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[2003:cb:c706:2000:e44c:bc46:d8d3:be5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259d5923sm21604078f8f.74.2025.02.20.11.39.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Feb 2025 11:39:55 -0800 (PST) Message-ID: <0d761daf-174d-487f-80fe-09b04902006f@redhat.com> Date: Thu, 20 Feb 2025 20:39:53 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 1/2] system/memory: Allow creating IOMMU mappings from RAM discard populate notifiers To: Jean-Philippe Brucker , philmd@linaro.org, peterx@redhat.com, pbonzini@redhat.com, peter.maydell@linaro.org, Chenyi Qiang Cc: qemu-arm@nongnu.org, qemu-devel@nongnu.org References: <20250220161320.518450-2-jean-philippe@linaro.org> <20250220161320.518450-3-jean-philippe@linaro.org> 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: <20250220161320.518450-3-jean-philippe@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.457, 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 20.02.25 17:13, Jean-Philippe Brucker wrote: > For Arm CCA we'd like the guest_memfd discard notifier to call the IOMMU > notifiers and create e.g. VFIO mappings. The default VFIO discard > notifier isn't sufficient for CCA because the DMA addresses need a > translation (even without vIOMMU). > > At the moment: > * guest_memfd_state_change() calls the populate() notifier > * the populate notifier() calls IOMMU notifiers > * the IOMMU notifier handler calls memory_get_xlat_addr() to get a VA > * it calls ram_discard_manager_is_populated() which fails. > > guest_memfd_state_change() only changes the section's state after > calling the populate() notifier. We can't easily invert the order of > operation because it uses the old state bitmap to know which pages need > the populate() notifier. I assume we talk about this code: [1] [1] https://lkml.kernel.org/r/20250217081833.21568-1-chenyi.qiang@intel.com +static int memory_attribute_state_change(MemoryAttributeManager *mgr, uint64_t offset, + uint64_t size, bool shared_to_private) +{ + int block_size = memory_attribute_manager_get_block_size(mgr); + int ret = 0; + + if (!memory_attribute_is_valid_range(mgr, offset, size)) { + error_report("%s, invalid range: offset 0x%lx, size 0x%lx", + __func__, offset, size); + return -1; + } + + if ((shared_to_private && memory_attribute_is_range_discarded(mgr, offset, size)) || + (!shared_to_private && memory_attribute_is_range_populated(mgr, offset, size))) { + return 0; + } + + if (shared_to_private) { + memory_attribute_notify_discard(mgr, offset, size); + } else { + ret = memory_attribute_notify_populate(mgr, offset, size); + } + + if (!ret) { + unsigned long first_bit = offset / block_size; + unsigned long nbits = size / block_size; + + g_assert((first_bit + nbits) <= mgr->bitmap_size); + + if (shared_to_private) { + bitmap_clear(mgr->shared_bitmap, first_bit, nbits); + } else { + bitmap_set(mgr->shared_bitmap, first_bit, nbits); + } + + return 0; + } + + return ret; +} Then, in memory_attribute_notify_populate(), we walk the bitmap again. Why? We just checked that it's all in the expected state, no? virtio-mem doesn't handle it that way, so I'm curious why we would have to do it here? > > For now add a flag to the IOMMU notifier to tell memory_get_xlat_addr() > that we're aware of the RAM discard manager state. > > Signed-off-by: Jean-Philippe Brucker > --- > > Definitely not the prettiest hack, any idea how to do this cleanly? > --- > include/exec/memory.h | 5 +++++ > system/memory.c | 3 ++- > 2 files changed, 7 insertions(+), 1 deletion(-) > > diff --git a/include/exec/memory.h b/include/exec/memory.h > index 9f73b59867..6fcd98fe58 100644 > --- a/include/exec/memory.h > +++ b/include/exec/memory.h > @@ -116,6 +116,11 @@ typedef enum { > IOMMU_RO = 1, > IOMMU_WO = 2, > IOMMU_RW = 3, > + /* > + * Allow mapping a discarded page, because we're in the process of > + * populating it. > + */ > + IOMMU_POPULATING = 4, > } IOMMUAccessFlags; > > #define IOMMU_ACCESS_FLAG(r, w) (((r) ? IOMMU_RO : 0) | ((w) ? IOMMU_WO : 0)) > diff --git a/system/memory.c b/system/memory.c > index 4c829793a0..8e884f9c15 100644 > --- a/system/memory.c > +++ b/system/memory.c > @@ -2221,7 +2221,8 @@ bool memory_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr, > * Disallow that. vmstate priorities make sure any RamDiscardManager > * were already restored before IOMMUs are restored. > */ > - if (!ram_discard_manager_is_populated(rdm, &tmp)) { > + if (!(iotlb->perm & IOMMU_POPULATING) && > + !ram_discard_manager_is_populated(rdm, &tmp)) { > error_setg(errp, "iommu map to discarded memory (e.g., unplugged" > " via virtio-mem): %" HWADDR_PRIx "", > iotlb->translated_addr); -- Cheers, David / dhildenb