On 03.07.24 02:20, Yang Shi wrote:
On 7/2/24 6:09 AM, David Hildenbrand wrote:
On 02.07.24 14:34, Catalin Marinas wrote:
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.
This would likely also add a blocker for
ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP on arm64 (no idea if there are now
ways to move forward with that now, or if we are still not sure if we
can actually add support), correct?
IIUC, it is not. We just need to guarantee each subpage has
PG_mte_tagged flag and allocated tags. The HVO just maps the 7 vmemmap
pages for sub pages to the first page, they still see the flag and the
space for tag is not impacted, right? Did I miss something?
In the R/O vmemmap optimization we won't be able to modify the flags of
the double-mapped vmemmap pages via the double mappings.
Of course, we could find HVO-specific ways to only modify the flags of
the first vmemmap page, but it does sound wrong ...
Really, the question is if we can have a per-folio flag for hugetlb
instead and avoid all that?
--
Cheers,
David / dhildenb
