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[2003:cb:c745:2000:5e9f:9789:2c3b:8b3d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43d1fd6b2acsm12455885e9.0.2025.03.14.02.50.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Mar 2025 02:50:29 -0700 (PDT) Message-ID: Date: Fri, 14 Mar 2025 10:50:28 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 6/7] memory: Attach MemoryAttributeManager to guest_memfd-backed RAMBlocks To: 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 , Peng Chao P , Gao Chao , Xu Yilun , Li Xiaoyao References: <20250310081837.13123-1-chenyi.qiang@intel.com> <20250310081837.13123-7-chenyi.qiang@intel.com> <8d9ff645-cfc2-4789-9c13-9275103fbd8c@intel.com> <11d40705-60d8-4ad6-8134-86b393bfae8f@redhat.com> <192a8ed9-fecb-4faa-b179-ed6f9ef18ac8@intel.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: 8bit Received-SPF: pass client-ip=170.10.129.124; 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=-0.001, 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 14.03.25 10:30, Chenyi Qiang wrote: > > > On 3/14/2025 5:00 PM, David Hildenbrand wrote: >> On 14.03.25 09:21, Chenyi Qiang wrote: >>> Hi David & Alexey, >> >> Hi, >> >>> >>> To keep the bitmap aligned, I add the undo operation for >>> set_memory_attributes() and use the bitmap + replay callback to do >>> set_memory_attributes(). Does this change make sense? >> >> I assume you mean this hunk: >> >> +    ret = >> memory_attribute_manager_state_change(MEMORY_ATTRIBUTE_MANAGER(mr->rdm), >> +                                                offset, size, to_private); >> +    if (ret) { >> +        warn_report("Failed to notify the listener the state change of " >> +                    "(0x%"HWADDR_PRIx" + 0x%"HWADDR_PRIx") to %s", >> +                    start, size, to_private ? "private" : "shared"); >> +        args.to_private = !to_private; >> +        if (to_private) { >> +            ret = ram_discard_manager_replay_populated(mr->rdm, §ion, >> + >> kvm_set_memory_attributes_cb, >> +                                                       &args); >> +        } else { >> +            ret = ram_discard_manager_replay_discarded(mr->rdm, §ion, >> + >> kvm_set_memory_attributes_cb, >> +                                                       &args); >> +        } >> +        if (ret) { >> +            goto out_unref; >> +        } >> We should probably document that memory_attribute_state_change() cannot fail with "to_private", so you can simplify it to only handle the "to shared" case. >> >> Why is that undo necessary? The bitmap + listeners should be held in >> sync inside of >> memory_attribute_manager_state_change(). Handling this in the caller >> looks wrong. > > state_change() handles the listener, i.e. VFIO/IOMMU. And the caller > handles the core mm side (guest_memfd set_attribute()) undo if > state_change() failed. Just want to keep the attribute consistent with > the bitmap on both side. Do we need this? If not, the bitmap can only > represent the status of listeners. Ah, so you meant that you effectively want to undo the attribute change, because the state effectively cannot change, and we want to revert the attribute change. That makes sense when we are converting private->shared. BTW, I'm thinking if the orders should be the following (with in-place conversion in mind where we would mmap guest_memfd for the shared memory parts). On private -> shared conversion: (1) change_attribute() (2) state_change(): IOMMU pins shared memory (3) restore_attribute() if it failed On shared -> private conversion (1) state_change(): IOMMU unpins shared memory (2) change_attribute(): can convert in-place because there are not pins I'm wondering if the whole attribute change could actually be a listener, invoked by the memory_attribute_manager_state_change() call itself in the right order. We'd probably need listener priorities, and invoke them in reverse order on shared -> private conversion. Just an idea to get rid of the manual ram_discard_manager_replay_discarded() call in your code. -- Cheers, David / dhildenbh