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 13F4054A7CF; Wed, 9 Sep 2026 15:47:28 +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=1788968850; cv=none; b=Pj+G59KgDB8x322+DLVFQxDvrMXbfUCWItLiAWJjOXvbnQDWKxvhtpFUwQRQm4+u7eUnrOOtYqupvMCeyPgjPV6XcoFpPPTL9mJrgUqHLqwj7WIkiL6esXIVIuDNKwadxin1ALmRSvDJHwFN2dHWr7iodlAskhVC9oaH7hA3gcs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788968850; c=relaxed/simple; bh=wKulJA5WaTPngsbarg3L1eHbRUXM4vQLL+RcO+gzAik=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OjdZIuWUlz/b8ok5oTQz84uVhmnYHFjWz0pUt9Q+KFj/+hU6dAYd5mI4NrHWtcLlA3tSlh6/qiPDuk/Bd9oRKBSMjMYBLJjd0wJ1985NZkAdJEYbXVTcICQrQiqM3IrT+1Pgo5K7+C5RpGdgskd0geDq+hYCD2+G4TUfv0OIsd0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=U3hCuoRu; 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="U3hCuoRu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E2261F00A3A; Wed, 9 Sep 2026 15:47:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788968848; bh=UPlEwDATkKsdnhPipJ/RnZzY8Ea9kWNibxkB8VtNG/0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=U3hCuoRuyOU4wAxDDZm3tqdyOYQ78j7gRNdobasTRZ3EyQ1BOVPWRhY4lOwidY6lo jq7/GojnIOSmrMOZPidFbFfVXltqqH3hfyKAwIoSo7hIvZWMS12AMK1eTt4Icp05Ps JQjzUXEXm7//EFMSL5ari8t3V7m5xzxzctzZmvfkBzmk92jg/g4Hfh5ihWaKQ/WXZ8 EDZp+Cy4KdsgXxo8l9uIDUArYMHe+dXYGoIlLsxIpPjshMXO6NyowsV73R9NqaowsS 9mKET6R5YNCOe7BOvcBMmZWibyg1/HGmGF4bHeaXacxPQ7N7hXNuof4OonTVGbPLlS jd3+jD0Y+b5Mg== Message-ID: Date: Wed, 9 Sep 2026 17:47:07 +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 v12 23/45] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes 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, 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 , tarunsahu@google.com, Randy Dunlap , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Fuad Tabba 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, Xiaoyao Li References: <20260830-gmem-inplace-conversion-v12-0-85e5fd25252a@google.com> <20260830-gmem-inplace-conversion-v12-23-85e5fd25252a@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: <20260830-gmem-inplace-conversion-v12-23-85e5fd25252a@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/31/26 02:25, Ackerley Tng via B4 Relay wrote: > From: Sean Christopherson > > Allow the user to disable KVM_VM_MEMORY_ATTRIBUTES even when KVM supports > PRIVATE and SHARED attributes, and expose gmem_in_place_conversion as a > module parameter when per-VM attributes are supported. I.e. let userspace > enable in-place PRIVATE<=>SHARED conversion of guest_memfd pages. > > Provide both a Kconfig option and a (conditional) module param so that > deployments that use a custom kernel can fully disable per-VM tracking, > while not forcing distros to ship two separate kernels in order to provide > backwards compatibility for downstream users. > > Don't allow running VMs with mixed tracking for a given instance of KVM, > i.e. disallow toggling the module param after KVM is loaded, as the extra > complexity needed to handle per-VM behavior far outweighs any potential > benefit. E.g. neither TDX nor SNP supports live migration, so in effect > the requirement is that existing deployments that want to support both the > old and the new models would need to tell their VMM which flavor of > tracking to use. > > Signed-off-by: Sean Christopherson > Reviewed-by: Fuad Tabba > Tested-by: Shivank Garg > [Define module_param only if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is enabled] > Suggested-by: Xiaoyao Li > Reviewed-by: Xiaoyao Li > Co-developed-by: Ackerley Tng > Signed-off-by: Ackerley Tng > --- > Documentation/admin-guide/kernel-parameters.txt | 25 +++++++++++++++++++++++++ > arch/x86/include/asm/kvm_host.h | 4 +++- > arch/x86/kvm/Kconfig | 14 ++++++++++---- > virt/kvm/kvm_main.c | 5 ++++- > 4 files changed, 42 insertions(+), 6 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 68647ff4bdd24..b5719714458fb 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3156,6 +3156,31 @@ Kernel parameters > kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. > Default is false (don't support). > > + kvm.gmem_in_place_conversion= > + [KVM] Controls whether KVM enables in-place conversion > + support for guest_memfd and tracks the private/shared > + state of memory per guest_memfd instead of per VM. > + > + If enabled, KVM enables the KVM_SET_MEMORY_ATTRIBUTES2 > + ioctl on guest_memfd file descriptors and disables the > + legacy VM-scoped KVM_SET_MEMORY_ATTRIBUTES ioctl for > + private memory state tracking. Only the > + KVM_MEMORY_ATTRIBUTE_PRIVATE attribute moves to > + per-guest_memfd tracking; other attributes remain > + per-VM. > + > + This parameter toggles KVM's in-place conversion > + capability support. Whether a VMM uses separate backends > + or out-of-place memory management is determined by > + userspace VMM design. > + > + Note, this parameter is only available when > + CONFIG_KVM_VM_MEMORY_ATTRIBUTES=y. When > + CONFIG_KVM_VM_MEMORY_ATTRIBUTES is not set, in-place > + conversion is unconditionally enabled. > + > + Default is Y (on). With the doc fixed Acked-by: David Hildenbrand (Arm) -- Cheers, David