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(p200300cbc70b7a009ccd0493d8e29ac8.dip0.t-ipconnect.de. [2003:cb:c70b:7a00:9ccd:493:d8e2:9ac8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-433cde114d5sm23620125e9.17.2024.11.22.03.03.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Nov 2024 03:03:15 -0800 (PST) Message-ID: <0903abca-42f5-4ca7-8c81-070e7669f996@redhat.com> Date: Fri, 22 Nov 2024 12:03:14 +0100 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/2] mm: guestmem: Convert address_space operations to guestmem library To: michael.day@amd.com, Elliot Berman , Paolo Bonzini , Andrew Morton , Sean Christopherson , Fuad Tabba , Ackerley Tng , Mike Rapoport , "H. Peter Anvin" , "Matthew Wilcox (Oracle)" , Jonathan Corbet , Trond Myklebust , Anna Schumaker , Mike Marshall , Martin Brandenburg , Alexander Viro , Christian Brauner , Jan Kara Cc: James Gowans , linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-nfs@vger.kernel.org, devel@lists.orangefs.org, linux-arm-kernel@lists.infradead.org References: <20241120-guestmem-library-v4-0-0c597f733909@quicinc.com> <20241120-guestmem-library-v4-2-0c597f733909@quicinc.com> <20241120145527130-0800.eberman@hu-eberman-lv.qualcomm.com> <3349f838-2c73-4ef0-aa30-a21e41fb39e5@amd.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: <3349f838-2c73-4ef0-aa30-a21e41fb39e5@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 21.11.24 18:40, Mike Day wrote: > > > On 11/21/24 10:43, Elliot Berman wrote: >> On Wed, Nov 20, 2024 at 10:12:08AM -0800, Elliot Berman wrote: >>> diff --git a/mm/guestmem.c b/mm/guestmem.c >>> new file mode 100644 >>> index 0000000000000000000000000000000000000000..19dd7e5d498f07577ec5cec5b52055f7435980f4 >>> --- /dev/null >>> +++ b/mm/guestmem.c >>> @@ -0,0 +1,196 @@ >>> +// SPDX-License-Identifier: GPL-2.0-only >>> +/* >>> + * guestmem library >>> + * >>> + * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved. >>> + */ >>> + >>> +#include >>> +#include >>> +#include >>> +#include >>> + >>> +struct guestmem { >>> + const struct guestmem_ops *ops; >>> +}; >>> + >>> +static inline struct guestmem *folio_to_guestmem(struct folio *folio) >>> +{ >>> + struct address_space *mapping = folio->mapping; >>> + >>> + return mapping->i_private_data; >>> +} >>> + >>> +static inline bool __guestmem_release_folio(struct address_space *mapping, >>> + struct folio *folio) >>> +{ >>> + struct guestmem *gmem = mapping->i_private_data; >>> + struct list_head *entry; >>> + >>> + if (gmem->ops->release_folio) { >>> + list_for_each(entry, &mapping->i_private_list) { >>> + if (!gmem->ops->release_folio(entry, folio)) >>> + return false; >>> + } >>> + } >>> + >>> + return true; >>> +} >>> + >>> +static inline int >>> +__guestmem_invalidate_begin(struct address_space *const mapping, pgoff_t start, >>> + pgoff_t end) >>> +{ >>> + struct guestmem *gmem = mapping->i_private_data; >>> + struct list_head *entry; >>> + int ret = 0; >>> + >>> + list_for_each(entry, &mapping->i_private_list) { >>> + ret = gmem->ops->invalidate_begin(entry, start, end); >>> + if (ret) >>> + return ret; >>> + } >>> + >>> + return 0; >>> +} >>> + >>> +static inline void >>> +__guestmem_invalidate_end(struct address_space *const mapping, pgoff_t start, >>> + pgoff_t end) >>> +{ >>> + struct guestmem *gmem = mapping->i_private_data; >>> + struct list_head *entry; >>> + >>> + if (gmem->ops->invalidate_end) { >>> + list_for_each(entry, &mapping->i_private_list) >>> + gmem->ops->invalidate_end(entry, start, end); >>> + } >>> +} >>> + >>> +static void guestmem_free_folio(struct address_space *mapping, >>> + struct folio *folio) >>> +{ >>> + WARN_ON_ONCE(!__guestmem_release_folio(mapping, folio)); >>> +} >>> + >>> +static int guestmem_error_folio(struct address_space *mapping, >>> + struct folio *folio) >>> +{ >>> + pgoff_t start, end; >>> + int ret; >>> + >>> + filemap_invalidate_lock_shared(mapping); >>> + >>> + start = folio->index; >>> + end = start + folio_nr_pages(folio); >>> + >>> + ret = __guestmem_invalidate_begin(mapping, start, end); >>> + if (ret) >>> + goto out; >>> + >>> + /* >>> + * Do not truncate the range, what action is taken in response to the >>> + * error is userspace's decision (assuming the architecture supports >>> + * gracefully handling memory errors). If/when the guest attempts to >>> + * access a poisoned page, kvm_gmem_get_pfn() will return -EHWPOISON, >>> + * at which point KVM can either terminate the VM or propagate the >>> + * error to userspace. >>> + */ >>> + >>> + __guestmem_invalidate_end(mapping, start, end); >>> + >>> +out: >>> + filemap_invalidate_unlock_shared(mapping); >>> + return ret ? MF_DELAYED : MF_FAILED; >>> +} >>> + >>> +static int guestmem_migrate_folio(struct address_space *mapping, >>> + struct folio *dst, struct folio *src, >>> + enum migrate_mode mode) >>> +{ >>> + WARN_ON_ONCE(1); >>> + return -EINVAL; >>> +} >>> + >>> +static const struct address_space_operations guestmem_aops = { >>> + .dirty_folio = noop_dirty_folio, >>> + .free_folio = guestmem_free_folio, >>> + .error_remove_folio = guestmem_error_folio, >>> + .migrate_folio = guestmem_migrate_folio, >>> +}; >>> + >>> +int guestmem_attach_mapping(struct address_space *mapping, >>> + const struct guestmem_ops *const ops, >>> + struct list_head *data) >>> +{ >>> + struct guestmem *gmem; >>> + >>> + if (mapping->a_ops == &guestmem_aops) { >>> + gmem = mapping->i_private_data; >>> + if (gmem->ops != ops) >>> + return -EINVAL; >>> + >>> + goto add; >>> + } >>> + >>> + gmem = kzalloc(sizeof(*gmem), GFP_KERNEL); >>> + if (!gmem) >>> + return -ENOMEM; >>> + >>> + gmem->ops = ops; >>> + >>> + mapping->a_ops = &guestmem_aops; >>> + mapping->i_private_data = gmem; >>> + >>> + mapping_set_gfp_mask(mapping, GFP_HIGHUSER); >>> + mapping_set_inaccessible(mapping); >>> + /* Unmovable mappings are supposed to be marked unevictable as well. */ >>> + WARN_ON_ONCE(!mapping_unevictable(mapping)); >>> + >>> +add: >>> + list_add(data, &mapping->i_private_list); >>> + return 0; >>> +} >>> +EXPORT_SYMBOL_GPL(guestmem_attach_mapping); >>> + >>> +void guestmem_detach_mapping(struct address_space *mapping, >>> + struct list_head *data) >>> +{ >>> + list_del(data); >>> + >>> + if (list_empty(&mapping->i_private_list)) { >>> + kfree(mapping->i_private_data); >> >> Mike was helping me test this out for SEV-SNP. They helped find a bug >> here. Right now, when the file closes, KVM calls >> guestmem_detach_mapping() which will uninstall the ops. When that >> happens, it's not necessary that all of the folios aren't removed from >> the filemap yet Yes, that's the real issue. There either must be some lifetime tracking (kfree() after the mapping is completely unused), or you have to tear it all down before you mess with the mapping. >> >> There are a few approaches I could take: >> >> 1. Create a guestmem superblock so I can register guestmem-specific >> destroy_inode() to do the kfree() above. This requires a lot of >> boilerplate code, and I think it's not preferred approach. >> 2. Update how KVM tracks the memory so it is back in "shared" state when >> the file closes. This requires some significant rework about the page >> state compared to current guest_memfd. That rework might be useful >> for the shared/private state machine. >> 3. Call truncate_inode_pages(mapping, 0) to force pages to be freed >> here. It's might be possible that a page is allocated after this >> point. In order for that to be a problem, KVM would need to update >> RMP entry as guest-owned, and I don't believe that's possible after >> the last guestmem_detach_mapping(). >> >> My preference is to go with #3 as it was the most easy thing to do. > > #3 is my preference as well. The semantics are that the guest is "closing" the gmem > object, which means all the memory is being released from the guest. Agreed. -- Cheers, David / dhildenb