From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0F8912C21FD; Fri, 18 Sep 2026 20:00:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789761642; cv=none; b=hG1p/uCZoRpiiLaQfkH45oyqHVwVU5+lLUcU3q0BA3UYcfJkRUjaAClWy5+S7bmsCNtnYvDr4ZPCBBhATfPVPPHI6F3o2rzAJAdmxjpilZs3hY07pIavMgBrGCz5y1W9Cdnc47Yk20sDfk9vgYDtMP1it9Xb9S/EF+gzz8BCYLk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789761642; c=relaxed/simple; bh=QXNmyJLdm7eVhgJDNvEPLzg73ji34JU1iopw6Z+dg4M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=flICNqOEjeueVb+gFYgSIGjzwccq4yAOqdLN3Umys7o8Gdz2f/q6pU5LFw22PA+plqEJEKuQmQ1ZhAh8BXYCDv7CdDAKFjPm1q+ng2wvQudwrL7k6JbmHooInAGnjel1gcWCCOn7gwlznaFsBWEQC5mNtvJ2qQ16Q1PJMD7CY40= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jXwXVqX4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jXwXVqX4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 559CB1F000FF; Fri, 18 Sep 2026 20:00:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789761640; bh=DqRuy6t8l0KMBsc8eMIIlqtXIJciSthuiHWYk9gxWWQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jXwXVqX45pm1S5/YzhSxREbtC4KN6fHavNEtSUadv2NX6CDWi/5GQG5+EXoS7kNZL z96gMCf/3OX5NhSzsj/QiOO1t3h++itVSy1RLabKNoyv/ZtCjcRWT2VZI4qBrQAS59 fIlbYqQnB0l/sDHT8n+jyftddKfjdRLarGpeYbecixZgXsqu+5Dfjwztm+s+Bf6KC1 0KxRZ3DNN8CrfEcasmcNn8MsT0c0IdeinzkdY3X6QejS2OF1o4Ay3Uo7sTNxu6i3fk 7rKhEw91gcHRrTbi0P6RtIWFjs77qURfBKonQtTPvEi2UumT9+aAFJ4AgOZUjxACRc UGT9wFAH4fr8A== Message-ID: <1d1e38d8-cc1a-4a53-80c7-c0ef75a70105@kernel.org> Date: Fri, 18 Sep 2026 22:00:31 +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 4/6] arm64: use hw_pte_t for fixmap HW PTEs To: Ryan Roberts , Muhammad Usama Anjum , Catalin Marinas , Will Deacon , Mark Rutland , Ard Biesheuvel , Ilias Apalodimas , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org References: <20260914-pte0_arm-v1-0-bb53b663e396@arm.com> <20260914-pte0_arm-v1-4-bb53b663e396@arm.com> <829523cd-85a4-4f8e-b9f2-f3c1d7ce4fb1@arm.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: <829523cd-85a4-4f8e-b9f2-f3c1d7ce4fb1@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/18/26 18:03, Ryan Roberts wrote: > On 14/09/2026 14:51, Muhammad Usama Anjum wrote: >> fixmap_pte() returns a pointer into bm_pte, and early_fixmap_init_pte() >> installs those arrays as page tables. Their elements are therefore >> HW PTEs. >> >> Change the element type of bm_pte to hw_pte_t so it matches the HW PTE >> pointers returned and passed to the accessors. This is needed before >> ARCH_HAS_HW_PTE_T makes HW PTEs and SW PTE values distinct types; the >> array dimensions and placement are unchanged. >> >> Signed-off-by: Muhammad Usama Anjum >> --- >> arch/arm64/mm/fixmap.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c >> index 237a9136bc73b..709a97fe327d8 100644 >> --- a/arch/arm64/mm/fixmap.c >> +++ b/arch/arm64/mm/fixmap.c >> @@ -31,7 +31,7 @@ static_assert(NR_BM_PMD_TABLES == 1); >> >> #define BM_PTE_TABLE_IDX(addr) __BM_TABLE_IDX(addr, PMD_SHIFT) >> >> -static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __bss_pgtbl; >> +static hw_pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __bss_pgtbl; > > I think in my original proposal it was impossible to have a hw_pte value; only a > hw_pte pointer was possible. Being able to create hw_pte values means that it is > possible that a hw_pte_t pointer is not actually pointing to an entry in a HW > pgtable. The main motivation for this is that we want to dereference neighbours > of a hw pte based on it's pointer and be confident that it is safe. I think this > removes some of the safety. If you follow some of the related discussions on the core-mm series, there is a path forward to go further into that direction. People instantiating a hw_pte_t on the stack are not really a concern right now. -- Cheers, David