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[2003:d8:2f34:a300:1c2c:f35e:e8e5:488e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d7fb00ccsm136512135e9.17.2025.06.02.14.10.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Jun 2025 14:10:52 -0700 (PDT) Message-ID: <2278c8cb-a547-4f8d-a8fb-cce38fa3b5f2@redhat.com> Date: Mon, 2 Jun 2025 23:10:51 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: Chenyi Qiang , Alexey Kardashevskiy , Peter Xu , Gupta Pankaj , 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 References: <20250530083256.105186-1-chenyi.qiang@intel.com> <20250530083256.105186-5-chenyi.qiang@intel.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250530083256.105186-5-chenyi.qiang@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 30.05.25 10:32, Chenyi Qiang wrote: > Commit 852f0048f3 ("RAMBlock: make guest_memfd require uncoordinated > discard") highlighted that subsystems like VFIO may disable RAM block > discard. However, guest_memfd relies on discard operations for page > conversion between private and shared memory, potentially leading to > the stale IOMMU mapping issue when assigning hardware devices to > confidential VMs via shared memory. To address this and allow shared > device assignement, it is crucial to ensure the VFIO system refreshes > its IOMMU mappings. > > RamDiscardManager is an existing interface (used by virtio-mem) to > adjust VFIO mappings in relation to VM page assignment. Effectively page > conversion is similar to hot-removing a page in one mode and adding it > back in the other. Therefore, similar actions are required for page > conversion events. Introduce the RamDiscardManager to guest_memfd to > facilitate this process. > > Since guest_memfd is not an object, it cannot directly implement the > RamDiscardManager interface. Implementing it in HostMemoryBackend is > not appropriate because guest_memfd is per RAMBlock, and some RAMBlocks > have a memory backend while others do not. Notably, virtual BIOS > RAMBlocks using memory_region_init_ram_guest_memfd() do not have a > backend. > > To manage RAMBlocks with guest_memfd, define a new object named > RamBlockAttributes to implement the RamDiscardManager interface. This > object can store the guest_memfd information such as bitmap for shared > memory and the registered listeners for event notification. In the > context of RamDiscardManager, shared state is analogous to populated, and > private state is signified as discarded. To notify the conversion events, > a new state_change() helper is exported for the users to notify the > listeners like VFIO, so that VFIO can dynamically DMA map/unmap the > shared mapping. > > Note that the memory state is tracked at the host page size granularity, > as the minimum conversion size can be one page per request and VFIO > expects the DMA mapping for a specific iova to be mapped and unmapped > with the same granularity. Confidential VMs may perform partial > conversions, such as conversions on small regions within larger ones. > To prevent such invalid cases and until DMA mapping cut operation > support is available, all operations are performed with 4K granularity. > > In addition, memory conversion failures cause QEMU to quit instead of > resuming the guest or retrying the operation at present. It would be > future work to add more error handling or rollback mechanisms once > conversion failures are allowed. For example, in-place conversion of > guest_memfd could retry the unmap operation during the conversion from > shared to private. For now, keep the complex error handling out of the > picture as it is not required. > > Signed-off-by: Chenyi Qiang > --- > Changes in v6: > - Change the object type name from RamBlockAttribute to > RamBlockAttributes. (David) > - Save the associated RAMBlock instead MemoryRegion in > RamBlockAttributes. (David) > - Squash the state_change() helper introduction in this commit as > well as the mixture conversion case handling. (David) > - Change the block_size type from int to size_t and some cleanup in > validation check. (Alexey) > - Add a tracepoint to track the state changes. (Alexey) > > Changes in v5: > - Revert to use RamDiscardManager interface instead of introducing > new hierarchy of class to manage private/shared state, and keep > using the new name of RamBlockAttribute compared with the > MemoryAttributeManager in v3. > - Use *simple* version of object_define and object_declare since the > state_change() function is changed as an exported function instead > of a virtual function in later patch. > - Move the introduction of RamBlockAttribute field to this patch and > rename it to ram_shared. (Alexey) > - call the exit() when register/unregister failed. (Zhao) > - Add the ram-block-attribute.c to Memory API related part in > MAINTAINERS. > > Changes in v4: > - Change the name from memory-attribute-manager to > ram-block-attribute. > - Implement the newly-introduced PrivateSharedManager instead of > RamDiscardManager and change related commit message. > - Define the new object in ramblock.h instead of adding a new file. > --- > MAINTAINERS | 1 + > include/system/ramblock.h | 21 ++ > system/meson.build | 1 + > system/ram-block-attributes.c | 480 ++++++++++++++++++++++++++++++++++ > system/trace-events | 3 + > 5 files changed, 506 insertions(+) > create mode 100644 system/ram-block-attributes.c > > diff --git a/MAINTAINERS b/MAINTAINERS > index 6dacd6d004..8ec39aa7f8 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -3149,6 +3149,7 @@ F: system/memory.c > F: system/memory_mapping.c > F: system/physmem.c > F: system/memory-internal.h > +F: system/ram-block-attributes.c > F: scripts/coccinelle/memory-region-housekeeping.cocci > > Memory devices > diff --git a/include/system/ramblock.h b/include/system/ramblock.h > index d8a116ba99..1bab9e2dac 100644 > --- a/include/system/ramblock.h > +++ b/include/system/ramblock.h > @@ -22,6 +22,10 @@ > #include "exec/cpu-common.h" > #include "qemu/rcu.h" > #include "exec/ramlist.h" > +#include "system/hostmem.h" > + > +#define TYPE_RAM_BLOCK_ATTRIBUTES "ram-block-attributes" > +OBJECT_DECLARE_SIMPLE_TYPE(RamBlockAttributes, RAM_BLOCK_ATTRIBUTES) > > struct RAMBlock { > struct rcu_head rcu; > @@ -91,4 +95,21 @@ struct RAMBlock { > ram_addr_t postcopy_length; > }; > > +struct RamBlockAttributes { > + Object parent; > + > + RAMBlock *ram_block; > + > + /* 1-setting of the bitmap represents ram is populated (shared) */ > + unsigned bitmap_size; > + unsigned long *bitmap; So, initially, all memory starts out as private, correct? I guess this mimics what kvm_set_phys_mem() ends up doing, when it does the kvm_set_memory_attributes_private() call. So there is a short period of inconsistency, between creating the RAMBlock and mapping it into the PA space. It might be wroth spelling that out / documenting it somewhere. -- Cheers, David / dhildenb