From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8B64C2D3225 for ; Tue, 14 Apr 2026 18:15:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776190540; cv=none; b=j2a9xnHNA+LGmE+GpDa10u+QebdgKneZWAgkrP0X9ntpInnkoyV1BYvB5fzOv254L1GWw7tz/6RxkYQxQ9Xx046J55IlfxA74WxNzAvtWvid5u4iWD3FY+tA9zKC26Di9mxoP6KpCwD+8cHt9+FmrN2NHJFlcYFO4rm45eurLDo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776190540; c=relaxed/simple; bh=q0rUomqXSUV8ZGyZgbkZbpYJ8u2tAB/veX/90Uauzv4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eZj5ERFoqU9v424tZI0CjUNydG6lA4wlOI8zkbZl3xDPFxs//VNrlI49ijsiCrfDew7rmfAYmP2uJlm826PVAds8T3FLl6TLa5qyWCNgS5yQNjIYjOyDCM4Nw8DS/BWHHxVRItJj466tKiWDhY/jCGd3NkFEqfh2U7OCIgTmDHg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=En1bHn1r; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="En1bHn1r" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D010CC2BCB4; Tue, 14 Apr 2026 18:15:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776190540; bh=q0rUomqXSUV8ZGyZgbkZbpYJ8u2tAB/veX/90Uauzv4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=En1bHn1ry5NBVqC358619JwGCQlH+ElgApcKZ08XaIllICM/Byuv6aF8RKyb4kBGM B1osRyNHagiELNjD3Us7OZjscR/L7cbrV7dVFJOZfu3ZkROpt3JLPxIjoSZACH298L 9u3ZdkTG+FCLKQYji01Sulz+2WgAHZHHvtbRAk5HFfEaRvyRNkIvawoy5KFgsL8Dh+ pT7b46v4MS8KNyiNIkM6rr12UK5Kc95QI49HeaGYHtwY7rVs0mYaFjcHpIFE9XLpPF AAKVSO+6GdItulWWlD+cbLnHJXRSZ40CBYnNIFYqPX5QzQOf5hqtbAMpm7K2AoTkiK 2g/5N+V8MGtFA== Message-ID: <6417587a-7e43-4615-9e2c-50a245842f59@kernel.org> Date: Tue, 14 Apr 2026 20:15:31 +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 13/13] mm/huge_memory: add and use has_deposited_pgtable() To: Yin Tirui , Lorenzo Stoakes Cc: Andrew Morton , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <41b1ff54-c120-42ae-8b74-54767abf3554@gmail.com> <2f29f66b-46db-4925-b922-4add61b633bf@gmail.com> <53d748d3-4150-4e7b-8c1f-4c58587e9183@kernel.org> <6125defb-3aa4-494c-abed-982be684f839@gmail.com> 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: <6125defb-3aa4-494c-abed-982be684f839@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/14/26 17:14, Yin Tirui wrote: > On 4/14/26 17:44, David Hildenbrand (Arm) wrote: >> >> I mean, we need some indication to know also during folio splitting >> whether we can just discard the PMD, as we can refault it later, or >> whether we really have to install a PTE table. >> >> What if someone used remap_pfn_range() on some part of the VMA, and >> faults on another part? >> >> Doesn't really work. >> >> Do we have users of remap_pfn_range() that have ->fault set? If not, we >> should probably just disallow this combination. > > I did a quick tree-wide grep: > $ git grep -l "remap_pfn_range" | xargs grep -l "\.fault\s*=" > arch/powerpc/platforms/book3s/vas-api.c > drivers/infiniband/hw/hfi1/file_ops.c > drivers/uio/uio.c > drivers/vfio/pci/vfio_pci_core.c > fs/proc/vmcore.c > security/selinux/selinuxfs.c > > It turns out there are two users of this "hybrid" approach in the kernel: > 1. fs/proc/vmcore.c: It pre-maps via remap_pfn_range() but registers > mmap_vmcore_fault(). > 2. arch/powerpc/platforms/book3s/vas-api.c: It pre-maps via > remap_pfn_range(), but registers vas_mmap_fault(). > >> >> Then we know for sure whether something was installed through >> remap_pfn_range() or through a fault handler. >> > > How would you suggest we proceed here? How about we populate PMDs in remap_pfn_range() only if !fault? Then, if we have !fault, we know that the PMD is from remap_pfn_range() and has a disposed page table. Would that work? -- Cheers, David