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Wed, 12 Feb 2020 12:16:59 +0000 (UTC) Received: from [10.36.117.92] (ovpn-117-92.ams2.redhat.com [10.36.117.92]) by smtp.corp.redhat.com (Postfix) with ESMTP id A8224391; Wed, 12 Feb 2020 12:16:56 +0000 (UTC) Subject: Re: [PATCH v2 RFC] KVM: s390/interrupt: do not pin adapter interrupt pages To: Christian Borntraeger Cc: Ulrich.Weigand@de.ibm.com, aarcange@redhat.com, akpm@linux-foundation.org, cohuck@redhat.com, frankja@linux.vnet.ibm.com, gor@linux.ibm.com, imbrenda@linux.ibm.com, kvm@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, mimu@linux.ibm.com, thuth@redhat.com, "dgilbert@redhat.com" References: <567B980B-BDA5-4EF3-A96E-1542D11F2BD4@redhat.com> <20200211092341.3965-1-borntraeger@de.ibm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <01d1c188-38fb-e405-83d7-6184adccba5a@redhat.com> Date: Wed, 12 Feb 2020 13:16:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200211092341.3965-1-borntraeger@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > + /* > + * We resolve the gpa to hva when setting the IRQ routing. If userspa= ce > + * decides to mess with the memslots it better also updates the irq > + * routing. Otherwise we will write to the wrong userspace address. > + */ I guess this is just as old handling, where a page was pinned. But slightly better :) So the pages are definitely part of guest memory. Fun stuff: If (a nasty) guest (in current code) zappes this page using balloon inflation and the page is re-accessed (e.g., by the guest or by the host), a new page will be faulted in, and there will be an inconsistency between what the guest/user space sees and what this code sees. Going via the user space address looks cleaner. Now, with postcopy live migration, we will also zap all guest memory before starting the guest, I do wonder if that produces a similar inconsistency ... usually, when pages are pinned in the kernel, we inhibit the balloon and implicitly also postcopy. If so, this actually fixes an issue. But might depend on the order things are initialized in user space. Or I am messing up things :) [...] > static int kvm_s390_adapter_unmap(struct kvm *kvm, unsigned int id, __= u64 addr) > { > - struct s390_io_adapter *adapter =3D get_io_adapter(kvm, id); > - struct s390_map_info *map, *tmp; > - int found =3D 0; > - > - if (!adapter || !addr) > - return -EINVAL; > - > - down_write(&adapter->maps_lock); > - list_for_each_entry_safe(map, tmp, &adapter->maps, list) { > - if (map->guest_addr =3D=3D addr) { > - found =3D 1; > - atomic_dec(&adapter->nr_maps); > - list_del(&map->list); > - put_page(map->page); > - kfree(map); > - break; > - } > - } > - up_write(&adapter->maps_lock); > - > - return found ? 0 : -EINVAL; > + return 0; Can we get rid of this function? > } > +static struct page *get_map_page(struct kvm *kvm, > + struct s390_io_adapter *adapter, > + u64 uaddr) > { > - struct s390_map_info *map; > + struct page *page; > + int ret; > =20 > if (!adapter) > return NULL; > - > - list_for_each_entry(map, &adapter->maps, list) { > - if (map->guest_addr =3D=3D addr) > - return map; > - } > - return NULL; > + page =3D NULL; struct page *page =3D NULL; > + if (!uaddr) > + return NULL; > + down_read(&kvm->mm->mmap_sem); > + ret =3D get_user_pages_remote(NULL, kvm->mm, uaddr, 1, FOLL_WRITE, > + &page, NULL, NULL); > + if (ret < 1) > + page =3D NULL; Is that really necessary? According to the doc, pinned pages are stored to the array. ret < 1 means "no pages" were pinned, so nothing should be stored. --=20 Thanks, David / dhildenb