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 1E86034DCE4; Mon, 10 Aug 2026 07:51:08 +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=1786348270; cv=none; b=ChZ6GMvhaQiEQ3tkC5w40nGI3zlBCb4yMRhqgaWaZptkZKZvZgCM2caXsNFU7av9quqqDGZSdNx5URsUmG58YDjynSM76J8KgBR4FxM+WF+9/xeRchdn+4iglhgUK8/bpl+2IonLbYsGbFGLl0SLGLWGZDbAdpmdfJuQZvtZCVs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786348270; c=relaxed/simple; bh=WpYittFGbe38+Tijb7dCiR0c7d2CZ13R8zo+EwCPt8M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jETVTXkFU6u03YS5TGvDg3eyITOasnT8Y5bQUdhshkuT0Q1IuA2UEUHF3MEEUOiQnuO4zZuDrZR8OTCiAe/kPsJD6lsSbvkJIAqWzKVX08rsdc5nRS48uWYt4A4dmjhLSmjxeVUf2NU2EdgBdXf5aqDGgNTgIIt4xPA33ja0Lv8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gnfQ9ms/; 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="gnfQ9ms/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A255D1F000E9; Mon, 10 Aug 2026 07:50:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786348268; bh=vFgRE53dFjQ80+ECIKjoyM+QU0baooTcvpeBj0dahws=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=gnfQ9ms/oThb5Ch9veMgNhrTO6RV+Xy8+ko76jeYeDO+7MNWt7ILUr4VOZYJYH7Fu wmVCF3vqoPq0IqhPjG6f7APbnsF6MnV/j4bQ6a3M03YAOg5IZl5nuPItDjbmWadvOo QvmASc3lZ+x3DL7GHoC+2d2iJ5CyjDwrc80XZ+1fmlDV6W4rWJZODKBNZL5PcEPCoZ Syh4S9RULj74wrAJ3Cbuymlm32GvB8hwxv6sGMHUk5eGQyl6R8veZWNKMHl1PNE5bG aksDlkqqBybU0sP8CFGkGWinj/KCckNtR222zEw9cDtLUaYruayTRszZ35YsJGMBqF H7J6eu2OWuPJA== Message-ID: <0a85b27a-121e-40a3-92b6-3927fc298e4e@kernel.org> Date: Mon, 10 Aug 2026 09:50:48 +0200 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 01/41] KVM: guest_memfd: Introduce per-gmem attributes, use to guard user mappings To: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , Vlastimil Babka Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev References: <20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@google.com> <20260728-gmem-inplace-conversion-v9-1-35f9aec2aed2@google.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: <20260728-gmem-inplace-conversion-v9-1-35f9aec2aed2@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/29/26 02:35, Ackerley Tng via B4 Relay wrote: > From: Sean Christopherson > > Start plumbing in guest_memfd support for in-place private<=>shared > conversions by tracking attributes via a maple tree. KVM currently tracks > private vs. shared attributes on a per-VM basis, which made sense when a > guest_memfd _only_ supported private memory, but tracking per-VM simply > can't work for in-place conversions as the shared/private status of a given > page needs to be per-gmem_inode, not per-VM. > > Use the filemap invalidation lock to protect the maple tree, as taking the > lock for read when faulting in memory (for userspace or the guest) isn't > expected to result in meaningful contention, and using a separate lock > would add significant complexity (avoiding deadlock is quite difficult). > > Co-developed-by: Vishal Annapurve > Signed-off-by: Vishal Annapurve > Co-developed-by: Fuad Tabba > Signed-off-by: Fuad Tabba > Signed-off-by: Sean Christopherson > Tested-by: Shivank Garg > Co-developed-by: Ackerley Tng > Signed-off-by: Ackerley Tng > --- > virt/kvm/guest_memfd.c | 133 ++++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 116 insertions(+), 17 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 0bca42a0b346b..3d6547c5ba9a6 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -4,6 +4,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -33,6 +34,13 @@ struct gmem_inode { > struct list_head gmem_file_list; > > u64 flags; > + /* > + * Every index in this inode, whether memory is populated or > + * not, is tracked in attributes. The entire range of indices, > + * corresponding to the size of this inode, is represented in > + * this maple tree. > + */ > + struct maple_tree attributes; > }; > > static __always_inline struct gmem_inode *GMEM_I(struct inode *inode) > @@ -60,9 +68,25 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) > return gfn - slot->base_gfn + slot->gmem.pgoff; > } > > +static u64 kvm_gmem_interpret_entry(struct inode *inode, void *entry) > +{ > + if (WARN_ON_ONCE(!entry)) { > + bool initially_shared = GMEM_I(inode)->flags & > + GUEST_MEMFD_FLAG_INIT_SHARED; > + > + return initially_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE; We have the calculation of the default attribute here and ... > +static int kvm_gmem_init_inode(struct inode *inode, loff_t size, u64 flags) > +{ > + struct gmem_inode *gi = GMEM_I(inode); > + MA_STATE(mas, &gi->attributes, 0, (size >> PAGE_SHIFT) - 1); > + u64 attrs; > + int r; > + > + inode->i_op = &kvm_gmem_iops; > + inode->i_mapping->a_ops = &kvm_gmem_aops; > + inode->i_mode |= S_IFREG; > + inode->i_size = size; > + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); > + > + /* > + * guest_memfd memory is neither migratable nor swappable: set > + * inaccessible to gate off both. > + */ > + mapping_set_inaccessible(inode->i_mapping); > + WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); > + > + gi->flags = flags; > + > + mt_set_external_lock(&gi->attributes, > + &inode->i_mapping->invalidate_lock); > + > + /* > + * Store default attributes for the entire gmem instance. Ensuring every > + * index is represented in the maple tree at all times simplifies the > + * conversion and merging logic. > + */ > + attrs = gi->flags & GUEST_MEMFD_FLAG_INIT_SHARED ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE; ... here. Worth a helper? kvm_gmem_default_attribute(struct inode *inode) ? Nothing else jumped at me, and I agree with the kvm_gmem_get_attributes() improvement :) -- Cheers, David