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Mon, 25 Aug 2025 07:58:56 +0000 (GMT) Message-ID: Date: Mon, 25 Aug 2025 09:58:56 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: s390: Fix access to unavailable adapter indicator pages during postcopy To: Thomas Huth , Claudio Imbrenda , kvm@vger.kernel.org Cc: Peter Xu , Christian Borntraeger , David Hildenbrand , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250821152309.847187-1-thuth@redhat.com> Content-Language: en-US From: Janosch Frank Autocrypt: addr=frankja@linux.ibm.com; keydata= xsFNBFubpD4BEADX0uhkRhkj2AVn7kI4IuPY3A8xKat0ihuPDXbynUC77mNox7yvK3X5QBO6 qLqYr+qrG3buymJJRD9xkp4mqgasHdB5WR9MhXWKH08EvtvAMkEJLnqxgbqf8td3pCQ2cEpv 15mH49iKSmlTcJ+PvJpGZcq/jE42u9/0YFHhozm8GfQdb9SOI/wBSsOqcXcLTUeAvbdqSBZe zuMRBivJQQI1esD9HuADmxdE7c4AeMlap9MvxvUtWk4ZJ/1Z3swMVCGzZb2Xg/9jZpLsyQzb lDbbTlEeyBACeED7DYLZI3d0SFKeJZ1SUyMmSOcr9zeSh4S4h4w8xgDDGmeDVygBQZa1HaoL Esb8Y4avOYIgYDhgkCh0nol7XQ5i/yKLtnNThubAcxNyryw1xSstnKlxPRoxtqTsxMAiSekk 0m3WJwvwd1s878HrQNK0orWd8BzzlSswzjNfQYLF466JOjHPWFOok9pzRs+ucrs6MUwDJj0S cITWU9Rxb04XyigY4XmZ8dywaxwi2ZVTEg+MD+sPmRrTw+5F+sU83cUstuymF3w1GmyofgsU Z+/ldjToHnq21MNa1wx0lCEipCCyE/8K9B9bg9pUwy5lfx7yORP3JuAUfCYb8DVSHWBPHKNj HTOLb2g2UT65AjZEQE95U2AY9iYm5usMqaWD39pAHfhC09/7NQARAQABzSVKYW5vc2NoIEZy YW5rIDxmcmFua2phQGxpbnV4LmlibS5jb20+wsF3BBMBCAAhBQJbm6Q+AhsjBQsJCAcCBhUI CQoLAgQWAgMBAh4BAheAAAoJEONU5rjiOLn4p9gQALjkdj5euJVI2nNT3/IAxAhQSmRhPEt0 AmnCYnuTcHRWPujNr5kqgtyER9+EMQ0ZkX44JU2q7OWxTdSNSAN/5Z7qmOR9JySvDOf4d3mS bMB5zxL9d8SbnSs1uW96H9ZBTlTQnmLfsiM9TetAjSrR8nUmjGhe2YUhJLR1v1LguME+YseT eXnLzIzqqpu311/eYiiIGcmaOjPCE+vFjcXL5oLnGUE73qSYiujwhfPCCUK0850o1fUAYq5p CNBCoKT4OddZR+0itKc/cT6NwEDwdokeg0+rAhxb4Rv5oFO70lziBplEjOxu3dqgIKbHbjza EXTb+mr7VI9O4tTdqrwJo2q9zLqqOfDBi7NDvZFLzaCewhbdEpDYVu6/WxprAY94hY3F4trT rQMHJKQENtF6ZTQc9fcT5I3gAmP+OEvDE5hcTALpWm6Z6SzxO7gEYCnF+qGXqp8sJVrweMub UscyLqHoqdZC2UG4LQ1OJ97nzDpIRe0g6oJ9ZIYHKmfw5jjwH6rASTld5MFWajWdNsqK15k/ RZnHAGICKVIBOBsq26m4EsBlfCdt3b/6emuBjUXR1pyjHMz2awWzCq6/6OWs5eANZ0sdosNq dq2v0ULYTazJz2rlCXV89qRa7ukkNwdBSZNEwsD4eEMicj1LSrqWDZMAALw50L4jxaMD7lPL jJbazsFNBFubpD4BEADAcUTRqXF/aY53OSH7IwIK9lFKxIm0IoFkOEh7LMfp7FGzaP7ANrZd cIzhZi38xyOkcaFY+npGEWvko7rlIAn0JpBO4x3hfhmhBD/WSY8LQIFQNNjEm3vzrMo7b9Jb JAqQxfbURY3Dql3GUzeWTG9uaJ00u+EEPlY8zcVShDltIl5PLih20e8xgTnNzx5c110lQSu0 iZv2lAE6DM+2bJQTsMSYiwKlwTuv9LI9Chnoo6+tsN55NqyMxYqJgElk3VzlTXSr3+rtSCwf tq2cinETbzxc1XuhIX6pu/aCGnNfuEkM34b7G1D6CPzDMqokNFbyoO6DQ1+fW6c5gctXg/lZ 602iEl4C4rgcr3+EpfoPUWzKeM8JXv5Kpq4YDxhvbitr8Dm8gr38+UKFZKlWLlwhQ56r/zAU v6LIsm11GmFs2/cmgD1bqBTNHHcTWwWtRTLgmnqJbVisMJuYJt4KNPqphTWsPY8SEtbufIlY HXOJ2lqUzOReTrie2u0qcSvGAbSfec9apTFl2Xko/ddqPcZMpKhBiXmY8tJzSPk3+G4tqur4 6TYAm5ouitJsgAR61Cu7s+PNuq/pTLDhK+6/Njmc94NGBcRA4qTuysEGE79vYWP2oIAU4Fv6 gqaWHZ4MEI2XTqH8wiwzPdCQPYsSE0fXWiYu7ObeErT6iLSTZGx4rQARAQABwsFfBBgBCAAJ BQJbm6Q+AhsMAAoJEONU5rjiOLn4DDEP/RuyckW65SZcPG4cMfNgWxZF8rVjeVl/9PBfy01K 8R0hajU40bWtXSMiby7j0/dMjz99jN6L+AJHJvrLz4qYRzn2Ys843W+RfXj62Zde4YNBE5SL jJweRCbMWKaJLj6499fctxTyeb9+AMLQS4yRSwHuAZLmAb5AyCW1gBcTWZb8ON5BmWnRqeGm IgC1EvCnHy++aBnHTn0m+zV89BhTLTUal35tcjUFwluBY39R2ux/HNlBO1GY3Z+WYXhBvq7q katThLjaQSmnOrMhzqYmdShP1leFTVbzXUUIYv/GbynO/YrL2gaQpaP1bEUEi8lUAfXJbEWG dnHFkciryi092E8/9j89DJg4mmZqOau7TtUxjRMlBcIliXkzSLUk+QvD4LK1kWievJse4mte FBdkWHfP4BH/+8DxapRcG1UAheSnSRQ5LiO50annOB7oXF+vgKIaie2TBfZxQNGAs3RQ+bga DchCqFm5adiSP5+OT4NjkKUeGpBe/aRyQSle/RropTgCi85pje/juYEn2P9UAgkfBJrOHvQ9 Z+2Sva8FRd61NJLkCJ4LFumRn9wQlX2icFbi8UDV3do0hXJRRYTWCxrHscMhkrFWLhYiPF4i phX7UNdOWBQ90qpHyAxHmDazdo27gEjfvsgYMdveKknEOTEb5phwxWgg7BcIDoJf9UMC In-Reply-To: <20250821152309.847187-1-thuth@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: d3_Sz99F3zTh9VJAhpUpbZjJiwTa6YWR X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODIzMDAyMSBTYWx0ZWRfX3urjkaXzKH/a ijwfMZtgEm+EVN/Om7jBPITedQ1syhFS79QSzIdvaaLtZS9eanJwtMT/vh7+1H/QvY+gIeIa0ij pptOBu4XiEsYAfAnfmWWfF/vzoNyMKRoJxh7zqo9wG75Fz7rFvJ5H1vULXTg+Up7qLLn4Na2cSn ZPHxSllZWPWYjRN5MClj+pyXK5oK0KcTmKSKQo1JuVmG+U1OWEfAowcr3DHZwnQreYXsXhhIrAu PuldRpeYYSB/d/3uK+gNfHjS1jWMKMX42RMwk3WmnyCDUGyZGznLPscreAhpbZTNvTuSD4lnevm caLbHGH7BpvSlTZdS8AjStgTX9yb1S1ESCtiroU3+ZxlmnW/CqVUDt8o345iCLEZdxRwPp6Nt+u wEwJZWO7 X-Proofpoint-ORIG-GUID: d3_Sz99F3zTh9VJAhpUpbZjJiwTa6YWR X-Authority-Analysis: v=2.4 cv=SNNCVPvH c=1 sm=1 tr=0 ts=68ac17c6 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=2OwXVqhp2XgA:10 a=20KFwNOVAAAA:8 a=VnNF1IyMAAAA:8 a=btW-XHHgg9hxShBi8oQA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-25_03,2025-08-20_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 adultscore=0 bulkscore=0 phishscore=0 clxscore=1015 impostorscore=0 malwarescore=0 suspectscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2508230021 On 8/21/25 5:23 PM, Thomas Huth wrote: > From: Thomas Huth > > When you run a KVM guest with vhost-net and migrate that guest to > another host, and you immediately enable postcopy after starting the > migration, there is a big chance that the network connection of the > guest won't work anymore on the destination side after the migration. > > With a debug kernel v6.16.0, there is also a call trace that looks > like this: > > FAULT_FLAG_ALLOW_RETRY missing 881 > CPU: 6 UID: 0 PID: 549 Comm: kworker/6:2 Kdump: loaded Not tainted 6.16.0 #56 NONE > Hardware name: IBM 3931 LA1 400 (LPAR) > Workqueue: events irqfd_inject [kvm] > Call Trace: > [<00003173cbecc634>] dump_stack_lvl+0x104/0x168 > [<00003173cca69588>] handle_userfault+0xde8/0x1310 > [<00003173cc756f0c>] handle_pte_fault+0x4fc/0x760 > [<00003173cc759212>] __handle_mm_fault+0x452/0xa00 > [<00003173cc7599ba>] handle_mm_fault+0x1fa/0x6a0 > [<00003173cc73409a>] __get_user_pages+0x4aa/0xba0 > [<00003173cc7349e8>] get_user_pages_remote+0x258/0x770 > [<000031734be6f052>] get_map_page+0xe2/0x190 [kvm] > [<000031734be6f910>] adapter_indicators_set+0x50/0x4a0 [kvm] > [<000031734be7f674>] set_adapter_int+0xc4/0x170 [kvm] > [<000031734be2f268>] kvm_set_irq+0x228/0x3f0 [kvm] > [<000031734be27000>] irqfd_inject+0xd0/0x150 [kvm] > [<00003173cc00c9ec>] process_one_work+0x87c/0x1490 > [<00003173cc00dda6>] worker_thread+0x7a6/0x1010 > [<00003173cc02dc36>] kthread+0x3b6/0x710 > [<00003173cbed2f0c>] __ret_from_fork+0xdc/0x7f0 > [<00003173cdd737ca>] ret_from_fork+0xa/0x30 > 3 locks held by kworker/6:2/549: > #0: 00000000800bc958 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x7ee/0x1490 > #1: 000030f3d527fbd0 ((work_completion)(&irqfd->inject)){+.+.}-{0:0}, at: process_one_work+0x81c/0x1490 > #2: 00000000f99862b0 (&mm->mmap_lock){++++}-{3:3}, at: get_map_page+0xa8/0x190 [kvm] > > The "FAULT_FLAG_ALLOW_RETRY missing" indicates that handle_userfaultfd() > saw a page fault request without ALLOW_RETRY flag set, hence userfaultfd > cannot remotely resolve it (because the caller was asking for an immediate > resolution, aka, FAULT_FLAG_NOWAIT, while remote faults can take time). > With that, get_map_page() failed and the irq was lost. > > We should not be strictly in an atomic environment here and the worker > should be sleepable (the call is done during an ioctl from userspace), > so we can allow adapter_indicators_set() to just sleep waiting for the > remote fault instead. > > Link: https://issues.redhat.com/browse/RHEL-42486 > Signed-off-by: Peter Xu > [thuth: Assembled patch description and fixed some cosmetical issues] > Signed-off-by: Thomas Huth Acked-by: Janosch Frank