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Wed, 22 Jul 2026 15:51:20 +0000 (GMT) Received: from [9.61.177.4] (unknown [9.61.177.4]) by smtpav06.wdc07v.mail.ibm.com (Postfix) with ESMTP; Wed, 22 Jul 2026 15:51:20 +0000 (GMT) Message-ID: <1f64ec8b-2e22-42c7-b823-74d2bc30f3aa@linux.ibm.com> Date: Wed, 22 Jul 2026 11:51:19 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] KVM: s390: Fall back to short-term pinning in MAP ioctl To: Jaehoon Kim , borntraeger@linux.ibm.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com Cc: david@kernel.org, svens@linux.ibm.com, freimuth@linux.ibm.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260720222238.1576-1-jhkim@linux.ibm.com> From: Matthew Rosato Content-Language: en-US In-Reply-To: <20260720222238.1576-1-jhkim@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: R3xbM5RIPeq4mNg6fGus8t10C5cFyS4L X-Authority-Analysis: v=2.4 cv=V6RNF+ni c=1 sm=1 tr=0 ts=6a60e6fc cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=LBtEKoR7VHDbdQP3JW4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzIyMDE1NCBTYWx0ZWRfX+HDqYSUUHbOL iPvVUsqBFUsfCHXYIIL1tZhLeL6UCu2dovHLfVcgJaPYdyYZmqkMnSfa4Sln6MowJkN1np1w7NB SIkwGy/VnPLhdNQhow4036lA0M4byp8= X-Proofpoint-GUID: R3xbM5RIPeq4mNg6fGus8t10C5cFyS4L X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzIyMDE1NCBTYWx0ZWRfX2XTREPKad3o2 a1hbg2Lp7xT3oiltVwKWiNpN8gcBrAq/OXgKzAhELr0L5QDJRzglslyGJ5dhR3Ds4lkt2ECY7Y0 VOHJ2b0NRkGcsSfVsKo5+naTC+4XHbGgQZFDQfCmfzIrXLWLjGe68qo3YfnMCulBHyVB2BdwxRV FVsShHsggY4RjucQtC7LTQzHSMS/Y4eh9hKmAnWg7JXy/lZ5WDAnogQDpjEnRcxvR1R/e7ej4FJ yoeaSOx4yN5UXmlw0FOSuW9sYrUpv1vwMvwqod/vHtF5wA3zjxxSYQaGtDugDsd/qTWwTJaoyIk D4ywiF8QeSzm2nlxCwXvo7r4RWrrSYf7fbDxk1sPUPaS2MJeVzj9FjrlTfz/E3we3brKgTwn0Ms Tido7P0EKZLkWpiaOiuIj/S77v3Q+IXWHwtUjZH/gl2mF3InlzbxbwHM8axxjFIPvKuF6AgMGWR 5QxuUpqRQBS1Eq/s8rA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-22_04,2026-07-22_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 bulkscore=0 lowpriorityscore=0 clxscore=1015 spamscore=0 impostorscore=0 phishscore=0 priorityscore=1501 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607220154 On 7/20/26 6:22 PM, Jaehoon Kim wrote: > FOLL_LONGTERM pinning fails for some memory types, such as file-backed > guest memory. As a result, kvm_s390_adapter_map() returns -EINVAL and > irqfd adapter registration fails even though interrupt delivery could > still work via the existing non-atomic path. > > When FOLL_LONGTERM pinning fails, verify that the page is accessible > using a short-term pin instead. If the short-term pin succeeds, > immediately unpin the page and return success. The non-atomic irqfd > path already performs short-term pinning for interrupt delivery, so > this restores the previous behavior for memory that cannot be pinned > long-term. > > Fixes: adcd5b3e758b ("KVM: s390: Add map/unmap ioctl and clean mappings post-guest") > Signed-off-by: Jaehoon Kim > --- > arch/s390/kvm/interrupt.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index 9e3e6b0d72ad..4b68e0cb51f6 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -2520,8 +2520,19 @@ static int kvm_s390_adapter_map(struct kvm *kvm, unsigned int id, __u64 addr) > map->addr = host_addr; > map->page = pin_map_page(kvm, host_addr, FOLL_LONGTERM); > if (!map->page) { > - ret = -EINVAL; > - goto out; > + /* > + * Long-term pinning may fail for memory types such as file-backed > + * memory. Check whether short-term pinning is possible so that the > + * non-atomic irqfd path can handle interrupt injection. > + */ > + map->page = pin_map_page(kvm, host_addr, 0); > + if (!map->page) { > + ret = -EINVAL; > + goto out; > + } > + unpin_user_page(map->page); > + kfree(map); > + return 0; This makes sense, but what happens later on the kvm_s390_adapter_unmap? Won't we return -ENOENT because nothing was in the list? Is it worth detecting/recognizing this case? I could think of 2 ways... 1) re-doing the above test during unmap 2) stashing an entry in adapter->maps but with a new flag that indicates it was approved for short-term pinning only (e.g. return NULL immediately if a match is found during get_map_info() with this flag set), and during kvm_s390_adapter_unmap() and kvm_s390_unmap_all_adapters() just remove it from the list without doing any unpin/page dirtying. #2 might be a little more code but sounds cleaner?