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Fri, 3 Oct 2025 17:24:04 +0000 (UTC) X-Farcaster-Flow-ID: f44c7b7f-75fc-43b3-8033-16cf4d5d0ded Received: from EX19D022EUC002.ant.amazon.com (10.252.51.137) by EX19MTAEUC001.ant.amazon.com (10.252.51.193) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.20; Fri, 3 Oct 2025 17:24:04 +0000 Received: from [192.168.4.149] (10.106.83.12) by EX19D022EUC002.ant.amazon.com (10.252.51.137) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.20; Fri, 3 Oct 2025 17:24:02 +0000 Message-ID: Date: Fri, 3 Oct 2025 18:23:57 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH 15/34] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory To: Paolo Bonzini , Marc Zyngier , "Oliver Upton" , Huacai Chen , "Michael Ellerman" , Anup Patel , "Paul Walmsley" , Palmer Dabbelt , Albert Ou , Sean Christopherson , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , "Andrew Morton" CC: , , , , , , , , , , Xiaoyao Li , Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , David Matlack , Yu Zhang , Isaku Yamahata , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , "Maciej Szmigiero" , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , "Isaku Yamahata" , "Kirill A. Shutemov" References: <20231105163040.14904-1-pbonzini@redhat.com> <20231105163040.14904-16-pbonzini@redhat.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; keydata= xjMEY+ZIvRYJKwYBBAHaRw8BAQdA9FwYskD/5BFmiiTgktstviS9svHeszG2JfIkUqjxf+/N JU5pa2l0YSBLYWx5YXppbiA8a2FseWF6aW5AYW1hem9uLmNvbT7CjwQTFggANxYhBGhhGDEy BjLQwD9FsK+SyiCpmmTzBQJnrNfABQkFps9DAhsDBAsJCAcFFQgJCgsFFgIDAQAACgkQr5LK IKmaZPOpfgD/exazh4C2Z8fNEz54YLJ6tuFEgQrVQPX6nQ/PfQi2+dwBAMGTpZcj9Z9NvSe1 CmmKYnYjhzGxzjBs8itSUvWIcMsFzjgEY+ZIvRIKKwYBBAGXVQEFAQEHQCqd7/nb2tb36vZt ubg1iBLCSDctMlKHsQTp7wCnEc4RAwEIB8J+BBgWCAAmFiEEaGEYMTIGMtDAP0Wwr5LKIKma ZPMFAmes18AFCQWmz0MCGwwACgkQr5LKIKmaZPNTlQEA+q+rGFn7273rOAg+rxPty0M8lJbT i2kGo8RmPPLu650A/1kWgz1AnenQUYzTAFnZrKSsXAw5WoHaDLBz9kiO5pAK In-Reply-To: <20231105163040.14904-16-pbonzini@redhat.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.106.83.12] X-ClientProxiedBy: EX19D013EUA004.ant.amazon.com (10.252.50.48) To EX19D022EUC002.ant.amazon.com (10.252.51.137) On 05/11/2023 16:30, Paolo Bonzini wrote: > From: Sean Christopherson > > Introduce an ioctl(), KVM_CREATE_GUEST_MEMFD, to allow creating file-based > memory that is tied to a specific KVM virtual machine and whose primary > purpose is to serve guest memory. ... > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index f1a575d39b3b..8f46d757a2c5 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c ... > -static int check_memory_region_flags(const struct kvm_userspace_memory_region2 *mem) > +static int check_memory_region_flags(struct kvm *kvm, > + const struct kvm_userspace_memory_region2 *mem) > { > u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES; > > + if (kvm_arch_has_private_mem(kvm)) > + valid_flags |= KVM_MEM_GUEST_MEMFD; > + > + /* Dirty logging private memory is not currently supported. */ > + if (mem->flags & KVM_MEM_GUEST_MEMFD) > + valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES; I was wondering whether this restriction is still required at this stage or can be lifted in cases where the guest memory is accessible by the host. Specifically, it would be useful to support differential memory snapshots based on dirty page tracking in Firecracker [1] or in live migration. As an experiment, I removed the check and was able to produce a diff snapshot and restore a Firecracker VM from it. [1] https://github.com/firecracker-microvm/firecracker/blob/main/docs/snapshotting/snapshot-support.md#creating-diff-snapshots > + > #ifdef __KVM_HAVE_READONLY_MEM > valid_flags |= KVM_MEM_READONLY; > #endif > @@ -2018,7 +2029,7 @@ int __kvm_set_memory_region(struct kvm *kvm, > int as_id, id; > int r; > > - r = check_memory_region_flags(mem); > + r = check_memory_region_flags(kvm, mem); > if (r) > return r;