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 EB73B4E50AF; Fri, 18 Sep 2026 12:18:19 +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=1789733902; cv=none; b=qzCKUTmmSl/d7f+GKZH5vNTcKw3yxH78F+06oL0etkzfrMII27wijV5I2Q0mB9ozN9IZG6p/KBaYzV0o+ClzkvL4O44LRhJoVa1JB3P/jx6Mh6ZYG4EO+mk71C1/aTnjWhrz0XKOP/shvnHDIhuPQ3hedjktmZ+87Q3u2q2I1Ec= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789733902; c=relaxed/simple; bh=EZhZBs6JvnZvXfuZrIsPlcAv0CRX2geRYv1T0qsDlBk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rizhlxJ12JRhHdmDRlL0EliRBoh00Azm3dpIe5BzXkTVNwhpF8kKZO6RBdJ+dKd9v5ExY44RQv2A7pLcQkPrmcRaony1dPJ9YFTwNbpmndQeCoA6YdNxk9Eu3BNlzHM4MAWvF7naEsrfr+hDmduVtAV1v4ZQGAiMELam5EMJBpg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nHi3LIql; 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="nHi3LIql" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 251121F000FF; Fri, 18 Sep 2026 12:18:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789733899; bh=iraf2G8GnLk55v/tOz9PuW5FKw3tZzsJG7inOso05Qw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nHi3LIqlfCjI2cn+NwQvM+CZ6Xylz1qzVBvMVHU9ino6iJj0S1Gv6y6qT3JyuiqVw 9NwLROYnHXnhBnwRDXtkpuBo0RiuhYfP372H/PrZ5Nmt5H7qMGr4ZvjDP7Dwj0hTX6 t9ukArpPNzDq/p+rmRjeDwz2aikNKZW1dqPzMlSgMIrL0+8GchhWkMtqhxcMBbwlYM HZJToJz+7PH7D09H/haTWnVS9i0c84gZW++nFFnRWSopuUlryKmKqMgcjwZv21FwQz Y2Neq90H9WGRd9haugFuPUNOpXZWqNTYrEEcEwM034L57yQl4mqvl9boN1WzzbFTxb aVrL4ESb4oOWg== Message-ID: Date: Fri, 18 Sep 2026 14:18:03 +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 v5 7/9] drivers/base/memory: count inherited poisoned frames into the block To: Breno Leitao Cc: Ard Biesheuvel , Ilias Apalodimas , Miaohe Lin , Naoya Horiguchi , Andrew Morton , kas@kernel.org, kexec@lists.infradead.org, Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Brendan Jackman , Johannes Weiner , Zi Yan , Oscar Salvador , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , hannes@cmpxchg.or, shakeel.butt@linux.dev, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, rmikey@meta.com, riel@surriel.com, harry@kernel.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, kernel-team@meta.com References: <20260915-hwpoison-kho-v5-0-3bc7a57bd503@debian.org> <20260915-hwpoison-kho-v5-7-3bc7a57bd503@debian.org> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/17/26 15:01, Breno Leitao wrote: > On Wed, Sep 16, 2026 at 04:51:40PM +0200, David Hildenbrand (Arm) wrote: >> On 9/16/26 11:35, Breno Leitao wrote: >>> >>> hmmm, I am not sure I see it that way. >>> >>> The loop only runs for a block the bitmap marks. On a machine with nothing >>> recorded the bitmap is all zeros, the range_contains_poisoned_memory() check >>> right above it returns false, and the loop never executes. >>> >>> What every boot does pay is that check, once per block. The stub installs >>> the table whether or not anything was ever recorded in it, so this is not a >>> NULL test: it is two 64-bit divisions by the unit size plus a >>> find_next_bit() over the single word a 128M block covers at one bit per 2M. >>> >>> The real cost (that "for loop above"), comes when you kexec (not on cold >>> boot -- given the bitmap is empty), and you are trying to init >>> a memory block that has poisoned pages into it. Which seems the right >>> trade-off, no? >>> >>> That said, can we do better? Yes. The silly win is to let the table say >>> whether anything was ever recorded in it, something like a >>> linux_efi_poisoned_memory->empty that the first recorded frame clears, >>> and return on that before the bitmap is reached at all. >>> >>> Is this what you are looking for, or something more drastic? >> >> Ah, that magical "range_contains_poisoned_memory" does a bitmap scan? >> >> I'm sorry, but that is absolutely confusing. >> >> There is no way someone will figure out that range_contains_poisoned_memory() >> queries some efi specific bitmap that won't even be able to represent any memory >> outside of it's range. >> >> I don't really have time to give a better solution, but starting with the >> naming, range_contains_poisoned_memory() is just absolutely misleading. > > Fair point, I'll clean up the naming in the next revision. > > I'll also add that ->empty field, which should help locate this bit > faster and may let us skip the bitmap query entirely on the happy path. > > Anything else you'd like addressed? > > Good to know this moved the needle from "David hates this feature" to > "David only hates the naming" -- I'll take that as progress. :-P ;) I think the crucial part is to find a way to cleanly distinguish our source of information, and also how the source does only apply to some memory. Regarding this patch here, I'd assume it's sufficient. But I do wonder why we are walking pages when we have a bitmap to walk/process at hand? -- Cheers, David