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(p200300cbc72237006501892506f9fcdc.dip0.t-ipconnect.de. [2003:cb:c722:3700:6501:8925:6f9:fcdc]) by smtp.gmail.com with ESMTPSA id d9-20020adffd89000000b0033330846e76sm8983550wrr.86.2023.12.04.01.52.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Dec 2023 01:52:01 -0800 (PST) Message-ID: <5f65ec5d-7079-4b32-8e40-b9ece3bdd47c@redhat.com> Date: Mon, 4 Dec 2023 10:52:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 07/70] physmem: Relax the alignment check of host_startaddr in ram_block_discard_range() Content-Language: en-US To: Xiaoyao Li , Paolo Bonzini , Igor Mammedov , "Michael S . Tsirkin" , Marcel Apfelbaum , Richard Henderson , Peter Xu , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Cornelia Huck , =?UTF-8?Q?Daniel_P_=2E_Berrang=C3=A9?= , Eric Blake , Markus Armbruster , Marcelo Tosatti Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, Michael Roth , Sean Christopherson , Claudio Fontana , Gerd Hoffmann , Isaku Yamahata , Chenyi Qiang References: <20231115071519.2864957-1-xiaoyao.li@intel.com> <20231115071519.2864957-8-xiaoyao.li@intel.com> <00b533ee-fbb1-4e78-bc8b-b6d87761bb92@intel.com> <419ffc61-fcd7-4940-a550-9ce6c6a14e1b@redhat.com> <4fe173c9-6be2-4850-a5a4-d2b9299278f9@intel.com> <309118fb-5737-40cb-b34d-916546443d4d@intel.com> From: David Hildenbrand 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: <309118fb-5737-40cb-b34d-916546443d4d@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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=-0.001, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 04.12.23 08:53, Xiaoyao Li wrote: > On 12/4/2023 3:35 PM, Xiaoyao Li wrote: >> On 11/20/2023 5:56 PM, David Hildenbrand wrote: >>> On 16.11.23 03:56, Xiaoyao Li wrote: >>>> On 11/16/2023 2:20 AM, David Hildenbrand wrote: >>>>> On 15.11.23 08:14, Xiaoyao Li wrote: >>>>>> Commit d3a5038c461 ("exec: ram_block_discard_range") introduced >>>>>> ram_block_discard_range() which grabs some code from >>>>>> ram_discard_range(). However, during code movement, it changed >>>>>> alignment >>>>>> check of host_startaddr from qemu_host_page_size to rb->page_size. >>>>>> >>>>>> When ramblock is back'ed by hugepage, it requires the startaddr to be >>>>>> huge page size aligned, which is a overkill. e.g., TDX's >>>>>> private-shared >>>>>> page conversion is done at 4KB granularity. Shared page is discarded >>>>>> when it gets converts to private and when shared page back'ed by >>>>>> hugepage it is going to fail on this check. >>>>>> >>>>>> So change to alignment check back to qemu_host_page_size. >>>>>> >>>>>> Signed-off-by: Xiaoyao Li >>>>>> --- >>>>>> Changes in v3: >>>>>>    - Newly added in v3; >>>>>> --- >>>>>>    system/physmem.c | 2 +- >>>>>>    1 file changed, 1 insertion(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/system/physmem.c b/system/physmem.c >>>>>> index c56b17e44df6..8a4e42c7cf60 100644 >>>>>> --- a/system/physmem.c >>>>>> +++ b/system/physmem.c >>>>>> @@ -3532,7 +3532,7 @@ int ram_block_discard_range(RAMBlock *rb, >>>>>> uint64_t start, size_t length) >>>>>>        uint8_t *host_startaddr = rb->host + start; >>>>>> -    if (!QEMU_PTR_IS_ALIGNED(host_startaddr, rb->page_size)) { >>>>>> +    if (!QEMU_PTR_IS_ALIGNED(host_startaddr, qemu_host_page_size)) { >>>>> >>>>> For your use cases, rb->page_size should always match >>>>> qemu_host_page_size. >>>>> >>>>> IIRC, we only set rb->page_size to different values for hugetlb. And >>>>> guest_memfd does not support hugetlb. >>>>> >>>>> Even if QEMU is using THP, rb->page_size should 4k. >>>>> >>>>> Please elaborate how you can actually trigger that. From what I recall, >>>>> guest_memfd is not compatible with hugetlb. >>>> >>>> It's the shared memory that can be back'ed by hugetlb. >>> >>> Serious question: does that configuration make any sense to support at >>> this point? I claim: no. >>> >>>> >>>> Later patch 9 introduces ram_block_convert_page(), which will discard >>>> shared memory when it gets converted to private. TD guest can request >>>> convert a 4K to private while the page is previously back'ed by hugetlb >>>> as 2M shared page. >>> >>> So you can call ram_block_discard_guest_memfd_range() on subpage >>> basis, but not ram_block_discard_range(). >>> >>> ram_block_convert_range() would have to thought that that >>> (questionable) combination of hugetlb for shmem and ordinary pages for >>> guest_memfd cannot discard shared memory. >>> >>> And it probably shouldn't either way. There are other problems when >>> not using hugetlb along with preallocation. >> >> If I understand correctly, preallocation needs to be enabled for >> hugetlb. And in preallocation case, it doesn't need to discard memory. >> Is it correct? Yes The downside is that we'll end up with double-memory consumption. But if/how to optimize that in this case ca be left for future work. >> >>> The check in ram_block_discard_range() is correct, whoever ends up >>> calling it has to stop calling it. >>> >> > So, I need add logic to ram_block_discard_page() that if the size of > > Sorry, I made a typo. > > Correct myself, s/ram_block_discard_page()/ram_block_convert_range() Yes, just leave any shared memory backend that uses hugetlb alone. -- Cheers, David / dhildenb