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[2003:d8:2f0d:f000:eec9:2b8d:4913:f32a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d7fb051bsm149380305e9.18.2025.06.03.00.42.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Jun 2025 00:42:01 -0700 (PDT) Message-ID: <828fa7bb-8519-4e3f-a334-c1b4ea27fee3@redhat.com> Date: Tue, 3 Jun 2025 09:41:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/5] ram-block-attributes: Introduce RamBlockAttributes to manage RAMBlock with guest_memfd To: "Gupta, Pankaj" , Chenyi Qiang , Alexey Kardashevskiy , Peter Xu , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Michael Roth Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, Williams Dan J , Zhao Liu , Baolu Lu , Gao Chao , Xu Yilun , Li Xiaoyao , =?UTF-8?Q?C=C3=A9dric_Le_Goater?= , Alex Williamson , "Lindgren, Tony" , "Maloor, Kishen" References: <20250530083256.105186-1-chenyi.qiang@intel.com> <20250530083256.105186-5-chenyi.qiang@intel.com> <4105d9ad-176e-423a-9b4f-8308205fe204@amd.com> <9a9bb6bb-f8c0-4849-afb0-7cf5a409dab0@intel.com> <219c32d8-4a5e-4a74-add0-aee56b8dc78b@amd.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.015, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 03.06.25 09:17, Gupta, Pankaj wrote: > +CC Tony & Kishen > >>>>> In this patch series we are only maintaining the bitmap for Ram discard/ >>>>> populate state not for regular guest_memfd private/shared? >>>> >>>> As mentioned in changelog, "In the context of RamDiscardManager, shared >>>> state is analogous to populated, and private state is signified as >>>> discarded." To keep consistent with RamDiscardManager, I used the ram >>>> "populated/discareded" in variable and function names. >>>> >>>> Of course, we can use private/shared if we rename the RamDiscardManager >>>> to something like RamStateManager. But I haven't done it in this series. >>>> Because I think we can also view the bitmap as the state of shared >>>> memory (shared discard/shared populate) at present. The VFIO user only >>>> manipulate the dma map/unmap of shared mapping. (We need to consider how >>>> to extend the RDM framwork to manage the shared/private/discard states >>>> in the future when need to distinguish private and discard states.) >>> >>> As function name 'ram_block_attributes_state_change' is generic. Maybe >>> for now metadata update for only two states (shared/private) is enough >>> as it also aligns with discard vs populate states? >> >> Yes, it is enough to treat the shared/private states align with >> populate/discard at present as the only user is VFIO shared mapping. >> >>> >>> As we would also need the shared vs private state metadata for other >>> COCO operations e.g live migration, so wondering having this metadata >>> already there would be helpful. This also will keep the legacy interface >>> (prior to in-place conversion) consistent (As memory-attributes handling >>> is generic operation anyway). >> >> When live migration in CoCo VMs is introduced, I think it needs to >> distinguish the difference between the states of discard and private. It >> cannot simply skip the discard parts any more and needs special handling >> for private parts. So still, we have to extend the interface if have to >> make it avaiable in advance. > > You mean even the discard and private would need different handling I am pretty sure they would in any case? Shared memory, you can simply copy, private memory has to be extracted + placed differently. If we run into problems with live-migration, we can investigate how to extend the current approach. Just like with memory hotplug / virtio-mem, I shared some ideas on how to make it work, but holding up this work when we don't even know what exactly we will exactly need for other future use cases does not sound too plausible. -- Cheers, David / dhildenb