[PATCH RFC v3 27/35] arm64: mte: Handle tag storage pages mapped in an MTE VMA

Alexandru Elisei
2024-01-25T16:48:26Z

Tag stoarge pages cannot be tagged. When such a page is mapped in a
MTE-enabled VMA, migrate it out directly and don't try to reserve tag
storage for it.

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 | 11 +++++++++--
3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/mte_tag_storage.h b/arch/arm64/include/asm/mte_tag_storage.h
index 6d0f6ffcfdd6..50bdae94cf71 100644
--- a/arch/arm64/include/asm/mte_tag_storage.h
+++ b/arch/arm64/include/asm/mte_tag_storage.h
@@ -32,6 +32,7 @@ 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_folio_missing_tag_storage(struct folio *folio, struct vm_fault *vmf,
bool *map_pte);
diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c
index 1c8469781870..afe2bb754879 100644
--- a/arch/arm64/kernel/mte_tag_storage.c
+++ b/arch/arm64/kernel/mte_tag_storage.c
@@ -492,6 +492,21 @@ 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 1db3adb6499f..01450ab91a87 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -1014,6 +1014,7 @@ static int replace_folio_with_tagged(struct folio *folio)
vm_fault_t handle_folio_missing_tag_storage(struct folio *folio, struct vm_fault *vmf,
bool *map_pte)
{
+ bool is_tag_storage = page_is_tag_storage(folio_page(folio, 0));
struct vm_area_struct *vma = vmf->vma;
int ret = 0;

@@ -1033,12 +1034,18 @@ vm_fault_t handle_folio_missing_tag_storage(struct folio *folio, struct vm_fault
if (unlikely(is_migrate_isolate_page(folio_page(folio, 0))))
goto out_retry;

- ret = reserve_tag_storage(folio_page(folio, 0), folio_order(folio), GFP_HIGHUSER_MOVABLE);
- if (ret) {
+ if (!is_tag_storage) {
+ ret = reserve_tag_storage(folio_page(folio, 0), folio_order(folio),
+ GFP_HIGHUSER_MOVABLE);
+ if (!ret)
+ goto out_map;
+
/* replace_folio_with_tagged() is expensive, try to avoid it. */
if (fault_flag_allow_retry_first(vmf->flags))
goto out_retry;
+ }

+ if (ret || is_tag_storage) {
replace_folio_with_tagged(folio);
return 0;
}
--
2.43.0