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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 12 Feb 2020 12:22:55 -0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06avi18878370.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01CCMr0846661906 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 12 Feb 2020 12:22:53 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 86C494C058; Wed, 12 Feb 2020 12:22:53 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1D7034C04A; Wed, 12 Feb 2020 12:22:53 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.71]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 12 Feb 2020 12:22:53 +0000 (GMT) Subject: Re: [PATCH v2 RFC] KVM: s390/interrupt: do not pin adapter interrupt pages To: David Hildenbrand 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> <01d1c188-38fb-e405-83d7-6184adccba5a@redhat.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <01d1c188-38fb-e405-83d7-6184adccba5a@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 20021212-0016-0000-0000-000002E620AF X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20021212-0017-0000-0000-000033491BDB Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-12_06:2020-02-11,2020-02-12 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 impostorscore=0 lowpriorityscore=0 malwarescore=0 bulkscore=0 clxscore=1015 mlxlogscore=587 mlxscore=0 suspectscore=0 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002120100 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: On 12.02.20 13:16, David Hildenbrand wrote: > >> + /* >> + * We resolve the gpa to hva when setting the IRQ routing. If userspace >> + * 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 :) Yes, the current code has some corner cases where a guest can shoot himself in the foot. This variant could actually be safer. > > [...] > >> static int kvm_s390_adapter_unmap(struct kvm *kvm, unsigned int id, __u64 addr) >> { >> - struct s390_io_adapter *adapter = get_io_adapter(kvm, id); >> - struct s390_map_info *map, *tmp; >> - int found = 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 == addr) { >> - found = 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? And do a return in the handler? maybe yes. Will have a look. > >> } > >> +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; >> >> if (!adapter) >> return NULL; >> - >> - list_for_each_entry(map, &adapter->maps, list) { >> - if (map->guest_addr == addr) >> - return map; >> - } >> - return NULL; >> + page = NULL; > > struct page *page = NULL; > >> + if (!uaddr) >> + return NULL; >> + down_read(&kvm->mm->mmap_sem); >> + ret = get_user_pages_remote(NULL, kvm->mm, uaddr, 1, FOLL_WRITE, >> + &page, NULL, NULL); >> + if (ret < 1) >> + page = 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. Probably. Will have a look.