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imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="sAMSqI/u"; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773066156; a=rsa-sha256; cv=none; b=kiN6SnzE8svW3jLzjBwlTLusJ89Run8ZACGWwA0+o09lHpBUzeT7zLHPFx0eFv/LdJvwCs 4hGayYbxATSnRXfIutdhwyiAXqNaOeBysCgVI32cRlVOP5OgvqcdQhwauRQwvnwJFtF6SL R8++KkBqiTJhccdMJwimIVJnBSCGsrQ= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 5C889600AE; Mon, 9 Mar 2026 14:22:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F3FEC4CEF7; Mon, 9 Mar 2026 14:22:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773066155; bh=5KlEfbz0Ee4iB8X6UNcKHVf2pxVqxGqjkSUK1qr0Ki4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=sAMSqI/uCvaejl/SUMKvoSWH6sSKm5gIS5a7zZC1gBP+slwLpC/zYJd9K6T2Li00b my7gQs9YzFHCkFHNeSo4WXKTjIdOzztCtEcIdwryUoOJpR7udIQN51pFPDwQhDlqU8 AVYjfJ3X63dHXNKTHVNtoG650ZchzyUZ2+f0pcaTVbptv7OVZNYoyZ4/K5pR17HnMT JBF/S4MvLr9HbP1i+lUbJ88WOiEauPQLtObsYtQ6Tg5brdOIp+TGxXI3/IxRb6Nyt9 iaOghqdSWK+HOdfh9/ca+HrpHCnyXv1o6C3Ba+0qDpwi/Qs42oZby+pXqkp4bcrRuN pqPISn1qnChiQ== Message-ID: Date: Mon, 9 Mar 2026 15:22:28 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] binfmt_elf: Align eligible read-only PT_LOAD segments to PMD_SIZE for THP To: WANG Rui , Alexander Viro , Christian Brauner , Jan Kara , Kees Cook , Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260304114727.384416-1-r@hev.cc> 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: <20260304114727.384416-1-r@hev.cc> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 118F540012 X-Rspamd-Server: rspam07 X-Stat-Signature: w68s46nmir5xg3oeksiwept9qmicig1z X-Rspam-User: X-HE-Tag: 1773066155-401805 X-HE-Meta: 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 xUeAbkU5 +k+mWKXlNYsDaMekRvoMMDbjEvag74zZaMZW6UEBd+5XSkXZl07d+flMgDmNaiLsnuN2tkqGgr2LVSxUohh69cdL+EkmGsQCErE0wOhmZn2KnVMfvhZT/lJnZHnOvTBE7STCnTTcqkcglyOxC4GE7e9qF3vtXkuA+PIMGQIs9nWkUXxDRFLlbQ5k/eMj2zrVF5dnx53L3A44EBCUxKehzrtE07GwZFC1TGt+3TCwyI70MBKqw2KbP3n601zbjqMaTQ9+GeqCQ3j4izwpBfAfH6A1msSBqfk0zHfi8L6+0ifZDSGihM3fhuuMONYXJbnVcjN9A Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/4/26 12:47, WANG Rui wrote: > When Transparent Huge Pages (THP) are enabled in "always" mode, > file-backed read-only mappings can be backed by PMD-sized huge pages > if they meet the alignment and size requirements. > > For ELF executables loaded by the kernel ELF binary loader, PT_LOAD > segments are normally aligned according to p_align, which is often > only page-sized. As a result, large read-only segments that are > otherwise eligible may fail to be mapped using PMD-sized THP. > > A segment is considered eligible if: > > * THP is in "always" mode, > * it is not writable, > * both p_vaddr and p_offset are PMD-aligned, > * its file size is at least PMD_SIZE, and > * its existing p_align is smaller than PMD_SIZE. > > To avoid excessive address space padding on systems with very large > PMD_SIZE values, this optimization is applied only when PMD_SIZE <= 32MB, > since requiring larger alignments would be unreasonable, especially on > 32-bit systems with a much more limited virtual address space. > > This increases the likelihood that large text segments of ELF > executables are backed by PMD-sized THP, reducing TLB pressure and > improving performance for large binaries. > > This only affects ELF executables loaded directly by the kernel > binary loader. Shared libraries loaded by user space (e.g. via the > dynamic linker) are not affected. > > Signed-off-by: WANG Rui > --- > Changes since [v1]: > * Dropped the Kconfig option CONFIG_ELF_RO_LOAD_THP_ALIGNMENT. > * Moved the alignment logic into a helper align_to_pmd() for clarity. > * Improved the comment explaining why we skip the optimization > when PMD_SIZE > 32MB. > > [v1]: https://lore.kernel.org/linux-fsdevel/20260302155046.286650-1-r@hev.cc > --- > fs/binfmt_elf.c | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index fb857faaf0d6..39bad27d8490 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -28,6 +28,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -489,6 +490,30 @@ static int elf_read(struct file *file, void *buf, size_t len, loff_t pos) > return 0; > } > > +static inline bool align_to_pmd(const struct elf_phdr *cmd) > +{ > + /* > + * Avoid excessive virtual address space padding when PMD_SIZE is very > + * large (e.g. some 64K base-page configurations). > + */ > + if (PMD_SIZE > SZ_32M) > + return false; > + > + if (!hugepage_global_always()) > + return false; > + > + if (!IS_ALIGNED(cmd->p_vaddr | cmd->p_offset, PMD_SIZE)) > + return false; > + > + if (cmd->p_filesz < PMD_SIZE) > + return false; > + > + if (cmd->p_flags & PF_W) > + return false; > + > + return true; > +} > + > static unsigned long maximum_alignment(struct elf_phdr *cmds, int nr) > { > unsigned long alignment = 0; > @@ -501,6 +526,10 @@ static unsigned long maximum_alignment(struct elf_phdr *cmds, int nr) > /* skip non-power of two alignments as invalid */ > if (!is_power_of_2(p_align)) > continue; > + > + if (align_to_pmd(&cmds[i]) && p_align < PMD_SIZE) > + p_align = PMD_SIZE; The function name does not make any sense when reading this chunk. "should_align_XXX_to_pmd" ? -- Cheers, David