Re: [PATCH v1 1/2] mm/hugetlb: fix hugetlb not supporting write-notify

From: David Hildenbrand <david@redhat.com>
To: Mike Kravetz <mike.kravetz@oracle.com>, Peter Xu <peterx@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Muchun Song <songmuchun@bytedance.com>,
	Peter Feiner <pfeiner@google.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v1 1/2] mm/hugetlb: fix hugetlb not supporting write-notify
Date: Fri, 5 Aug 2022 20:25:37 +0200	[thread overview]
Message-ID: <c2a3b903-099c-4b79-6923-8b288d404c51@redhat.com> (raw)
In-Reply-To: <Yu1gHnpKRZBhSTZB@monkey>

On 05.08.22 20:23, Mike Kravetz wrote:
> On 08/05/22 14:14, Peter Xu wrote:
>> On Fri, Aug 05, 2022 at 01:03:28PM +0200, David Hildenbrand wrote:
>>> diff --git a/mm/mmap.c b/mm/mmap.c
>>> index 61e6135c54ef..462a6b0344ac 100644
>>> --- a/mm/mmap.c
>>> +++ b/mm/mmap.c
>>> @@ -1683,6 +1683,13 @@ int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
>>>  	if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
>>>  		return 0;
>>>  
>>> +	/*
>>> +	 * Hugetlb does not require/support writenotify; especially, it does not
>>> +	 * support softdirty tracking.
>>> +	 */
>>> +	if (is_vm_hugetlb_page(vma))
>>> +		return 0;
>>
>> I'm kind of confused here..  you seems to be fixing up soft-dirty for
>> hugetlb but here it's explicitly forbidden.
>>
>> Could you explain a bit more on why this patch is needed if (assume
>> there'll be a working) patch 2 being provided?
>>
> 
> No comments on the patch, but ...
> 
> Since it required little thought, I ran the test program on next-20220802 and
> was surprised that the issue did not recreate.  Even added a simple printk
> to make sure we were getting into vma_wants_writenotify with a hugetlb vma.
> We were.

... does your config have CONFIG_MEM_SOFT_DIRTY enabled?

-- 
Thanks,

David / dhildenb