Re: [v2 PATCH 1/2] hugetlb: arm64: add mte support

[David Hildenbrand <david@redhat.com>]

On 21.08.24 20:47, Yang Shi wrote:
> Enable MTE support for hugetlb.
> 
> The MTE page flags will be set on the head page only.  When copying
> hugetlb folio, the tags for all tail pages will be copied when copying
> head page.
> 
> When freeing hugetlb folio, the MTE flags will be cleared.
> 
> Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
> ---
>   arch/arm64/include/asm/hugetlb.h | 11 ++++++++++-
>   arch/arm64/include/asm/mman.h    |  3 ++-
>   arch/arm64/kernel/hibernate.c    |  7 +++++++
>   arch/arm64/kernel/mte.c          | 25 +++++++++++++++++++++++--
>   arch/arm64/kvm/guest.c           | 16 +++++++++++++---
>   arch/arm64/kvm/mmu.c             | 11 +++++++++++
>   arch/arm64/mm/copypage.c         | 25 +++++++++++++++++++++++--
>   fs/hugetlbfs/inode.c             |  2 +-
>   8 files changed, 90 insertions(+), 10 deletions(-)
> 
> v2: * Reimplemented the patch to fix the comments from Catalin.
>      * Added test cases (patch #2) per Catalin.
> 
> diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
> index 293f880865e8..00a1f75d40ee 100644
> --- a/arch/arm64/include/asm/hugetlb.h
> +++ b/arch/arm64/include/asm/hugetlb.h
> @@ -11,6 +11,7 @@
>   #define __ASM_HUGETLB_H
>   
>   #include <asm/cacheflush.h>
> +#include <asm/mte.h>
>   #include <asm/page.h>
>   
>   #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
> @@ -20,7 +21,15 @@ extern bool arch_hugetlb_migration_supported(struct hstate *h);
>   
>   static inline void arch_clear_hugetlb_flags(struct folio *folio)
>   {
> -	clear_bit(PG_dcache_clean, &folio->flags);
> +	const unsigned long clear_flags = BIT(PG_dcache_clean) |
> +		BIT(PG_mte_tagged) | BIT(PG_mte_lock);
> +
> +	if (!system_supports_mte()) {
> +		clear_bit(PG_dcache_clean, &folio->flags);
> +		return;
> +	}
> +
> +	folio->flags &= ~clear_flags;
>   }
>   #define arch_clear_hugetlb_flags arch_clear_hugetlb_flags
>   
> diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
> index 5966ee4a6154..304dfc499e68 100644
> --- a/arch/arm64/include/asm/mman.h
> +++ b/arch/arm64/include/asm/mman.h
> @@ -28,7 +28,8 @@ static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
>   	 * backed by tags-capable memory. The vm_flags may be overridden by a
>   	 * filesystem supporting MTE (RAM-based).
>   	 */
> -	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
> +	if (system_supports_mte() &&
> +	    (flags & (MAP_ANONYMOUS | MAP_HUGETLB)))
>   		return VM_MTE_ALLOWED;
>   
>   	return 0;
> diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
> index 02870beb271e..722e76f29141 100644
> --- a/arch/arm64/kernel/hibernate.c
> +++ b/arch/arm64/kernel/hibernate.c
> @@ -266,10 +266,17 @@ static int swsusp_mte_save_tags(void)
>   		max_zone_pfn = zone_end_pfn(zone);
>   		for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
>   			struct page *page = pfn_to_online_page(pfn);
> +			struct folio *folio;
>   
>   			if (!page)
>   				continue;
>   
> +			folio = page_folio(page);
> +
> +			if (folio_test_hugetlb(folio) &&
> +			    !page_mte_tagged(&folio->page))
> +				continue;

Can we have folio_test_mte_tagged() whereby you make sure that only 
folio_test_hugetlb() uses it for now (VM_WARN_ON_ONCE) and then make 
sure that nobody uses page_mte_tagged() on hugetlb folios (VM_WARN_ON_ONCE)?

Same for folio_set_mte_tagged() and other functions. We could slap a 
"hugetlb" into the function names, but maybe in the future we'll be able 
to use a single flag per folio (I know, it's complicated ...).

-- 
Cheers,

David / dhildenb