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(p200300d82f22060053c7df437dc3ae39.dip0.t-ipconnect.de. [2003:d8:2f22:600:53c7:df43:7dc3:ae39]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45a2231f7e8sm127205855e9.14.2025.08.18.00.48.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Aug 2025 00:48:56 -0700 (PDT) Message-ID: <0e613cf3-7ff1-49d9-9fff-fcf824f2df72@redhat.com> Date: Mon, 18 Aug 2025 09:48:54 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V5 mm-hotfixes 2/3] mm: introduce and use {pgd,p4d}_populate_kernel() To: Harry Yoo , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andy Lutomirski , Peter Zijlstra , "H . Peter Anvin" Cc: Andrey Ryabinin , Arnd Bergmann , Dennis Zhou , Tejun Heo , Christoph Lameter , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Juergen Gross , Kevin Brodsky , Oscar Salvador , Joao Martins , Lorenzo Sccakes , Jane Chu , Alistair Popple , Mike Rapoport , Gwan-gyeong Mun , "Aneesh Kumar K . V" , Uladzislau Rezki , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Qi Zheng , Ard Biesheuvel , Thomas Huth , John Hubbard , Ryan Roberts , Peter Xu , Dev Jain , Bibo Mao , Anshuman Khandual , Joerg Roedel , x86@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Kiryl Shutsemau References: <20250818020206.4517-1-harry.yoo@oracle.com> <20250818020206.4517-3-harry.yoo@oracle.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 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: <20250818020206.4517-3-harry.yoo@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18.08.25 04:02, Harry Yoo wrote: > Introduce and use {pgd,p4d}_populate_kernel() in core MM code when > populating PGD and P4D entries for the kernel address space. > These helpers ensure proper synchronization of page tables when > updating the kernel portion of top-level page tables. > > Until now, the kernel has relied on each architecture to handle > synchronization of top-level page tables in an ad-hoc manner. > For example, see commit 9b861528a801 ("x86-64, mem: Update all PGDs for > direct mapping and vmemmap mapping changes"). > > However, this approach has proven fragile for following reasons: > > 1) It is easy to forget to perform the necessary page table > synchronization when introducing new changes. > For instance, commit 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory > savings for compound devmaps") overlooked the need to synchronize > page tables for the vmemmap area. > > 2) It is also easy to overlook that the vmemmap and direct mapping areas > must not be accessed before explicit page table synchronization. > For example, commit 8d400913c231 ("x86/vmemmap: handle unpopulated > sub-pmd ranges")) caused crashes by accessing the vmemmap area > before calling sync_global_pgds(). > > To address this, as suggested by Dave Hansen, introduce _kernel() variants > of the page table population helpers, which invoke architecture-specific > hooks to properly synchronize page tables. These are introduced in a new > header file, include/linux/pgalloc.h, so they can be called from common code. > > They reuse existing infrastructure for vmalloc and ioremap. > Synchronization requirements are determined by ARCH_PAGE_TABLE_SYNC_MASK, > and the actual synchronization is performed by arch_sync_kernel_mappings(). > > This change currently targets only x86_64, so only PGD and P4D level > helpers are introduced. Currently, these helpers are no-ops since no > architecture sets PGTBL_{PGD,P4D}_MODIFIED in ARCH_PAGE_TABLE_SYNC_MASK. > > In theory, PUD and PMD level helpers can be added later if needed by > other architectures. For now, 32-bit architectures (x86-32 and arm) only > handle PGTBL_PMD_MODIFIED, so p*d_populate_kernel() will never affect > them unless we introduce a PMD level helper. > > Cc: > Fixes: 8d400913c231 ("x86/vmemmap: handle unpopulated sub-pmd ranges") > Suggested-by: Dave Hansen > Acked-by: Kiryl Shutsemau > Reviewed-by: Mike Rapoport (Microsoft) > Reviewed-by: Lorenzo Stoakes > Signed-off-by: Harry Yoo > --- Acked-by: David Hildenbrand -- Cheers David / dhildenb