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 F114A421888; Thu, 5 Feb 2026 15:48:18 +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=1770306499; cv=none; b=ian1ckskZk2J3A2oqsJxwUl1CsKcPX+fd+D33A/puuiKO5Fq97yDnbJNfQ9+JJxERVR2Yr/L6ytEx4+9hrCccLFljCxhJSzFs2/H3dv+Y/pT9lJiogT95zQN7rkhIrZ7UzF6rthVKAnur8jxQpLxFNIDqY5P0m1cmce3xavALCY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770306499; c=relaxed/simple; bh=VWhQr3Z+ccbJrrcfBGfZJZEc2/K4wBqICeXlpi3Prmk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mUNPWNVUlQquTeT3nlZC21n+8OEKdvTQ8gGe65sMPrPzZJPVXe5784O5JlE4hM6S0CCQihZOt5ntDxvQ6uO9qAzewZBH8NvoN2ytW+5KwuPNXvhcTme9S9MRvn4b75gobOcIyGx7wmk/jvVp70rwMlYTj4oTkMOzScNFfvca6lc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Nu876Qwq; 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="Nu876Qwq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64314C4CEF7; Thu, 5 Feb 2026 15:48:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770306498; bh=VWhQr3Z+ccbJrrcfBGfZJZEc2/K4wBqICeXlpi3Prmk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Nu876QwqbfV5qynC7ba1PNcW6kFoCiX0xZVJg94nQ/YAXjYFugrvsueR+JSpe2pae rY0c8JfG9b0JRDqQq4Bdt0GAAGY6BNk/zv8c38yUpeHoXwsdifhSzLinBTFN/V0Els iAKyKePSbqtE23p09QbWhgQhBbyVWbWFndo0F6gE0hqw0b/yi2PG6oWYQANy/Omti8 Nc0WwV5+q3NLPGWequp2spO0xxgan0o8bnhbcE4g7FWk60WSOiF76gkPRjnfrnLnF7 gYvEmGzE0oL1EF3oVxlAqGw1ynwGrzRJyw+5WNAEZBIGvWd8dEWsgXgor76Ac9oGz/ z/Q372FU9uAnA== Message-ID: Date: Thu, 5 Feb 2026 16:48:13 +0100 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 v4 1/2] mm/memory_hotplug: Add support to accept memory during hot-add To: Kiryl Shutsemau , "Pratik R. Sampat" Cc: linux-mm@kvack.org, linux-coco@lists.linux.dev, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, ardb@kernel.org, akpm@linux-foundation.org, osalvador@suse.de, thomas.lendacky@amd.com, michael.roth@amd.com References: <20260203174946.1198053-1-prsampat@amd.com> <20260203174946.1198053-2-prsampat@amd.com> <70be936e-e49d-4485-8d1e-416fdf8f40a4@amd.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/5/26 11:48, Kiryl Shutsemau wrote: > On Wed, Feb 04, 2026 at 09:50:09PM -0600, Pratik R. Sampat wrote: >> >> >> On 2/4/26 2:00 PM, David Hildenbrand (arm) wrote: >>> >>> I really hate that accepting (and un-accepting) hotplugged memory is different to accepting ordinary boot memory. >>> >>> Is there really no way we can get a reasonable implementation where we just call a generic accept_memory() and it will know what to do? >>> >> >> Sure, that shouldn't be impossible. >> >> The only reason I initially kept them separate is because we accept and update >> the bitmap unconditionally. This mainly applies to cold-plugged memory since >> their bitmap state after remove shouldn't matter. However, as we are now >> correctly setting the bits in the hot-remove path we should be fine accepting >> from the for_each_set_bitrange_from() logic within accept_memory(), I think. >> >> Something like so? >> >> diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c >> index d11e7836200a..e56adfd382f8 100644 >> --- a/drivers/firmware/efi/unaccepted_memory.c >> +++ b/drivers/firmware/efi/unaccepted_memory.c >> @@ -36,6 +36,7 @@ void accept_memory(phys_addr_t start, unsigned long size) >> unsigned long range_start, range_end; >> struct accept_range range, *entry; >> phys_addr_t end = start + size; >> + phys_addr_t bitmap_end; >> unsigned long flags; >> u64 unit_size; >> >> @@ -44,6 +45,21 @@ void accept_memory(phys_addr_t start, unsigned long size) >> return; >> >> unit_size = unaccepted->unit_size; >> + bitmap_end = unaccepted->phys_base + unaccepted->size * unit_size * BITS_PER_BYTE; >> + >> + /* Memory completely beyond bitmap: hotplug memory, accept unconditionally */ >> + if (start >= bitmap_end) { >> + arch_accept_memory(start, end); >> + return; >> + } >> + >> + /* Memory partially beyond bitmap */ >> + if (end > bitmap_end) { >> + arch_accept_memory(bitmap_end, end); >> + end = bitmap_end; >> + } > > You are calling arch_accept_memory() on every memory allocation if the > memory is not represented in the bitmap. Hard NAK. In which scenarios would we not have memory represented in the bitmap? Guests with <4 GiB? (how does kexec work?) Anything else? -- Cheers, David