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 F183B3D667D; Thu, 10 Sep 2026 10:05:33 +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=1789034743; cv=none; b=H01EL34jnHAu9GAYL70WcKc1BQmvhjOi3PrR9hcJr+TEB7Y0/lK5HyWQhmmmJuHm2Sbn40Ugp4+S3YUNAMJbfbpdqJM5iV2fsLK/K/h3v5IICKM/Qz2UMRCy/e9HUYNsb6jdeeghdC/dkIQZKtOBGa6YN87qRYThOi/2sxqdO8A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789034743; c=relaxed/simple; bh=3z0WN4zi1UJFms75zdwhQXh4Qlgba5XU53bM7EcRgQc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=REgr2EKzHmDrVQ78r0ArI/VNnJ49rwMYyyl45ol6WNh+PJwQefvkK5A4eNY+tuVrOFVGyOJTUyiP1Nda4oPb9o+TYnoqxTVJqonn1a0hmY/QzWb7HZHmlW7SQtI16J4krtTUO91QMyZH28zUfsV9k9zUH5yBBsa957fgjpcIhUo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QzBHpLL7; 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="QzBHpLL7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30A3C1F000FF; Thu, 10 Sep 2026 10:05:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789034729; bh=foN56LOD6/Sr9Fuua4UGrrARCTUwXc66j3xzHR63FGE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=QzBHpLL73o0QRHBq1BtDWHfKhjgH7vYQlOQTmd/7CsBCnteHkCGmQ//nhe1xBe+XC B+J/EOTATm18+r68ByFk08E1DHO/jGR+rAnUx1rseFVGhpIozwzwFhzDF7sOLJLeQ+ I9XUGlHlf+t7B+P5tn0YTppgcLchcfIELLFXodhjEkX4ufh+VLtkzkBdboHmg+39OE 6g/BYc6mcelHh8Dvj1YRbZL2cncQvh7KDpBKn2qNLUqTx/qsd0Ozx7Dp6POJfFAdiR tfvp/PiJB/ZsLE17ZTAn6ACIgPYGEels8eKnoLC09LSAs9Q4EgK8NWvE4szHuqmUUQ HqOFKQ1qoF9QQ== Message-ID: Date: Thu, 10 Sep 2026 12:05:15 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/9] KVM: guest_memfd: implement folio migration for non-confidential VMs To: Shivank Garg , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Paolo Bonzini , Shuah Khan , Chao Peng , Nikunj A Dadhania , Michael Roth , Pankaj Gupta , Ackerley Tng , Sean Christopherson , Vishal Annapurve , Nikita Kalyazin , Patrick Roy , Pratik Sampat , Ashish Kalra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Jonathan Corbet , Shuah Khan , Peter Shier , Jim Mattson , Ricardo Koller , Ira Weiny , Fuad Tabba Cc: linux-fsdevel@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org References: <20260805-shivank-gmem-migrate-v3-0-00d8bdec4e1d@amd.com> <20260805-shivank-gmem-migrate-v3-3-00d8bdec4e1d@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: <20260805-shivank-gmem-migrate-v3-3-00d8bdec4e1d@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/5/26 08:40, Shivank Garg wrote: > Implement kvm_gmem_migrate_folio() using filemap_migrate_folio() for > non-confidential VMs but don't enable it yet. guest_memfd mappings > are still marked unmovable, so MM never calls it. > > MM invokes ->migrate_folio() callback with folios already locked and > acquires the invalidate lock afterwards. kvm_gmem_punch_hole() takes > the invalidate lock before locking folios during truncation, so > taking invalidate lock in migration callback can cause an ABBA-deadlock > situation. Use filemap_invalidate_trylock_shared() to avoid this. > > A subsequent patch adds an opt-in flag to change the mapping to > movable and enable migration. Non-confidential VMs can use > host-side copy via folio_mc_copy(), whereas confidential VMs will > require firmware-assisted copying before they can opt in. > > Signed-off-by: Shivank Garg > --- > virt/kvm/guest_memfd.c | 36 ++++++++++++++++++++++++++++++++++-- > 1 file changed, 34 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 169f75f95433..583341d593c9 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -488,13 +488,45 @@ static struct file_operations kvm_gmem_fops = { > .fallocate = kvm_gmem_fallocate, > }; > > +#ifdef CONFIG_MIGRATION > static int kvm_gmem_migrate_folio(struct address_space *mapping, > struct folio *dst, struct folio *src, > enum migrate_mode mode) > { > - WARN_ON_ONCE(1); > - return -EINVAL; > + struct inode *inode = mapping->host; > + pgoff_t start, end; > + int ret; > + > + /* > + * Migration invokes ->migrate_folio() while holding the folio lock. > + * Use a non-blocking trylock to avoid inverting the lock order with > + * truncation, which takes the invalidate lock before locking the > + * folios. > + */ > + if (!filemap_invalidate_trylock_shared(mapping)) > + return -EAGAIN; > + > + start = src->index; > + end = start + folio_nr_pages(src); > + > + kvm_gmem_invalidate_start(inode, start, end); > + > + /* > + * For non-confidential guests the folio is host-readable, so > + * filemap_migrate_folio() can copy the contents itself via > + * folio_mc_copy(). > + * For confidential guests, this would need firmware assistance. > + */ I think this is all more closely related to mapping_inaccessible(). If accessible, this is just trivially true that we can support this. So I would not comment on what to do for confidential VMs for now, and limit it only to the shared-only case where pages are accessible. -- Cheers, David