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[2003:cb:c708:9d00:edd9:835b:4bfb:2ce3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c8acc02sm3527167f8f.104.2024.12.20.01.22.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Dec 2024 01:22:10 -0800 (PST) Message-ID: <78662fe4-00ce-4927-ab62-4545bb6fc289@redhat.com> Date: Fri, 20 Dec 2024 10:22:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] s390: Convert gmap code to use ptdesc To: Matthew Wilcox , Claudio Imbrenda Cc: linux-mm@kvack.org, linux-s390@vger.kernel.org, "Vishal Moola (Oracle)" References: <20241219162252.1025317-1-willy@infradead.org> <20241219162252.1025317-2-willy@infradead.org> 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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 0B9lDImmRn9hRLfFGVg9jzqHUvB3M0PyJ7mWNHJaFjw_1734686532 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9E9D04000C X-Stat-Signature: fqzremw7be1pxx9ioj6fpjnzjw997s4h X-Rspam-User: X-HE-Tag: 1734686510-853719 X-HE-Meta: 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 07f1sJdQ 8rPfZ31cnJmC3eVWRIynujtXOsL5MW6UNR8t4HIF69rGakm7CnJIktf0lzVwV/jBV3gHX23+wa0hfNSJCCHYfEvAw/2A2cC50Hn5DluDJ8tp+WW88WU1ijpB6Dzt78dscbcRMFsjNeHnPXpBaLcEqbEcVMIOo6aeYTxnY5q13d5KOQsxEobQjyfX09aAPRVGMsX/c118JmA3TXZ9Y3dL8xeltUoiqmWaJVp1KBGeubSiEq/QsBS6bHE7Hi/4zN+SE3+dGByyIrFnx/jPelNTh+4JnNlt2EgTZOWrSPL9MJbY3Od+ZJhF3E4kJd4pX2XjFit4qBWDdetMWU2GchU0IlSNh/p/jLBBmiu2chYUuTrgTXsHxxXlI+YQL8R3oQ/0CUIkX8MUkr1h40S8bwPUfYclTMW3w5Tu9f/p9Vr0U2ZNGcxbu5ACY8nl7U9Vn7khQiVg++gItv7B5QyWrDGReMEcb0w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.015719, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 19.12.24 22:23, Matthew Wilcox wrote: > On Thu, Dec 19, 2024 at 04:22:49PM +0000, Matthew Wilcox (Oracle) wrote: >> There was originally some doubt about whether these page tables >> should be represented by a vanilla struct page or whether they >> should be a ptdesc. As we continue on our quest to shrink >> struct page, we seem to have crossed the line into believing that >> thse page tables should be a ptdesc. At least for now. > > Looking at this patch some more, I'm not sure that pt_index is really > what we should be calling this. Would pt_gmap_addr make sense? If > not, what's the right name? Let me try to refresh my memory. (1) Ordinary gmap for running virtual machines We set it to the guest physical address that this page table is responsible for. So we can easily translate from a given gmap page table + offset back to the guest physical address. We set it for PGD/P4D/PUD/PMD page tables in gmap_alloc_table(), and to 0 for the highest level (which logically corresponds to guest physical address 0: page->index = 0). We really only use it for PMD page tables in __gmap_segment_gaddr(), to calculate the guest physical address. (PTE page tables are shared with the process space page tables, which is why we don't maually allocate them or set/get page->index) (2) Shadow gmaps for nested virtualization We set it to the guest physical address of the page table we are shadowing. Meaning, this gmap page table shadows a page table in guest physical address space, and we have to We set it for all page table levels when shadowing them (when marking the to-be-shadowed page table R/O in the gmap so we can catch modifications). We use it in gmap_shadow_pgt_lookup() to translate from a nested guest physical address to a guest physical address, required to resolve faults for our nested guest. We only used "ptdesc->pt_index" in gmap_shadow_pgt() so far, because there we allocate PTE page tables as a shadow page table (not for user space page tables, though!). Long story short, they are "guest physical addresses", which we simply call "gaddr" in that code. So "pt_gaddr" or "pt_gmap_gaddr" make sense. (we should fixup that one pt_index user) -- Cheers, David / dhildenb