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Tue, 20 Oct 2026 14:33:11 +0000 (GMT) Received: from b35lp69.lnxne.boe (unknown [9.87.84.240]) by smtpav02.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 20 Oct 2026 14:33:10 +0000 (GMT) From: Christian Borntraeger To: Janosch Frank , Claudio Imbrenda , Paolo Bonzini , Sean Christopherson Cc: KVM , Christian Borntraeger , linux-s390 , Shuah Khan Subject: [PATCH 1/2] KVM: Set up async page faults only for faults that need to wait Date: Tue, 20 Oct 2026 16:33:07 +0200 Message-ID: <20261020143308.228328-2-borntraeger@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261020143308.228328-1-borntraeger@linux.ibm.com> References: <20261020143308.228328-1-borntraeger@linux.ibm.com> X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYxMDIwMDA1NiBTYWx0ZWRfX+X8uS9nnYvgk 88Hc3HjxK2vFv46cdXNMtoczbmomOXbYQXJNtPW57uakRKoalQ4FOoKsrjypSbbDhZGYmbll0RQ y4jmaRY7yvAibdmwcfCwvMcsOnAOABM= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDIwMDA1NiBTYWx0ZWRfXxu0l6YUWbPOk ry7vkwJl9hZw9fKXGsYUHkd009vgUR4H8Tq4cEWaeVGQvrSl0OmQIMyJV7b4YVZJIoXgBbGsc3p DN/b8Adz9jdCcF1zsWjBZQPke7JXO/++t3R5kseSZCNfnPrX1PZZre4uKe4CNP4GF9AodUNxwNw waRnZqGhKqJzpRLeCevngY39LA7LXXnVKa52oDvH1tSDV7nW80TuWlyP4ZP67NYbJcfie1GImOL ZiWeigH5A99T4E/SD8bChVs6j/8kX/BccfYS16OauzkBemQDmoNoHFxRo9JVBMqWLUGXR6ZDxiA ZxHhtDG2zk3Qiwo3Fi2FrEkWrVdrfuBbPvhxzgJgcF3OyUce7ytgM8cngEKlq9ds5PDh1Zvp2Tw wsMhYlJ+Qlkk96JvNQ3WYnmOMYtLF/7dnZzVYzL56k0AiWBIzqZpM8k0V4dFk5ffZC++JhoRg7W DZ+0eaO9mp3cwn8WZZA== X-Proofpoint-GUID: Zvef_ByYTYQLBf8vihPeg0xd5GibJuWH X-Authority-Analysis: v=2.4 cv=JIKuIMKb c=1 sm=1 tr=0 ts=6ad77bab cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=2XfxGlgA2qNMPojl:21 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=B90Q0sit6v1lwuMtttgA:9 X-Proofpoint-ORIG-GUID: X8GrOVqDz2ryGb4OIS5AORN8rBnxMJ8E X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-10-20_02,2026-10-19_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 adultscore=0 priorityscore=1501 spamscore=0 phishscore=0 bulkscore=0 clxscore=1015 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610190000 definitions=main-2610200056 hva_to_pfn() checks a FOLL_NOWAIT gup() for EINTR, EAGAIN and EHWPOISON. There might be others like -EFAULT for VM_FAULT_SIGBUS. For those other errors, reporting KVM_PFN_ERR_NEEDS_IO would be wrong as it triggers an async_pf resulting in endless retries. Return KVM_PFN_ERR_NEEDS_IO only if gup() returned 0 pages and report the error otherwise. Fixes: 0857b9e95c1a ("KVM: Enable async page fault processing") Signed-off-by: Christian Borntraeger --- virt/kvm/kvm_main.c | 1 + 1 file changed, 1 insertion(+) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 5a782849521c..34b38d7512c3 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3048,6 +3048,7 @@ kvm_pfn_t hva_to_pfn(struct kvm_follow_pfn *kfp) pfn = KVM_PFN_ERR_FAULT; } else { if ((kfp->flags & FOLL_NOWAIT) && + npages == 0 && /* no PFN_ERR_NEEDS_IO on errors */ vma_is_valid(vma, kfp->flags & FOLL_WRITE)) pfn = KVM_PFN_ERR_NEEDS_IO; else -- 2.53.0