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b=YQZwVmSXvyJGDGxoiIKuILLAsmdM03f+GMfUozW8IVPM7vAEbHpx8A2UTwTex3jHf DifV3qiO4PBwahZum1RTZFZGYdnV1lJwKpDYrawDZ6vHn233grx/DJDDdsbQLnMF99 GgIYJrm1CE/B7BdcJrccaQ16wJIF22i/Nf5MUKCFpuRkGTPwPZUJRAXdj4fbkYF+Vs UBEGjHU6DnDn14B6ltXxuUfyosVkJpwNhOJPi12iwasHixlxEqvlEI6AQ4YnpsUJxt t1ZVlKu0aPEMvUqour9cd3YjV1lNaKfadqLD48IqwghpXrEVWwtEjw6yGEUdfHK8Xv Me9TNxuE23Shg== Message-ID: <15977036-c5a4-477f-8cef-3bfd0a585c55@kernel.org> Date: Thu, 17 Sep 2026 17:38:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/huge_memory: disallow raw PMD mappings of the huge zero page To: Lance Yang , akpm@linux-foundation.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260917121010.60966-1-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20260917121010.60966-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 1601120008 X-Stat-Signature: chncpssps6zrx6s4icmd4um5699fhs9h X-Rspamd-Server: rspam01 X-HE-Tag: 1789659527-501579 X-HE-Meta: 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 Lr5Qezta zP2cNBJRhcpRUnCbiUnXNfixq1yhfCLCqiKVpq0XNxy3kEmU24v9et0aSuxE/iVkEd1MlPlHPfIWw92Zxe31Uw/+mTuMqVbhA0Ds4NsMN6vs6WWOZgWXFqR7AlNeAyxLOJwLPcKEBy7u9wvTTbTNt0FZ8iw+Qfuf7DEgmS4s+YM8U6zjlkVczwATJ0z7K9jYmHh2+Afxp2QpqITAe9Yw8/YcvcsE7F17zTsG5rSUQqcgYCKM1OTqOPlSnjvLXsXJ1Ou0RoIXoTzRm2yTEp5TbzTNh91kIZP3wd5CTuDOtmJCq5J+H0pteGmGephYSPDlPMfRT+evmY+jOw/k= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/17/26 14:10, Lance Yang wrote: > vm_mixed_zeropage_allowed() validates zeropage insertion into > VM_MIXEDMAP VMAs. No in-tree user needs to insert the huge zero page > through vmf_insert_pfn_pmd(). I think we want a clear description why we would want to forbid it. Is it related to vm_mixed_ok/vm_mixed_zeropage_allowed? Once again I am confused about which interfaces are actually valid for VM_MIXEDMAP.> > Return VM_FAULT_SIGBUS if vmf_insert_pfn_pmd() is asked to map it. > > Link: https://lore.kernel.org/linux-mm/f76beaf8-351a-4b22-b362-a945a5e1af6a@kernel.org/ > Suggested-by: Kiryl Shutsemau > Suggested-by: David Hildenbrand > Signed-off-by: Lance Yang > --- > mm/huge_memory.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index bfd972b997f9..c02f21ce4f4c 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1728,6 +1728,9 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, unsigned long pfn, > (VM_PFNMAP|VM_MIXEDMAP)); > BUG_ON((vma->vm_flags & VM_PFNMAP) && vma_is_cow_mapping(vma)); > > + if (unlikely(is_huge_zero_pfn(pfn))) > + return VM_FAULT_SIGBUS; > + > pfnmap_setup_cachemode_pfn(pfn, &pgprot); > > return insert_pmd(vma, addr, vmf->pmd, fop, pgprot, write); -- Cheers, David