linux-kernel - Re: [PATCH v1 03/12] mm/rmap: convert make_device_exclusive_range() to make_device

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Message-ID: <2985fbe9-8af8-44c9-bb9e-b3ab3131981a@redhat.com>
Date: Fri, 31 Jan 2025 10:29:57 +0100
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
 nouveau@...ts.freedesktop.org, Andrew Morton <akpm@...ux-foundation.org>,
 Jérôme Glisse <jglisse@...hat.com>,
 Jonathan Corbet <corbet@....net>, Alex Shi <alexs@...nel.org>,
 Yanteng Si <si.yanteng@...ux.dev>, Karol Herbst <kherbst@...hat.com>,
 Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pasha Tatashin <pasha.tatashin@...een.com>, Peter Xu <peterx@...hat.com>,
 Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v1 03/12] mm/rmap: convert make_device_exclusive_range()
 to make_device_exclusive()

On 31.01.25 01:28, Alistair Popple wrote:
> On Thu, Jan 30, 2025 at 04:57:39PM +1100, Alistair Popple wrote:
>> On Wed, Jan 29, 2025 at 12:54:01PM +0100, David Hildenbrand wrote:
> 
> [...]
> 
>>> -int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
>>> -				unsigned long end, struct page **pages,
>>> -				void *owner)
>>> +struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr,
>>> +		void *owner, struct folio **foliop)
>>>   {
>>> -	long npages = (end - start) >> PAGE_SHIFT;
>>> -	long i;
>>> +	struct folio *folio;
>>> +	struct page *page;
>>> +	long npages;
>>> +
>>> +	mmap_assert_locked(mm);
>>>   
>>> -	npages = get_user_pages_remote(mm, start, npages,
>>> +	/*
>>> +	 * Fault in the page writable and try to lock it; note that if the
>>> +	 * address would already be marked for exclusive use by the device,
>>> +	 * the GUP call would undo that first by triggering a fault.
>>> +	 */
>>> +	npages = get_user_pages_remote(mm, addr, 1,
>>>   				       FOLL_GET | FOLL_WRITE | FOLL_SPLIT_PMD,
>>> -				       pages, NULL);
>>> -	if (npages < 0)
>>> -		return npages;
>>> -
>>> -	for (i = 0; i < npages; i++, start += PAGE_SIZE) {
>>> -		struct folio *folio = page_folio(pages[i]);
>>> -		if (PageTail(pages[i]) || !folio_trylock(folio)) {
>>> -			folio_put(folio);
>>> -			pages[i] = NULL;
>>> -			continue;
>>> -		}
>>> +				       &page, NULL);
>>> +	if (npages != 1)
>>> +		return ERR_PTR(npages);
>>> +	folio = page_folio(page);
>>>   
>>> -		if (!folio_make_device_exclusive(folio, mm, start, owner)) {
>>> -			folio_unlock(folio);
>>> -			folio_put(folio);
>>> -			pages[i] = NULL;
>>> -		}
>>> +	if (!folio_test_anon(folio) || folio_test_hugetlb(folio)) {
>>> +		folio_put(folio);
>>> +		return ERR_PTR(-EOPNOTSUPP);
>>> +	}
>>> +
>>> +	if (!folio_trylock(folio)) {
> 
> Actually I think we can make this folio_lock(folio) now. The only reason for
> the trylock was to avoid deadlock between other threads looping over a range
> of folios while holding folio locks which is something the migration code also
> does.

Okay, let me do that in a separate patch. Thanks!

-- 
Cheers,

David / dhildenb