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 AF5803939C9; Tue, 22 Sep 2026 11:34:07 +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=1790076849; cv=none; b=RbQLP8M9B/9j7+punKXXIOi2MY+fwy1yxeOq5IGGZ/I/ocQw2eQ8eQkWa8E60PWQAKANNiQTuNg5s1eH8NEZ1FzrpHU1bqX20wb+5xPPU7A4C5Q97mJJFFyA4DP+XRXuthzt+U5rzg8cEXAGCyZ+Nf70/R33zHw+3dDLev1PjfQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790076849; c=relaxed/simple; bh=dmzfc6qmGUTIypccHIyMZjitJeRkUw593gO1VcnX6ks=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DBbfbTkeApIW08oE3XpeSHg2d3TsT8x+tr2yRQfOvjg6/O+r7lFWwbZgREjTNlfB8KxQCNK+IdSzdMfCLUtLhS10XkKpTg0+Bnzkr5MFthdzn76b/HHpCFmLvNHekhv61P/FNvHhJ6e7P5sZZGT/5mElw7/mX1ywF0m97DzMldg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=No/mihmV; 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="No/mihmV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C0D61F000FF; Tue, 22 Sep 2026 11:33:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790076847; bh=K0n7/b29134nS+A3GTeL665iC4ky8Dr2fCKiIHfp5lU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=No/mihmVNqVRgSiORpP9GZrDVA8StBXiN3ICK+I68z9IfS5uPNpmcyrkzIQoHi7Eb W2iHfOjGJwMnPTk579caztzDNPQ/jGV4CuahjjY5463D/f9fhKEqcQbMCN+MzjKIgP rgQh2QlpecS019H0w4achEtS/nZafcDoy5gI/c7rMkaolkLEN5zOfSqpAZJMAK94r9 HpMSYxAV9aowyRlAPS+S3uM4c9GxpLj/2HST9uuGP4M+0GOjNGpr1WNuzN/HJzPu61 2TldujEpeVrMQtmEH1LZ0FA3bu3HfzIZaN/JhcXBJKXDiZm+tmnrxTXjqZ4mqhLHwJ hacM3FJVAiYkA== Message-ID: Date: Tue, 22 Sep 2026 13:33:51 +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 9/21/26 16:31, Breno Leitao wrote: > On Fri, Sep 18, 2026 at 10:16:25PM +0200, David Hildenbrand (Arm) wrote: >> On 9/18/26 17:22, Breno Leitao wrote: >>> >>> Right, we have two source for poisoned page information, today. >>> >>> 1) LINUX_EFI_POISONED_MEMORY: Used to track memory block that got >>> poisioned, and will be passed around during kexec. >>> 2) PG_hwpoison on struct page: Used by the memory subsystem to avoid >>> touching it. >> >> How are both kept in sync? See below. > > The EFI table is only written when there is a memory failure. That is > the only thing that writes to it: > > action_result() -> efi_hwpoison_record_pfn() -> set_bit() > > You can see it on patch "mm/memory-failure: efi: record > hardware-poisoned frames into the poisoned-memory table" > > Then, when the kernel kexecs into a second kernel, the EFI config table > is queried and the pages are poisoned from it at boot, as they are > getting into the buddy allocator, in __free_pages_core(). I am not sure that is really the right place. That means we only poison free memory. Shouldn't we poison as soon as we initialize the memmap, and check whether any memblock allocations ended up on that poisoned memory and bail out? [...] > >>> You might ask why I do not just count the bits set in the bitmape and >>> multiply by the frames a unit covers. >>> >>> That was my first try. It over-counts: a bit stands for a whole 2M unit, >>> but only the frames that reach __free_pages_core() get flagged -- CMA >>> comes back through __free_pages(), the initrd and __init memory through >>> free_reserved_pages(), and KHO-preserved frames never get an initialised >>> struct page at all. >> >> Why are other hwpoisoned pages not flagged? If initrd or anything else is >> hwpoisoned, we should not be running this kernel? > > For the initrd and the image, the previous kernel's record cannot stop > this kernel's loader from placing them on a bad frame. If that happens > we consumed the poison in the relocation memcpy, long before any of this > code runs. That is the kexec segment placement problem, which Kiryl > raised on the RFC and which I split into its own series, which is landed > in some mm tree already. > > https://lore.kernel.org/all/20260812-kexec_posioned-v6-0-e477887086f0@debian.org/ > > >>> >>> And the over-count cannot be undone later. >> >> The inconsistency is worrisome. >> I wouldn't say that I hate it but it certainly has "great, more hwpoison hacks" >> smell to it. >> >> We have enough semi-broken hwpoison ... stuff ... in our code base already. So >> I'm hoping we're not adding more to it? >> >>> If the walk itself is what bothers you, the way out is not the bitmap >>> but counting as we flag: hwpoison_boot_page() already knows the pfn, so >>> it can bump a per-block-id counter in a small memblock array that >>> memblk_nr_poison_init() then just reads. >> >> The inconsistency is what worries me. >> >> And that we have pages we are told are hwpoisoned but we seem to ignore that and >> carry on with our kernel letting it boot? > > The walk exists precisely because of that inconsistency: the counter has > to match the frames that actually carry the flag, and the bitmap says > more than that. > > If we drop the page walk, then there is change for inconsistency, but, > as-is, there is no inconsistency. > > So, I am planning to keep the page walk above, when there is a poisoned > page in the memory block, avoiding any inconsitency. How about we keep it very simple and don't mix information from two different sources? That is, remove that bitmap scan here entirely. We should process the bitmap exactly once when initializing the memmap. >From that point on, the memmap should be our reliable source of information. For this code here, just remember globally whether we hwpoisoned any page. If so, just walk the memmap. If not (the 99.9999% of all systems, no need to scan anything). -- Cheers, David