linux-kernel - Re: [PATCH] hugetlbfs: add MTE support

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Date: Tue, 2 Jul 2024 15:09:28 +0200
From: David Hildenbrand <david@...hat.com>
To: Catalin Marinas <catalin.marinas@....com>,
 Yang Shi <yang@...amperecomputing.com>
Cc: muchun.song@...ux.dev, will@...nel.org, akpm@...ux-foundation.org,
 linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hugetlbfs: add MTE support

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@...amperecomputing.com>
>> ---
>>   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?


-- 
Cheers,

David / dhildenb