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[2003:d8:2f25:bd00:949:b5a9:e02a:f265]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4532e2384cesm139576665e9.16.2025.06.16.04.18.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jun 2025 04:18:59 -0700 (PDT) Message-ID: <8483b457-6044-4174-9190-161f29f2cda5@redhat.com> Date: Mon, 16 Jun 2025 13:18:58 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] vfio/type1: optimize vfio_unpin_pages_remote() for large folio To: lizhe.67@bytedance.com Cc: alex.williamson@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com References: <753caff4-58d6-4d23-ae69-4b909a99aa16@redhat.com> <20250616111353.7964-1-lizhe.67@bytedance.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250616111353.7964-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.06.25 13:13, lizhe.67@bytedance.com wrote: > On Mon, 16 Jun 2025 10:14:23 +0200, david@redhat.com wrote: > >>> drivers/vfio/vfio_iommu_type1.c | 55 +++++++++++++++++++++++++++------ >>> 1 file changed, 46 insertions(+), 9 deletions(-) >>> >>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c >>> index e952bf8bdfab..09ecc546ece8 100644 >>> --- a/drivers/vfio/vfio_iommu_type1.c >>> +++ b/drivers/vfio/vfio_iommu_type1.c >>> @@ -469,17 +469,28 @@ static bool is_invalid_reserved_pfn(unsigned long pfn) >>> return true; >>> } >>> >>> -static int put_pfn(unsigned long pfn, int prot) >>> +static inline void _put_pfns(struct page *page, int npages, int prot) >>> { >>> - if (!is_invalid_reserved_pfn(pfn)) { >>> - struct page *page = pfn_to_page(pfn); >>> + unpin_user_page_range_dirty_lock(page, npages, prot & IOMMU_WRITE); >>> +} >>> >>> - unpin_user_pages_dirty_lock(&page, 1, prot & IOMMU_WRITE); >>> - return 1; >>> +/* >>> + * The caller must ensure that these npages PFNs belong to the same folio. >>> + */ >>> +static inline int put_pfns(unsigned long pfn, int npages, int prot) >>> +{ >>> + if (!is_invalid_reserved_pfn(pfn)) { >>> + _put_pfns(pfn_to_page(pfn), npages, prot); >>> + return npages; >>> } >>> return 0; >>> } >>> >>> +static inline int put_pfn(unsigned long pfn, int prot) >>> +{ >>> + return put_pfns(pfn, 1, prot); >>> +} >>> + >>> #define VFIO_BATCH_MAX_CAPACITY (PAGE_SIZE / sizeof(struct page *)) >>> >>> static void __vfio_batch_init(struct vfio_batch *batch, bool single) >>> @@ -806,11 +817,37 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova, >>> bool do_accounting) >>> { >>> long unlocked = 0, locked = vpfn_pages(dma, iova, npage); >>> - long i; >>> >>> - for (i = 0; i < npage; i++) >>> - if (put_pfn(pfn++, dma->prot)) >>> - unlocked++; >>> + while (npage) { >>> + long nr_pages = 1; >>> + >>> + if (!is_invalid_reserved_pfn(pfn)) { >>> + struct page *page = pfn_to_page(pfn); >>> + struct folio *folio = page_folio(page); >>> + long folio_pages_num = folio_nr_pages(folio); >>> + >>> + /* >>> + * For a folio, it represents a physically >>> + * contiguous set of bytes, and all of its pages >>> + * share the same invalid/reserved state. >>> + * >>> + * Here, our PFNs are contiguous. Therefore, if we >>> + * detect that the current PFN belongs to a large >>> + * folio, we can batch the operations for the next >>> + * nr_pages PFNs. >>> + */ >>> + if (folio_pages_num > 1) >>> + nr_pages = min_t(long, npage, >>> + folio_pages_num - >>> + folio_page_idx(folio, page)); >>> + >>> + _put_pfns(page, nr_pages, dma->prot); >> >> >> This is sneaky. You interpret the page pointer a an actual page array, >> assuming that it would give you the right values when advancing nr_pages >> in that array. >> >> This is mostly true, but with !CONFIG_SPARSEMEM_VMEMMAP it is not >> universally true for very large folios (e.g., in a 1 GiB hugetlb folio >> when we cross the 128 MiB mark on x86). >> >> Not sure if that could already trigger here, but it is subtle. > > As previously mentioned in the email, the code here functions > correctly. > >>> + unlocked += nr_pages; >> >> We could do slightly better here, as we already have the folio. We would >> add a unpin_user_folio_dirty_locked() similar to unpin_user_folio(). >> >> Instead of _put_pfns, we would be calling >> >> unpin_user_folio_dirty_locked(folio, nr_pages, dma->prot & IOMMU_WRITE); > > Thank you so much for your suggestion. Does this implementation of > unpin_user_folio_dirty_locked() look viable to you? > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index fdda6b16263b..567c9dae9088 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1689,6 +1689,8 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages, > bool make_dirty); > void unpin_user_pages(struct page **pages, unsigned long npages); > void unpin_user_folio(struct folio *folio, unsigned long npages); > +void unpin_user_folio_dirty_locked(struct folio *folio, > + unsigned long npages, bool make_dirty); > void unpin_folios(struct folio **folios, unsigned long nfolios); > > static inline bool is_cow_mapping(vm_flags_t flags) > diff --git a/mm/gup.c b/mm/gup.c > index 84461d384ae2..2f1e14a79463 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -360,11 +360,8 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages, > > for (i = 0; i < npages; i += nr) { > folio = gup_folio_range_next(page, npages, i, &nr); > - if (make_dirty && !folio_test_dirty(folio)) { > - folio_lock(folio); > - folio_mark_dirty(folio); > - folio_unlock(folio); > - } > + if (make_dirty && !folio_test_dirty(folio)) > + folio_mark_dirty_lock(folio); > gup_put_folio(folio, nr, FOLL_PIN); We can call unpin_user_folio_dirty_locked(). :) > } > } > @@ -435,6 +432,26 @@ void unpin_user_folio(struct folio *folio, unsigned long npages) > } > EXPORT_SYMBOL(unpin_user_folio); > > +/** > + * unpin_user_folio_dirty_locked() - release pages of a folio and > + * optionally dirty "conditionally mark a folio dirty and unpin it" Because that's the sequence in which it is done. > + * > + * @folio: pointer to folio to be released > + * @npages: number of pages of same folio Can we change that to "nrefs" or rather "npins"? > + * @make_dirty: whether to mark the folio dirty > + * > + * Mark the folio as being modified if @make_dirty is true. Then > + * release npages of the folio. Similarly, adjust the doc here. > + */ > +void unpin_user_folio_dirty_locked(struct folio *folio, > + unsigned long npages, bool make_dirty) > +{ > + if (make_dirty && !folio_test_dirty(folio)) > + folio_mark_dirty_lock(folio); > + gup_put_folio(folio, npages, FOLL_PIN); > +} > +EXPORT_SYMBOL(unpin_user_folio_dirty_locked); Yes, should probably go into a separate cleanup patch. -- Cheers, David / dhildenb