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Tue, 20 Oct 2026 17:58:21 +0000 (GMT) Received: from b35lp69.lnxne.boe (unknown [9.87.84.240]) by smtpav03.wdc07v.mail.ibm.com (Postfix) with ESMTP; Tue, 20 Oct 2026 17:58:21 +0000 (GMT) From: Christian Borntraeger To: Janosch Frank , Claudio Imbrenda , Paolo Bonzini , Sean Christopherson Cc: KVM , Christian Borntraeger , linux-s390 , Shuah Khan Subject: [PATCH v2 1/2] KVM: Set up async page faults only for faults that need to wait Date: Tue, 20 Oct 2026 19:58:17 +0200 Message-ID: <20261020175818.375700-2-borntraeger@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261020175818.375700-1-borntraeger@linux.ibm.com> References: <20261020175818.375700-1-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: AW1haW4tMjYxMDIwMDA3MCBTYWx0ZWRfXzV9/ly0SYw1i 6v2P4Dh6nO9ygeijdIVEhBB8QpCbb2zPIzx1mGABIrJJts7RcRW5DnqJV/V0r1ebcikBeIQZtT0 bxVw8cHjzXJtxsALkfnh71Vg6htDB1Q= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDIwMDA3MCBTYWx0ZWRfX+bWHzzB7kXxw GtzrnB3aXo5/kn8a/ztIFxo2ZpKrfsUQDQXeUEOCdbFboZYOqYB3PS/2aRJ4tVCmW6IufTLex5b sQZrcEhHisuviEe3auZcqnaQdbBXM03lQNCYeoBuK9nPAqOJOKxn0X2+V6/YqzGi5H98YcpHXAN r+WfI4TM2Q1MkYPCBj8uvr9s50Zj1mEo8wuv54rs1mBui+InVoZr+JOTtkKE27gUnr7MClY6FHF iS8E6BffzPr4qGcu7O8eHRXqan8vBLQIsAh9O6db4mp7zVR0rol2/P4MUtIHCfmMV8SVv7m6h6j ShdT6R5SWCiLkI9DAOOr26O0Uf25R2Ym1Cn4dmhIx1xDG7KkGxylU+fWo97LeOY7gdHE7sVmppU bAWF65HwR6BqBMeC+v95D0wSHgmJJtgab5YItrzS4fesP7Sn3Eea/ElyXFv9E5T4ax47GufOdEX 2YnvASu1+EltGPUToTQ== X-Proofpoint-GUID: NwBRdd5XS66tUQf5osIxtN90FvZtenQj X-Authority-Analysis: v=2.4 cv=JIKuIMKb c=1 sm=1 tr=0 ts=6ad7abc1 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=2XfxGlgA2qNMPojl:21 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=XG9Rsx7q7O2Eji3_kFcA:9 X-Proofpoint-ORIG-GUID: fyfjvdF7YRFD7zhDK42dc_t4E0fT4cBg 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_03,2026-10-19_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-2610200070 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 | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 5a782849521c..7b6172810f34 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3047,7 +3047,8 @@ kvm_pfn_t hva_to_pfn(struct kvm_follow_pfn *kfp) if (r < 0) pfn = KVM_PFN_ERR_FAULT; } else { - if ((kfp->flags & FOLL_NOWAIT) && + /* Note, GUP returns '0' if retry is needed. */ + if (!npages && (kfp->flags & FOLL_NOWAIT) && vma_is_valid(vma, kfp->flags & FOLL_WRITE)) pfn = KVM_PFN_ERR_NEEDS_IO; else -- 2.53.0