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

Peter Collingbourne
2023-11-28T05:40:01Z

Hi Alexandru,

On Sun, Nov 19, 2023 at 8:59 AM Alexandru Elisei
<alexandru.elisei@arm.com> wrote:
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
> 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