTE tags Fuad Tabba
2026-10-21 11:06 ` [PATCH v2 2/4] KVM: arm64: Clear the whole hugetlb folio when storing " Fuad Tabba
2026-10-21 11:06 ` [PATCH v2 3/4] KVM: arm64: Sanitise MTE tags when a permission fault installs a mapping Fuad Tabba
2026-10-21 11:07 ` [PATCH v2 4/4] arm64: mte: Add mte_clear_folio_tags() Fuad Tabba
2026-10-21 12:28 ` Lorenzo Stoakes (ARM) [this message]
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