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Tue, 15 Oct 2024 16:43:30 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay01.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 49FGhRGY49545570 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 15 Oct 2024 16:43:27 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5D9BB20040; Tue, 15 Oct 2024 16:43:27 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 36DE620043; Tue, 15 Oct 2024 16:43:27 +0000 (GMT) Received: from p-imbrenda.boeblingen.de.ibm.com (unknown [9.152.224.66]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 15 Oct 2024 16:43:27 +0000 (GMT) From: Claudio Imbrenda To: linux-kernel@vger.kernel.org Cc: borntraeger@de.ibm.com, nsg@linux.ibm.com, nrb@linux.ibm.com, frankja@linux.ibm.com, seiden@linux.ibm.com, hca@linux.ibm.com, agordeev@linux.ibm.com, gor@linux.ibm.com, gerald.schaefer@linux.ibm.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org Subject: [PATCH v3 03/11] s390/mm/gmap: Refactor gmap_fault() and add support for pfault Date: Tue, 15 Oct 2024 18:43:18 +0200 Message-ID: <20241015164326.124987-4-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241015164326.124987-1-imbrenda@linux.ibm.com> References: <20241015164326.124987-1-imbrenda@linux.ibm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: GCnQJhRIBaJqnCV4V8nw9FXw21eE_aN6 X-Proofpoint-ORIG-GUID: GCnQJhRIBaJqnCV4V8nw9FXw21eE_aN6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-15_01,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 phishscore=0 clxscore=1015 malwarescore=0 suspectscore=0 lowpriorityscore=0 mlxlogscore=782 adultscore=0 mlxscore=0 priorityscore=1501 bulkscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2410150113 When specifying FAULT_FLAG_RETRY_NOWAIT as flag for gmap_fault(), the gmap fault will be processed only if it can be resolved quickly and without sleeping. This will be needed for pfault. Refactor gmap_fault() to improve readability. Signed-off-by: Claudio Imbrenda Acked-by: Alexander Gordeev --- arch/s390/mm/gmap.c | 119 +++++++++++++++++++++++++++++++++++++------- 1 file changed, 100 insertions(+), 19 deletions(-) diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c index eb0b51a36be0..f51ad948ba53 100644 --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c @@ -637,44 +637,125 @@ int __gmap_link(struct gmap *gmap, unsigned long gaddr, unsigned long vmaddr) } /** - * gmap_fault - resolve a fault on a guest address + * fixup_user_fault_nowait - manually resolve a user page fault without waiting + * @mm: mm_struct of target mm + * @address: user address + * @fault_flags:flags to pass down to handle_mm_fault() + * @unlocked: did we unlock the mmap_lock while retrying + * + * This function behaves similarly to fixup_user_fault(), but it guarantees + * that the fault will be resolved without waiting. The function might drop + * and re-acquire the mm lock, in which case @unlocked will be set to true. + * + * The guarantee is that the fault is handled without waiting, but the + * function itself might sleep, due to the lock. + * + * Context: Needs to be called with mm->mmap_lock held in read mode, and will + * return with the lock held in read mode; @unlocked will indicate whether + * the lock has been dropped and re-acquired. This is the same behaviour as + * fixup_user_fault(). + * + * Return: 0 on success, -EAGAIN if the fault cannot be resolved without + * waiting, -EFAULT if the fault cannot be resolved, -ENOMEM if out of + * memory. + */ +static int fixup_user_fault_nowait(struct mm_struct *mm, unsigned long address, + unsigned int fault_flags, bool *unlocked) +{ + struct vm_area_struct *vma; + unsigned int test_flags; + vm_fault_t fault; + int rc; + + fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT; + test_flags = fault_flags & FAULT_FLAG_WRITE ? VM_WRITE : VM_READ; + + vma = find_vma(mm, address); + if (unlikely(!vma || address < vma->vm_start)) + return -EFAULT; + if (unlikely(!(vma->vm_flags & test_flags))) + return -EFAULT; + + fault = handle_mm_fault(vma, address, fault_flags, NULL); + /* the mm lock has been dropped, take it again */ + if (fault & VM_FAULT_COMPLETED) { + *unlocked = true; + mmap_read_lock(mm); + return 0; + } + /* the mm lock has not been dropped */ + if (fault & VM_FAULT_ERROR) { + rc = vm_fault_to_errno(fault, 0); + BUG_ON(!rc); + return rc; + } + /* the mm lock has not been dropped because of FAULT_FLAG_RETRY_NOWAIT */ + if (fault & VM_FAULT_RETRY) + return -EAGAIN; + /* nothing needed to be done and the mm lock has not been dropped */ + return 0; +} + +/** + * __gmap_fault - resolve a fault on a guest address * @gmap: pointer to guest mapping meta data structure * @gaddr: guest address * @fault_flags: flags to pass down to handle_mm_fault() * - * Returns 0 on success, -ENOMEM for out of memory conditions, and -EFAULT - * if the vm address is already mapped to a different guest segment. + * Context: Needs to be called with mm->mmap_lock held in read mode. Might + * drop and re-acquire the lock. Will always return with the lock held. */ -int gmap_fault(struct gmap *gmap, unsigned long gaddr, - unsigned int fault_flags) +static int __gmap_fault(struct gmap *gmap, unsigned long gaddr, unsigned int fault_flags) { unsigned long vmaddr; - int rc; bool unlocked; - - mmap_read_lock(gmap->mm); + int rc = 0; retry: unlocked = false; + vmaddr = __gmap_translate(gmap, gaddr); - if (IS_ERR_VALUE(vmaddr)) { - rc = vmaddr; - goto out_up; - } - if (fixup_user_fault(gmap->mm, vmaddr, fault_flags, - &unlocked)) { - rc = -EFAULT; - goto out_up; + if (IS_ERR_VALUE(vmaddr)) + return vmaddr; + + if (fault_flags & FAULT_FLAG_RETRY_NOWAIT) { + rc = fixup_user_fault_nowait(gmap->mm, vmaddr, fault_flags, &unlocked); + if (rc) + return rc; + } else if (fixup_user_fault(gmap->mm, vmaddr, fault_flags, &unlocked)) { + return -EFAULT; } /* * In the case that fixup_user_fault unlocked the mmap_lock during - * faultin redo __gmap_translate to not race with a map/unmap_segment. + * fault-in, redo __gmap_translate() to avoid racing with a + * map/unmap_segment. + * In particular, __gmap_translate(), fixup_user_fault{,_nowait}(), + * and __gmap_link() must all be called atomically in one go; if the + * lock had been dropped in between, a retry is needed. */ if (unlocked) goto retry; - rc = __gmap_link(gmap, gaddr, vmaddr); -out_up: + return __gmap_link(gmap, gaddr, vmaddr); +} + +/** + * gmap_fault - resolve a fault on a guest address + * @gmap: pointer to guest mapping meta data structure + * @gaddr: guest address + * @fault_flags: flags to pass down to handle_mm_fault() + * + * Returns 0 on success, -ENOMEM for out of memory conditions, -EFAULT if the + * vm address is already mapped to a different guest segment, and -EAGAIN if + * FAULT_FLAG_RETRY_NOWAIT was specified and the fault could not be processed + * immediately. + */ +int gmap_fault(struct gmap *gmap, unsigned long gaddr, unsigned int fault_flags) +{ + int rc; + + mmap_read_lock(gmap->mm); + rc = __gmap_fault(gmap, gaddr, fault_flags); mmap_read_unlock(gmap->mm); return rc; }