Re: [PATCH RFC v2 21/27] mm: arm64: Handle tag storage pages mapped before mprotect(PROT_MTE)

[Peter Collingbourne]

Hi Alexandru,

On Sun, Nov 19, 2023 at 8:59 AM Alexandru Elisei
<alexandru.elisei@xxxxxxx> wrote:
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
>  arch/arm64/include/asm/mte_tag_storage.h |  1 +
>  arch/arm64/kernel/mte_tag_storage.c      | 15 +++++++
>  arch/arm64/mm/fault.c                    | 55 ++++++++++++++++++++++++
>  include/linux/migrate.h                  |  8 +++-
>  include/linux/migrate_mode.h             |  1 +
>  mm/internal.h                            |  6 ---
>  6 files changed, 78 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/include/asm/mte_tag_storage.h b/arch/arm64/include/asm/mte_tag_storage.h
> index b97406d369ce..6a8b19a6a758 100644
> --- a/arch/arm64/include/asm/mte_tag_storage.h
> +++ b/arch/arm64/include/asm/mte_tag_storage.h
> @@ -33,6 +33,7 @@ int reserve_tag_storage(struct page *page, int order, gfp_t gfp);
>  void free_tag_storage(struct page *page, int order);
>
>  bool page_tag_storage_reserved(struct page *page);
> +bool page_is_tag_storage(struct page *page);
>
>  vm_fault_t handle_page_missing_tag_storage(struct vm_fault *vmf);
>  vm_fault_t handle_huge_page_missing_tag_storage(struct vm_fault *vmf);
> diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c
> index a1cc239f7211..5096ce859136 100644
> --- a/arch/arm64/kernel/mte_tag_storage.c
> +++ b/arch/arm64/kernel/mte_tag_storage.c
> @@ -500,6 +500,21 @@ bool page_tag_storage_reserved(struct page *page)
>         return test_bit(PG_tag_storage_reserved, &page->flags);
>  }
>
> +bool page_is_tag_storage(struct page *page)
> +{
> +       unsigned long pfn = page_to_pfn(page);
> +       struct range *tag_range;
> +       int i;
> +
> +       for (i = 0; i < num_tag_regions; i++) {
> +               tag_range = &tag_regions[i].tag_range;
> +               if (tag_range->start <= pfn && pfn <= tag_range->end)
> +                       return true;
> +       }
> +
> +       return false;
> +}
> +
>  int reserve_tag_storage(struct page *page, int order, gfp_t gfp)
>  {
>         unsigned long start_block, end_block;
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 6730a0812a24..964c5ae161a3 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -12,6 +12,7 @@
>  #include <linux/extable.h>
>  #include <linux/kfence.h>
>  #include <linux/signal.h>
> +#include <linux/migrate.h>
>  #include <linux/mm.h>
>  #include <linux/hardirq.h>
>  #include <linux/init.h>
> @@ -956,6 +957,50 @@ void tag_clear_highpage(struct page *page)
>  }
>
>  #ifdef CONFIG_ARM64_MTE_TAG_STORAGE
> +
> +#define MR_TAGGED_TAG_STORAGE  MR_ARCH_1
> +
> +extern bool isolate_lru_page(struct page *page);
> +extern void putback_movable_pages(struct list_head *l);

Could we move these declarations to a non-mm-internal header and
#include it instead of manually declaring them here?

> +
> +/* Returns with the page reference dropped. */
> +static void migrate_tag_storage_page(struct page *page)
> +{
> +       struct migration_target_control mtc = {
> +               .nid = NUMA_NO_NODE,
> +               .gfp_mask = GFP_HIGHUSER_MOVABLE | __GFP_TAGGED,
> +       };
> +       unsigned long i, nr_pages = compound_nr(page);
> +       LIST_HEAD(pagelist);
> +       int ret, tries;
> +
> +       lru_cache_disable();
> +
> +       for (i = 0; i < nr_pages; i++) {
> +               if (!isolate_lru_page(page + i)) {
> +                       ret = -EAGAIN;
> +                       goto out;
> +               }
> +               /* Isolate just grabbed another reference, drop ours. */
> +               put_page(page + i);
> +               list_add_tail(&(page + i)->lru, &pagelist);
> +       }
> +
> +       tries = 5;
> +       while (tries--) {
> +               ret = migrate_pages(&pagelist, alloc_migration_target, NULL, (unsigned long)&mtc,
> +                                   MIGRATE_SYNC, MR_TAGGED_TAG_STORAGE, NULL);
> +               if (ret == 0 || ret != -EBUSY)

This could be simplified to:

if (ret != -EBUSY)

Peter