On Tue, Jun 25, 2024 at 04:37:17PM -0700, Yang Shi wrote:
> MTE can be supported on ram based filesystem. It is supported on tmpfs.
> There is use case to use MTE on hugetlbfs as well, adding MTE support.
>
> Signed-off-by: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
> ---
> fs/hugetlbfs/inode.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index ecad73a4f713..c34faef62daf 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -110,7 +110,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
> * way when do_mmap unwinds (may be important on powerpc
> * and ia64).
> */
> - vm_flags_set(vma, VM_HUGETLB | VM_DONTEXPAND);
> + vm_flags_set(vma, VM_HUGETLB | VM_DONTEXPAND | VM_MTE_ALLOWED);
> vma->vm_ops = &hugetlb_vm_ops;
Last time I checked, about a year ago, this was not sufficient. One
issue is that there's no arch_clear_hugetlb_flags() implemented by your
patch, leaving PG_arch_{2,3} set on a page. The other issue was that I
initially tried to do this only on the head page but this did not go
well with the folio_copy() -> copy_highpage() which expects the
PG_arch_* flags on each individual page. The alternative was for
arch_clear_hugetlb_flags() to iterate over all the pages in a folio.
I'd also like to see some tests added to
tools/testing/selftest/arm64/mte to exercise MAP_HUGETLB with PROT_MTE:
write/read tags, a series of mman+munmap (mostly to check if old page
flags are still around), force some copy on write. I don't think we
should merge the patch without proper tests.
An untested hunk on top of your changes:
diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index 3954cbd2ff56..5357b00b9087 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -20,7 +20,19 @@ 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);
+ unsigned long i, nr_pages = folio_nr_pages(folio);
+ const unsigned long clear_flags = BIT(PG_dcache_clean) |
+ BIT(PG_arch_2) | BIT(PG_arch_3);
+
+ if (!system_supports_mte()) {
+ clear_bit(PG_dcache_clean, &folio->flags);
+ return;
+ }
+
+ for (i = 0; i < nr_pages; i++) {
+ struct page *page = folio_page(folio, i);
+ page->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;
--
Catalin
