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(p200300d82f42b000db8b7655f60f812b.dip0.t-ipconnect.de. [2003:d8:2f42:b000:db8b:7655:f60f:812b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e0157d68esm12986065e9.6.2025.09.11.05.15.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 05:15:53 -0700 (PDT) Message-ID: <17e3c19e-0719-4643-8db8-cf8c5b5aa022@redhat.com> Date: Thu, 11 Sep 2025 14:15:51 +0200 Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v5 02/15] mm/huge_memory: add device-private THP support to PMD operations To: Balbir Singh , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: damon@lists.linux.dev, dri-devel@lists.freedesktop.org, Andrew Morton , Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Oscar Salvador , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , =?UTF-8?Q?Mika_Penttil=C3=A4?= , Matthew Brost , Francois Dugast References: <20250908000448.180088-1-balbirs@nvidia.com> <20250908000448.180088-3-balbirs@nvidia.com> From: David Hildenbrand 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250908000448.180088-3-balbirs@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: g7Nd6YQbTMivBs6-lXdZg3EwWK0PEW-1J_2BYqXqI_Q_1757592955 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.09.25 02:04, Balbir Singh wrote: > Extend core huge page management functions to handle device-private THP > entries. This enables proper handling of large device-private folios in > fundamental MM operations. > > The following functions have been updated: > > - copy_huge_pmd(): Handle device-private entries during fork/clone > - zap_huge_pmd(): Properly free device-private THP during munmap > - change_huge_pmd(): Support protection changes on device-private THP > - __pte_offset_map(): Add device-private entry awareness > > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Zi Yan > Cc: Joshua Hahn > Cc: Rakie Kim > Cc: Byungchul Park > Cc: Gregory Price > Cc: Ying Huang > Cc: Alistair Popple > Cc: Oscar Salvador > Cc: Lorenzo Stoakes > Cc: Baolin Wang > Cc: "Liam R. Howlett" > Cc: Nico Pache > Cc: Ryan Roberts > Cc: Dev Jain > Cc: Barry Song > Cc: Lyude Paul > Cc: Danilo Krummrich > Cc: David Airlie > Cc: Simona Vetter > Cc: Ralph Campbell > Cc: Mika Penttilä > Cc: Matthew Brost > Cc: Francois Dugast > > Signed-off-by: Matthew Brost > Signed-off-by: Balbir Singh > --- > include/linux/swapops.h | 27 +++++++++++++++++++ > mm/huge_memory.c | 60 ++++++++++++++++++++++++++++++++++++----- > mm/pgtable-generic.c | 6 +++++ > 3 files changed, 86 insertions(+), 7 deletions(-) > > diff --git a/include/linux/swapops.h b/include/linux/swapops.h > index 64ea151a7ae3..59c5889a4d54 100644 > --- a/include/linux/swapops.h > +++ b/include/linux/swapops.h > @@ -594,6 +594,33 @@ static inline int is_pmd_migration_entry(pmd_t pmd) > } > #endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ > > +#if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_ARCH_ENABLE_THP_MIGRATION) > + > +/** > + * is_pmd_device_private_entry() - Check if PMD contains a device private swap entry > + * @pmd: The PMD to check > + * > + * Returns true if the PMD contains a swap entry that represents a device private > + * page mapping. This is used for zone device private pages that have been > + * swapped out but still need special handling during various memory management > + * operations. > + * > + * Return: 1 if PMD contains device private entry, 0 otherwise > + */ > +static inline int is_pmd_device_private_entry(pmd_t pmd) > +{ > + return is_swap_pmd(pmd) && is_device_private_entry(pmd_to_swp_entry(pmd)); > +} > + > +#else /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */ > + > +static inline int is_pmd_device_private_entry(pmd_t pmd) > +{ > + return 0; > +} > + > +#endif /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */ > + > static inline int non_swap_entry(swp_entry_t entry) > { > return swp_type(entry) >= MAX_SWAPFILES; > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 26cedfcd7418..2af74e09b279 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1703,8 +1703,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > if (unlikely(is_swap_pmd(pmd))) { > swp_entry_t entry = pmd_to_swp_entry(pmd); > > - VM_BUG_ON(!is_pmd_migration_entry(pmd)); > - if (!is_readable_migration_entry(entry)) { > + VM_WARN_ON(!is_pmd_migration_entry(pmd) && > + !is_pmd_device_private_entry(pmd)); > + Wrong indentation. > + if (is_migration_entry(entry) && > + !is_readable_migration_entry(entry)) { Dito. Wonder if we want to be more explicit. if (is_readable_migration_entry(enrty) || is_readable_exclusive_migration_entry)) { > entry = make_readable_migration_entry( > swp_offset(entry)); > pmd = swp_entry_to_pmd(entry); > @@ -1713,7 +1716,37 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > if (pmd_swp_uffd_wp(*src_pmd)) > pmd = pmd_swp_mkuffd_wp(pmd); > set_pmd_at(src_mm, addr, src_pmd, pmd); > + } else if (is_device_private_entry(entry)) { > + /* > + * For device private entries, since there are no > + * read exclusive entries, writable = !readable > + */ > + if (is_writable_device_private_entry(entry)) { > + entry = make_readable_device_private_entry( > + swp_offset(entry)); Put this on a single line. > + pmd = swp_entry_to_pmd(entry); > + > + if (pmd_swp_soft_dirty(*src_pmd)) > + pmd = pmd_swp_mksoft_dirty(pmd); > + if (pmd_swp_uffd_wp(*src_pmd)) > + pmd = pmd_swp_mkuffd_wp(pmd); > + set_pmd_at(src_mm, addr, src_pmd, pmd); > + } > + > + src_folio = pfn_swap_entry_folio(entry); > + VM_WARN_ON(!folio_test_large(src_folio)); > + > + folio_get(src_folio); > + /* > + * folio_try_dup_anon_rmap_pmd does not fail for > + * device private entries. > + */ > + ret = folio_try_dup_anon_rmap_pmd(src_folio, > + &src_folio->page, > + dst_vma, src_vma); > + VM_WARN_ON(ret); Please just drop the ret + VM_WARN_ON here, like we did in the PTE case. > } > + > add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR); > mm_inc_nr_ptes(dst_mm); > pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable); > @@ -2211,15 +2244,17 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > folio_remove_rmap_pmd(folio, page, vma); > WARN_ON_ONCE(folio_mapcount(folio) < 0); > VM_BUG_ON_PAGE(!PageHead(page), page); > - } else if (thp_migration_supported()) { > + } else if (is_pmd_migration_entry(orig_pmd) || > + is_pmd_device_private_entry(orig_pmd)) { Indentation ... > swp_entry_t entry; > > - VM_BUG_ON(!is_pmd_migration_entry(orig_pmd)); > entry = pmd_to_swp_entry(orig_pmd); > folio = pfn_swap_entry_folio(entry); > flush_needed = 0; > - } else > - WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); > + > + if (!thp_migration_supported()) > + WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); > + } > > if (folio_test_anon(folio)) { > zap_deposited_table(tlb->mm, pmd); > @@ -2239,6 +2274,12 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > folio_mark_accessed(folio); > } > > + if (folio_is_device_private(folio)) { > + folio_remove_rmap_pmd(folio, &folio->page, vma); > + WARN_ON_ONCE(folio_mapcount(folio) < 0); > + folio_put(folio); > + } > + > spin_unlock(ptl); > if (flush_needed) > tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE); > @@ -2367,7 +2408,8 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > struct folio *folio = pfn_swap_entry_folio(entry); > pmd_t newpmd; > > - VM_BUG_ON(!is_pmd_migration_entry(*pmd)); > + VM_WARN_ON(!is_pmd_migration_entry(*pmd) && > + !folio_is_device_private(folio)); > if (is_writable_migration_entry(entry)) { > /* > * A protection check is difficult so > @@ -2380,6 +2422,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > newpmd = swp_entry_to_pmd(entry); > if (pmd_swp_soft_dirty(*pmd)) > newpmd = pmd_swp_mksoft_dirty(newpmd); > + } else if (is_writable_device_private_entry(entry)) { > + entry = make_readable_device_private_entry( > + swp_offset(entry)); > + newpmd = swp_entry_to_pmd(entry); > } else { > newpmd = *pmd; > } > diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c > index 567e2d084071..604e8206a2ec 100644 > --- a/mm/pgtable-generic.c > +++ b/mm/pgtable-generic.c > @@ -292,6 +292,12 @@ pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp) > *pmdvalp = pmdval; > if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval))) > goto nomap; > + if (is_swap_pmd(pmdval)) { > + swp_entry_t entry = pmd_to_swp_entry(pmdval); > + > + if (is_device_private_entry(entry)) > + goto nomap; > + } Couldn't we do here if (!pmd_present(pmdval)) goto nomap; To replace the original pmd_none() .. check. A page table must always be present IIRC. -- Cheers David / dhildenb