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Mon, 15 Apr 2024 18:24:26 GMT Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2E1E42004D; Mon, 15 Apr 2024 18:24:24 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 027CD20040; Mon, 15 Apr 2024 18:24:23 +0000 (GMT) Received: from li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com (unknown [9.171.55.218]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTPS; Mon, 15 Apr 2024 18:24:22 +0000 (GMT) Date: Mon, 15 Apr 2024 20:24:21 +0200 From: Alexander Gordeev To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Andrew Morton , Peter Xu , Sven Schnelle , Gerald Schaefer , Andrea Arcangeli , kvm@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [PATCH v3 2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests Message-ID: References: <20240411161441.910170-1-david@redhat.com> <20240411161441.910170-3-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240411161441.910170-3-david@redhat.com> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 6GtmAc9B6K8dT-flaQntzbzZokvwdNLl X-Proofpoint-GUID: TdFM_63pvcjBbl31JkZc0XttxYHE-oxj X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-04-15_15,2024-04-15_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 clxscore=1015 priorityscore=1501 mlxscore=0 spamscore=0 suspectscore=0 phishscore=0 mlxlogscore=691 impostorscore=0 malwarescore=0 adultscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2404010000 definitions=main-2404150121 X-Stat-Signature: ddgu8q6gtnbu795nz8y7k8gr6cs6efbc X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C3051C000A X-Rspam-User: X-HE-Tag: 1713205472-926015 X-HE-Meta: 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 AI8fOrdi gsvisUd5WcofETL0V9PQjQENU6Jhjfx/xEuxemo6RzMs7M6N9gpPPBpXpsXqogM1fVs+WVOtlRaxv84OwxevXpksoaxoN55n8qtSUc7OEhMMWRzwVe69rzLcwYTlV0CZT8AMVPUe0vW/7KUVrFwjHpn2CkrgRFwva+ttHvxgB690kD8mb+M1YxqbNq1lQ1u62VM19nblqTUyJSTBJtN0QGL+W6ZyetzqpvbJ85jE0nuljrze+CDjTJ6CT4BXJSBoQINfpRrOc7b6rRkA= 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: List-Subscribe: List-Unsubscribe: On Thu, Apr 11, 2024 at 06:14:41PM +0200, David Hildenbrand wrote: David, could you please clarify the below questions? > +static int __s390_unshare_zeropages(struct mm_struct *mm) > +{ > + struct vm_area_struct *vma; > + VMA_ITERATOR(vmi, mm, 0); > + unsigned long addr; > + int rc; > + > + for_each_vma(vmi, vma) { > + /* > + * We could only look at COW mappings, but it's more future > + * proof to catch unexpected zeropages in other mappings and > + * fail. > + */ > + if ((vma->vm_flags & VM_PFNMAP) || is_vm_hugetlb_page(vma)) > + continue; > + addr = vma->vm_start; > + > +retry: > + rc = walk_page_range_vma(vma, addr, vma->vm_end, > + &find_zeropage_ops, &addr); > + if (rc <= 0) > + continue; So in case an error is returned for the last vma, __s390_unshare_zeropage() finishes with that error. By contrast, the error for a non-last vma would be ignored? > + > + /* addr was updated by find_zeropage_pte_entry() */ > + rc = handle_mm_fault(vma, addr, > + FAULT_FLAG_UNSHARE | FAULT_FLAG_REMOTE, > + NULL); > + if (rc & VM_FAULT_OOM) > + return -ENOMEM; Heiko pointed out that rc type is inconsistent vs vm_fault_t returned by handle_mm_fault(). While fixing it up, I've got concerned whether is it fine to continue in case any other error is met (including possible future VM_FAULT_xxxx)? > + /* > + * See break_ksm(): even after handle_mm_fault() returned 0, we > + * must start the lookup from the current address, because > + * handle_mm_fault() may back out if there's any difficulty. > + * > + * VM_FAULT_SIGBUS and VM_FAULT_SIGSEGV are unexpected but > + * maybe they could trigger in the future on concurrent > + * truncation. In that case, the shared zeropage would be gone > + * and we can simply retry and make progress. > + */ > + cond_resched(); > + goto retry; > + } > + > + return rc; > +} Thanks!