From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D31FC2BEFE8; Thu, 13 Aug 2026 17:58:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.156.1 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786643940; cv=none; b=I0DtFmTzogxcSJI0ytvWyLE382BJ2ZgZKYJNEzf8txBBazBUcr6SSsjRieSRtg+K8j2uCvGMeQ0u1IdhVxiyCvLJHnLJTqDabEYlm7b+3+bAvGP9CxYgsC5LAuKfw0HAlPtOOXZPpGT0kmqePXCE+VpLWvRyl8BUw0wwsmL+U88= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786643940; c=relaxed/simple; bh=bdk3csiV7sVC+OjawUYp9wtf/SKvhKbV6zpy8Jh2v3s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fmLHChMgKtfXMcYjddj6ICzJTl+0F1pLGVpK4IPmP7cOxia9dronbzP7w7FnlclodP/IulLywpSnkc3d+8Tpf52qwQXD4qSCc83fk4QpeIHFVLco85GoMnLb9WMJsyzNfcPAFa5FtfjsM2rqSACadKCYACE3SiT868bQn7D+8rE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=na1LApIS; arc=none smtp.client-ip=148.163.156.1 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="na1LApIS" Received: from pps.filterd (m0356517.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 67DFWxXr2737435; Thu, 13 Aug 2026 17:58:41 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=sEpFR8 Dz4zPLitU7CrouNAB0RyuVXz+cyk0t/3+1le0=; b=na1LApISzh/UgsLWI8eIKe qSRNyEFXIeyFPPtjVIPYt0+ixNixfn+2z+C8WSGwIpTN4zKu12EsP/x2ndZbVuEi 6xgG2ZAl/MQ691q5IrI+s8Z02MksGSLOyILZjnDZzAG/BQPzVgM+OlGVzJNTCTjx iF3pBaj+n13MwRZt5Vcd2uqmZOZ6m7OY1T9NhOaawftKytwKvwspu8hcSYjb4zFN ngSDBfbJgJmX6lJog1D1pz7MGG5Kb3oc04Lygtm6y4EYsyIaBeuZdjoSWpGs/wYg ndNPlvt2aF6RkODVSSHx/hnM8TQDmHQVdsMrqs/SKH+leWZOuV+urW/xqSVeigDw == Received: from ppma12.dal12v.mail.ibm.com (dc.9e.1632.ip4.static.sl-reverse.com [50.22.158.220]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4fwvma1afk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Aug 2026 17:58:40 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 67DHuH8M030797; Thu, 13 Aug 2026 17:58:39 GMT Received: from smtprelay05.wdc07v.mail.ibm.com ([172.16.1.72]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 4fxesqc7mb-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Aug 2026 17:58:39 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (smtpav05.dal12v.mail.ibm.com [10.241.53.104]) by smtprelay05.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 67DHwb7230999046 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 13 Aug 2026 17:58:38 GMT Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CB5E158056; Thu, 13 Aug 2026 17:58:37 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B6B1658052; Thu, 13 Aug 2026 17:58:36 +0000 (GMT) Received: from [9.61.3.203] (unknown [9.61.3.203]) by smtpav05.dal12v.mail.ibm.com (Postfix) with ESMTP; Thu, 13 Aug 2026 17:58:36 +0000 (GMT) Message-ID: <9c69c913-49aa-4934-b46a-1ebddd425f76@linux.ibm.com> Date: Thu, 13 Aug 2026 11:08:58 -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 v7 07/15] s390/vfio-ap: File ops called to save the vfio device migration state To: Anthony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: borntraeger@de.ibm.com, mjrosato@linux.ibm.com, pasic@linux.ibm.com, alex@shazbot.org, kwankhede@nvidia.com, fiuczy@linux.ibm.com, pbonzini@redhat.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, agordeev@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com References: <20260807221834.562851-1-akrowiak@linux.ibm.com> <20260807221834.562851-8-akrowiak@linux.ibm.com> Content-Language: en-US From: "Jason J. Herne" In-Reply-To: <20260807221834.562851-8-akrowiak@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODEzMDEyNiBTYWx0ZWRfX6uwg2FFBAuBm G08KrAMqgaJBi0prfz+XEY+tqZxRc/InSh+yjYuYrSRP10hRCzHW6jG59VsrxNjO7zUbTnpuTcP GxIOLwUYzHgymNljUSg6yfwq2u98XG+A/XPo5UnyXMfTadK1nwRYOZMAZYW/DF/TNDqIjn0iNw0 JzRjNev5V69E8TfKGNOhimj12CseAWlr0PUGjCeMDvRCUxygsPbPexs8cYOSQpoWU1a7t+gEuzn qJB/bqVZVamv9pXa/Yfz/7epkkMkmAhHZ1+yvnIWxaLFlPYJdtoJ+J2R1fR7L2x9iV1NEr7ScmN uha3rMZGO8sTB3zuLtVpHPWdLQ5Lp0DmBeYLAijk8v5zEd4jcnCfzKsJBamWEJFVQmZna7K7Xgh 0DUhmH0XeHjnn5AKrd3QIB65QNxD716DR1VgSqZ0raWYgG7RUs+pO1YHXGx6v2lPwzKRIEcUifu qN829t6ceK6jCSzoIPg== X-Proofpoint-ORIG-GUID: hlyOeglxGJjOYADTcbI20OSR0F6_9rC_ X-Proofpoint-Spam-Info: AW1haW4tMjYwODEzMDEyNiBTYWx0ZWRfX7nvkBGXOPZhv wXXUmJB87cl2VzaT2t1h6VShrrHatdw7NkmxenK7384si73b3qIyX7Oh66ajvTkgvGjJY9sLedy DEDmpy+1Usjyi3O/HhDxb2c6Sapn5rs= X-Authority-Analysis: v=2.4 cv=IfK3n2qa c=1 sm=1 tr=0 ts=6a7e05d0 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=MMOTJcf4fHmcpOg2hCkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: hlyOeglxGJjOYADTcbI20OSR0F6_9rC_ 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=2026-08-13_05,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 impostorscore=0 bulkscore=0 clxscore=1015 lowpriorityscore=0 adultscore=0 malwarescore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608130126 On 8/7/26 6:18 PM, Anthony Krowiak wrote: > Implements the read callback function that was added to the > file_operations structure for the file created to save the state of the > vfio-ap device when the migration state transitioned from STOP to > to the STOP_COPY state. > > This function copies the guest's AP configuration information to > userspace. The information copied is comprised of the APQN of each queue > device passed through to the guest along with its hardware information. > This state data will be transferred to the vfio_ap device driver on the > destination host when the state is transitioned to RESUMING. > > Signed-off-by: Anthony Krowiak > --- > drivers/s390/crypto/vfio_ap_migration.c | 287 +++++++++++++++++++++++- > 1 file changed, 277 insertions(+), 10 deletions(-) > > diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c > index de693b308925..50781b61f7f1 100644 > --- a/drivers/s390/crypto/vfio_ap_migration.c > +++ b/drivers/s390/crypto/vfio_ap_migration.c > @@ -117,9 +117,10 @@ struct vfio_ap_config { > static void > vfio_ap_release_stop_copy_file(struct vfio_ap_migration_data *mig_data) > { > - /* Stub to be implemented when the mig_data->stop_copy_mig_file.ap_config > - * object is allocated. > - */ > + kvfree(mig_data->stop_copy_mig_file.ap_config); > + mig_data->stop_copy_mig_file.ap_config = NULL; > + mig_data->stop_copy_mig_file.config_sz = 0; > + mig_data->stop_copy_mig_file.filp = NULL; > } > > static void vfio_ap_release_resuming_file(struct vfio_ap_migration_data *mig_data) > @@ -129,13 +130,6 @@ static void vfio_ap_release_resuming_file(struct vfio_ap_migration_data *mig_dat > */ > } > > -static ssize_t > -vfio_ap_stop_copy_read(struct file *, char __user *, size_t, loff_t *) > -{ > - /* TODO */ > - return -EOPNOTSUPP; > -} > - > static int vfio_ap_release_mig_file(struct inode *file_inode, struct file *filp) > { > struct ap_matrix_mdev *matrix_mdev = filp->private_data; > @@ -150,6 +144,279 @@ static int vfio_ap_release_mig_file(struct inode *file_inode, struct file *filp) > return 0; > } > > +/** > + * validate_stop_copy_read_parms: Validate the input parameters to the > + * vfio_ap_stop_copy_read function > + * > + * @matrix_mdev: The object device containing the state to be read > + * @filp: Pointer to the file stream used to read the vfio-ap device state > + * @pos: The file offset from which to start reading data > + * @len: The length of the data to be read > + * > + * Verify the following: > + * - @filp private data is an ap_matrix_mdev instance > + * - @filp is the instance opened when state transitioned from STOP to STOP_COPY > + * - @pos + @len does not cause integer overflow > + * > + * Returns: 0 if the parameters pass validation; otherwise returns an error > + */ > +static int validate_stop_copy_read_parms(struct file *filp, loff_t *pos, > + size_t len) > +{ > + struct vfio_ap_migration_data *mig_data; > + struct ap_matrix_mdev *matrix_mdev; > + loff_t total_len; > + > + lockdep_assert_held(&matrix_dev->mdevs_lock); > + > + if (check_add_overflow((loff_t)len, *pos, &total_len)) > + return -EIO; > + > + /* > + * matrix_mdev is guaranteed live here: vfio_ap_open_file_stream() took > + * a vfio_device registration reference that is held until > + * vfio_ap_release_mig_file() runs, so the embedding matrix_mdev cannot > + * be freed while this file descriptor is open. > + */ > + matrix_mdev = filp->private_data; > + > + if (!matrix_mdev->mig_data) > + return -ENODEV; > + > + mig_data = matrix_mdev->mig_data; > + > + if (mig_data->stop_copy_mig_file.filp != filp) > + return -EINVAL; > + > + return 0; > +} > + > +static size_t vfio_ap_config_size(struct ap_matrix_mdev *matrix_mdev, > + int *num_queues) > +{ > + size_t qinfo_size; > + > + lockdep_assert_held(&matrix_dev->mdevs_lock); > + > + *num_queues = vfio_ap_mdev_get_num_queues(&matrix_mdev->shadow_apcb); > + qinfo_size = *num_queues * sizeof(struct vfio_ap_queue_info); > + > + return qinfo_size + sizeof(struct vfio_ap_config); > +} > + > +static int get_hardware_info_for_queue(const char *mdev_name, > + struct ap_tapq_hwinfo *hwinfo, > + unsigned long apqn) > +{ > + struct ap_queue_status status; > + > + status = ap_tapq(apqn, hwinfo); > + > + switch (status.response_code) { > + case AP_RESPONSE_NORMAL: > + case AP_RESPONSE_RESET_IN_PROGRESS: > + case AP_RESPONSE_DECONFIGURED: > + case AP_RESPONSE_CHECKSTOPPED: > + case AP_RESPONSE_BUSY: > + /* For all these RCs the tapq info should be available */ > + return 0; > + case AP_RESPONSE_Q_NOT_AVAIL: > + pr_err_ratelimited("vfio_ap_mdev %s: Failed to get hwinfo for queue %02lx.%04lx: TAPQ rc=%d", > + mdev_name, AP_QID_CARD(apqn), AP_QID_QUEUE(apqn), > + status.response_code); > + return -ENODEV; > + default: > + /* > + * Without a pending async error, the tapq info should be > + * available > + */ > + if (status.async) > + return 0; > + > + pr_err_ratelimited("vfio_ap_mdev %s:Failed to get hwinfo for queue %02lx.%04lx: TAPQ rc=%d", > + mdev_name, AP_QID_CARD(apqn), AP_QID_QUEUE(apqn), > + status.response_code); > + return -EIO; > + } > +} > + > +/** > + * vfio_ap_store_queue_info: > + * > + * Stores the hardware information returned from the PQAP(TAPQ) command for each > + * queue device identified in the 'qinfo' field of the a vfio_ap_config > + * object. If there are a large number of queues for which hardware information > + * must be retrieved, this function must be called without the mdevs_lock > + * held. This should not be a problem since the APQNs in the 'qinfo' field > + * should already have been snapshotted prior to calling this function. This warning message is ambiguous. What does large mean? What are the consequences of holding the lock during a long call? And, "This should not be a problem..." this whole thing seems to contradict the warning entirely. Can you clarify the situation? :) > + * > + * @mdev_name: The name (UUID) of the mediated device to use in log messages > + * @ap_config: A reference to the vfio_ap_config instance in which to store > + * the queue information. It is expected that each APQN identifying > + * a queue device for which hardware information is to be retrieved > + * shall be snapshotted prior to calling this function. > + * > + * Returns: Zero (0) if the hardware information is retrieved for each queue > + * device in the AP configuration; otherwise, returns an error. > + */ > +static int vfio_ap_store_queue_info(const char *mdev_name, > + struct vfio_ap_config *ap_config) > +{ > + struct ap_tapq_hwinfo source_hwinfo; > + unsigned long num_queues; > + int ret; > + > + for (num_queues = 0; num_queues < ap_config->num_queues; num_queues++) { > + ret = get_hardware_info_for_queue(mdev_name, &source_hwinfo, > + ap_config->qinfo[num_queues].apqn); > + if (ret) > + return ret; > + > + ap_config->qinfo[num_queues].data = source_hwinfo.value; > + } > + > + return 0; > +} > + > +static int vfio_ap_get_config(struct ap_matrix_mdev *matrix_mdev) > +{ > + struct vfio_ap_config *ap_configuration; > + unsigned long *apm, *aqm, apid, apqi; > + const char *mdev_name; > + size_t ap_config_size; > + int ret, num_queues; > + > + lockdep_assert_held(&matrix_dev->mdevs_lock); > + > + ap_config_size = vfio_ap_config_size(matrix_mdev, (int *)&num_queues); > + > + ap_configuration = kvzalloc(ap_config_size, GFP_KERNEL_ACCOUNT); > + if (!ap_configuration) > + return -ENOMEM; > + > + ap_configuration->magic = VFIO_AP_MIG_MAGIC; > + ap_configuration->version = VFIO_AP_MIG_VERSION; > + > + /* > + * num_queues must be set before writing qinfo[] elements; the > + * __counted_by(num_queues) annotation on qinfo[] causes the compiler to > + * insert bounds checks that evaluate against ap_configuration->num_queues. > + * Writing through qinfo[i] with num_queues still 0 would trap. > + */ > + ap_configuration->num_queues = num_queues; > + > + apm = matrix_mdev->shadow_apcb.apm; > + aqm = matrix_mdev->shadow_apcb.aqm; > + num_queues = 0; > + for_each_set_bit_inv(apid, apm, AP_DEVICES) { > + for_each_set_bit_inv(apqi, aqm, AP_DOMAINS) { > + ap_configuration->qinfo[num_queues].apqn = > + AP_MKQID(apid, apqi); > + num_queues += 1; > + } > + } > + memcpy(ap_configuration->adm, matrix_mdev->shadow_apcb.adm, > + sizeof(ap_configuration->adm)); > + mdev_name = dev_name(matrix_mdev->vdev.dev); > + > + /* > + * Unlock the mdevs_lock so other mdevs are not precluded from being > + * accessed while a potentially long running operation is performed. > + */ > + mutex_unlock(&matrix_dev->mdevs_lock); > + ret = vfio_ap_store_queue_info(mdev_name, ap_configuration); > + mutex_lock(&matrix_dev->mdevs_lock); I'm confused by the locking strategy here. Why is it okay to release the lock, do stuff, then reacquire the lock? If that's okay, why do we need the lock at all? What changes are we protecting against? And can those changes land when we relase the lock to call vfio_ap_store_queue_info()? > + if (ret) { > + kvfree(ap_configuration); > + return ret; > + } > + > + if (!matrix_mdev->mig_data) { > + kvfree(ap_configuration); > + return -ENODEV; > + } > + > + matrix_mdev->mig_data->stop_copy_mig_file.ap_config = ap_configuration; > + matrix_mdev->mig_data->stop_copy_mig_file.config_sz = ap_config_size; > + > + return 0; > +} > + > +static ssize_t vfio_ap_stop_copy_read(struct file *filp, char __user *buf, > + size_t len, loff_t *pos) > +{ > + struct vfio_ap_migration_file *mig_file; > + struct ap_matrix_mdev *matrix_mdev; > + loff_t read_pos; > + ssize_t ret; > + > + /* > + * This file was opened with stream_open(), so pos should be NULL for > + * sequential read() calls; a non-NULL pointer will be passed only > + * for positional pread() calls in which case we return an error > + * indicating broken pipe/illegal seek on a non-seekable file > + */ > + if (pos) > + return -ESPIPE; > + > + mutex_lock(&matrix_dev->mdevs_lock); > + > + pos = &filp->f_pos; > + > + ret = validate_stop_copy_read_parms(filp, pos, len); Why pass pos here? Can't validate_stop_copy_read_parms() just read it from fipl->f_pos? > + if (ret) { > + mutex_unlock(&matrix_dev->mdevs_lock); > + return ret; > + } > + > + matrix_mdev = filp->private_data; > + mig_file = &matrix_mdev->mig_data->stop_copy_mig_file; > + > + if (!mig_file->ap_config) { > + ret = vfio_ap_get_config(matrix_mdev); > + if (ret) { > + mutex_unlock(&matrix_dev->mdevs_lock); > + return ret; > + } > + } What's the point of this block? Under what circumstances can we get here not having set mig_file->ap_config? > + > + /* > + * Compute the offset and clamped length fully under the lock so that > + * concurrent read()s on this stream file each see a consistent view of > + * the current position. *pos is advanced here while we still hold the > + * lock; copy_to_user() then uses the snapshot read_pos. This prevents > + * two threads from calculating the same offset and both copying the > + * same region (or one reading past the end of the buffer). > + */ > + if (*pos >= mig_file->config_sz) { > + mutex_unlock(&matrix_dev->mdevs_lock); > + return 0; > + } > + > + len = min_t(size_t, mig_file->config_sz - *pos, len); > + if (len == 0) { > + mutex_unlock(&matrix_dev->mdevs_lock); > + return 0; > + } > + > + read_pos = *pos; > + *pos += len; > + > + /* > + * Drop the lock only for the copy_to_user(). The ap_config buffer is > + * stable: it is allocated once in vfio_ap_get_config() and freed only > + * in vfio_ap_release_stop_copy_file() which requires mdevs_lock. > + * Since we already advanced *pos above, no other thread will compute an > + * overlapping region. > + */ > + mutex_unlock(&matrix_dev->mdevs_lock); > + > + if (copy_to_user(buf, (char *)mig_file->ap_config + read_pos, len)) > + return -EFAULT; > + > + return len; > +} > + > static const struct file_operations vfio_ap_stop_copy_fops = { > .owner = THIS_MODULE, > .read = vfio_ap_stop_copy_read,