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Date:   Wed, 12 Sep 2018 12:57:07 -0400
From:   Luiz Capitulino <lcapitulino@redhat.com>
To:     Pankaj Gupta <pagupta@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        qemu-devel@nongnu.org, linux-nvdimm@ml01.01.org, jack@suse.cz,
        stefanha@redhat.com, dan.j.williams@intel.com, riel@surriel.com,
        nilal@redhat.com, kwolf@redhat.com, pbonzini@redhat.com,
        ross.zwisler@intel.com, david@redhat.com,
        xiaoguangrong.eric@gmail.com, hch@infradead.org, mst@redhat.com,
        niteshnarayanlal@hotmail.com, imammedo@redhat.com,
        eblake@redhat.com
Subject: Re: [PATCH] qemu: Add virtio pmem device
Message-ID: <20180912125707.58df7dc5@doriath>
In-Reply-To: <20180831133019.27579-5-pagupta@redhat.com>
References: <20180831133019.27579-1-pagupta@redhat.com>
        <20180831133019.27579-5-pagupta@redhat.com>
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On Fri, 31 Aug 2018 19:00:19 +0530
Pankaj Gupta <pagupta@redhat.com> wrote:

>  This patch adds virtio-pmem Qemu device.
> 
>  This device presents memory address range information to guest
>  which is backed by file backend type. It acts like persistent
>  memory device for KVM guest. Guest can perform read and 
>  persistent write operations on this memory range with the help 
>  of DAX capable filesystem.
> 
>  Persistent guest writes are assured with the help of virtio 
>  based flushing interface. When guest userspace space performs 
>  fsync on file fd on pmem device, a flush command is send to 
>  Qemu over VIRTIO and host side flush/sync is done on backing 
>  image file.
> 
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
> Changes from RFC v3:
> - Return EIO for host fsync failure instead of errno - Luiz, Stefan
> - Change version for inclusion to Qemu 3.1 - Eric
> 
> Changes from RFC v2:
> - Use aio_worker() to avoid Qemu from hanging with blocking fsync
>   call - Stefan
> - Use virtio_st*_p() for endianess - Stefan
> - Correct indentation in qapi/misc.json - Eric
> 
>  hw/virtio/Makefile.objs                     |   3 +
>  hw/virtio/virtio-pci.c                      |  44 +++++
>  hw/virtio/virtio-pci.h                      |  14 ++
>  hw/virtio/virtio-pmem.c                     | 241 ++++++++++++++++++++++++++++
>  include/hw/pci/pci.h                        |   1 +
>  include/hw/virtio/virtio-pmem.h             |  42 +++++
>  include/standard-headers/linux/virtio_ids.h |   1 +
>  qapi/misc.json                              |  26 ++-
>  8 files changed, 371 insertions(+), 1 deletion(-)
>  create mode 100644 hw/virtio/virtio-pmem.c
>  create mode 100644 include/hw/virtio/virtio-pmem.h
> 
> diff --git a/hw/virtio/Makefile.objs b/hw/virtio/Makefile.objs
> index 1b2799cfd8..7f914d45d0 100644
> --- a/hw/virtio/Makefile.objs
> +++ b/hw/virtio/Makefile.objs
> @@ -10,6 +10,9 @@ obj-$(CONFIG_VIRTIO_CRYPTO) += virtio-crypto.o
>  obj-$(call land,$(CONFIG_VIRTIO_CRYPTO),$(CONFIG_VIRTIO_PCI)) += virtio-crypto-pci.o
>  
>  obj-$(CONFIG_LINUX) += vhost.o vhost-backend.o vhost-user.o
> +ifeq ($(CONFIG_MEM_HOTPLUG),y)
> +obj-$(CONFIG_LINUX) += virtio-pmem.o
> +endif
>  obj-$(CONFIG_VHOST_VSOCK) += vhost-vsock.o
>  endif
>  
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 3a01fe90f0..93d3fc05c7 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -2521,6 +2521,49 @@ static const TypeInfo virtio_rng_pci_info = {
>      .class_init    = virtio_rng_pci_class_init,
>  };
>  
> +/* virtio-pmem-pci */
> +
> +static void virtio_pmem_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
> +{
> +    VirtIOPMEMPCI *vpmem = VIRTIO_PMEM_PCI(vpci_dev);
> +    DeviceState *vdev = DEVICE(&vpmem->vdev);
> +
> +    qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> +    object_property_set_bool(OBJECT(vdev), true, "realized", errp);
> +}
> +
> +static void virtio_pmem_pci_class_init(ObjectClass *klass, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(klass);
> +    VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
> +    PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
> +    k->realize = virtio_pmem_pci_realize;
> +    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
> +    pcidev_k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
> +    pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_PMEM;
> +    pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
> +    pcidev_k->class_id = PCI_CLASS_OTHERS;
> +}
> +
> +static void virtio_pmem_pci_instance_init(Object *obj)
> +{
> +    VirtIOPMEMPCI *dev = VIRTIO_PMEM_PCI(obj);
> +
> +    virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
> +                                TYPE_VIRTIO_PMEM);
> +    object_property_add_alias(obj, "memdev", OBJECT(&dev->vdev), "memdev",
> +                              &error_abort);
> +}
> +
> +static const TypeInfo virtio_pmem_pci_info = {
> +    .name          = TYPE_VIRTIO_PMEM_PCI,
> +    .parent        = TYPE_VIRTIO_PCI,
> +    .instance_size = sizeof(VirtIOPMEMPCI),
> +    .instance_init = virtio_pmem_pci_instance_init,
> +    .class_init    = virtio_pmem_pci_class_init,
> +};
> +
> +
>  /* virtio-input-pci */
>  
>  static Property virtio_input_pci_properties[] = {
> @@ -2714,6 +2757,7 @@ static void virtio_pci_register_types(void)
>      type_register_static(&virtio_balloon_pci_info);
>      type_register_static(&virtio_serial_pci_info);
>      type_register_static(&virtio_net_pci_info);
> +    type_register_static(&virtio_pmem_pci_info);
>  #ifdef CONFIG_VHOST_SCSI
>      type_register_static(&vhost_scsi_pci_info);
>  #endif
> diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
> index 813082b0d7..fe74fcad3f 100644
> --- a/hw/virtio/virtio-pci.h
> +++ b/hw/virtio/virtio-pci.h
> @@ -19,6 +19,7 @@
>  #include "hw/virtio/virtio-blk.h"
>  #include "hw/virtio/virtio-net.h"
>  #include "hw/virtio/virtio-rng.h"
> +#include "hw/virtio/virtio-pmem.h"
>  #include "hw/virtio/virtio-serial.h"
>  #include "hw/virtio/virtio-scsi.h"
>  #include "hw/virtio/virtio-balloon.h"
> @@ -57,6 +58,7 @@ typedef struct VirtIOInputHostPCI VirtIOInputHostPCI;
>  typedef struct VirtIOGPUPCI VirtIOGPUPCI;
>  typedef struct VHostVSockPCI VHostVSockPCI;
>  typedef struct VirtIOCryptoPCI VirtIOCryptoPCI;
> +typedef struct VirtIOPMEMPCI VirtIOPMEMPCI;
>  
>  /* virtio-pci-bus */
>  
> @@ -274,6 +276,18 @@ struct VirtIOBlkPCI {
>      VirtIOBlock vdev;
>  };
>  
> +/*
> + * virtio-pmem-pci: This extends VirtioPCIProxy.
> + */
> +#define TYPE_VIRTIO_PMEM_PCI "virtio-pmem-pci"
> +#define VIRTIO_PMEM_PCI(obj) \
> +        OBJECT_CHECK(VirtIOPMEMPCI, (obj), TYPE_VIRTIO_PMEM_PCI)
> +
> +struct VirtIOPMEMPCI {
> +    VirtIOPCIProxy parent_obj;
> +    VirtIOPMEM vdev;
> +};
> +
>  /*
>   * virtio-balloon-pci: This extends VirtioPCIProxy.
>   */
> diff --git a/hw/virtio/virtio-pmem.c b/hw/virtio/virtio-pmem.c
> new file mode 100644
> index 0000000000..69ae4c0a50
> --- /dev/null
> +++ b/hw/virtio/virtio-pmem.c
> @@ -0,0 +1,241 @@
> +/*
> + * Virtio pmem device
> + *
> + * Copyright (C) 2018 Red Hat, Inc.
> + * Copyright (C) 2018 Pankaj Gupta <pagupta@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "qemu-common.h"
> +#include "qemu/error-report.h"
> +#include "hw/virtio/virtio-access.h"
> +#include "hw/virtio/virtio-pmem.h"
> +#include "hw/mem/memory-device.h"
> +#include "block/aio.h"
> +#include "block/thread-pool.h"
> +
> +typedef struct VirtIOPMEMresp {
> +    int ret;
> +} VirtIOPMEMResp;
> +
> +typedef struct VirtIODeviceRequest {
> +    VirtQueueElement elem;
> +    int fd;
> +    VirtIOPMEM *pmem;
> +    VirtIOPMEMResp resp;
> +} VirtIODeviceRequest;
> +
> +static int worker_cb(void *opaque)
> +{
> +    VirtIODeviceRequest *req = opaque;
> +    int err = 0;
> +
> +    /* flush raw backing image */
> +    err = fsync(req->fd);
> +    if (err != 0) {
> +        err = EIO;
> +    }
> +    req->resp.ret = err;

As I mentioned in the kernel patch, I think you should 1 for
error and let the guest pick the error it wants to return to
the calling thread.

> +
> +    return 0;
> +}
> +
> +static void done_cb(void *opaque, int ret)
> +{
> +    VirtIODeviceRequest *req = opaque;
> +    int len = iov_from_buf(req->elem.in_sg, req->elem.in_num, 0,
> +                              &req->resp, sizeof(VirtIOPMEMResp));
> +
> +    /* Callbacks are serialized, so no need to use atomic ops.  */
> +    virtqueue_push(req->pmem->rq_vq, &req->elem, len);
> +    virtio_notify((VirtIODevice *)req->pmem, req->pmem->rq_vq);
> +    g_free(req);
> +}
> +
> +static void virtio_pmem_flush(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    VirtIODeviceRequest *req;
> +    VirtIOPMEM *pmem = VIRTIO_PMEM(vdev);
> +    HostMemoryBackend *backend = MEMORY_BACKEND(pmem->memdev);
> +    ThreadPool *pool = aio_get_thread_pool(qemu_get_aio_context());
> +
> +    req = virtqueue_pop(vq, sizeof(VirtIODeviceRequest));
> +    if (!req) {
> +        virtio_error(vdev, "virtio-pmem missing request data");
> +        return;
> +    }
> +
> +    if (req->elem.out_num < 1 || req->elem.in_num < 1) {
> +        virtio_error(vdev, "virtio-pmem request not proper");
> +        g_free(req);
> +        return;
> +    }

I think you should abort() in those errors.

> +    req->fd = memory_region_get_fd(&backend->mr);
> +    req->pmem = pmem;
> +    thread_pool_submit_aio(pool, worker_cb, req, done_cb, req);
> +}
> +
> +static void virtio_pmem_get_config(VirtIODevice *vdev, uint8_t *config)
> +{
> +    VirtIOPMEM *pmem = VIRTIO_PMEM(vdev);
> +    struct virtio_pmem_config *pmemcfg = (struct virtio_pmem_config *) config;
> +
> +    virtio_stq_p(vdev, &pmemcfg->start, pmem->start);
> +    virtio_stq_p(vdev, &pmemcfg->size, pmem->size);
> +}
> +
> +static uint64_t virtio_pmem_get_features(VirtIODevice *vdev, uint64_t features,
> +                                        Error **errp)
> +{
> +    return features;
> +}
> +
> +static void virtio_pmem_realize(DeviceState *dev, Error **errp)
> +{
> +    VirtIODevice   *vdev   = VIRTIO_DEVICE(dev);
> +    VirtIOPMEM     *pmem   = VIRTIO_PMEM(dev);
> +    MachineState   *ms     = MACHINE(qdev_get_machine());
> +    uint64_t align;
> +    Error *local_err = NULL;
> +    MemoryRegion *mr;
> +
> +    if (!pmem->memdev) {
> +        error_setg(errp, "virtio-pmem memdev not set");
> +        return;
> +    }
> +
> +    mr  = host_memory_backend_get_memory(pmem->memdev);
> +    align = memory_region_get_alignment(mr);
> +    pmem->size = QEMU_ALIGN_DOWN(memory_region_size(mr), align);
> +    pmem->start = memory_device_get_free_addr(ms, NULL, align, pmem->size,
> +                                                               &local_err);
> +    if (local_err) {
> +        error_setg(errp, "Can't get free address in mem device");
> +        return;
> +    }
> +    memory_region_init_alias(&pmem->mr, OBJECT(pmem),
> +                             "virtio_pmem-memory", mr, 0, pmem->size);
> +    memory_device_plug_region(ms, &pmem->mr, pmem->start);
> +
> +    host_memory_backend_set_mapped(pmem->memdev, true);
> +    virtio_init(vdev, TYPE_VIRTIO_PMEM, VIRTIO_ID_PMEM,
> +                                          sizeof(struct virtio_pmem_config));
> +    pmem->rq_vq = virtio_add_queue(vdev, 128, virtio_pmem_flush);
> +}
> +
> +static void virtio_mem_check_memdev(Object *obj, const char *name, Object *val,
> +                                    Error **errp)
> +{
> +    if (host_memory_backend_is_mapped(MEMORY_BACKEND(val))) {
> +        char *path = object_get_canonical_path_component(val);
> +        error_setg(errp, "Can't use already busy memdev: %s", path);
> +        g_free(path);
> +        return;
> +    }
> +
> +    qdev_prop_allow_set_link_before_realize(obj, name, val, errp);
> +}
> +
> +static const char *virtio_pmem_get_device_id(VirtIOPMEM *vm)
> +{
> +    Object *obj = OBJECT(vm);
> +    DeviceState *parent_dev;
> +
> +    /* always use the ID of the proxy device */
> +    if (obj->parent && object_dynamic_cast(obj->parent, TYPE_DEVICE)) {
> +        parent_dev = DEVICE(obj->parent);
> +        return parent_dev->id;
> +    }
> +    return NULL;
> +}
> +
> +static void virtio_pmem_md_fill_device_info(const MemoryDeviceState *md,
> +                                           MemoryDeviceInfo *info)
> +{
> +    VirtioPMemDeviceInfo *vi = g_new0(VirtioPMemDeviceInfo, 1);
> +    VirtIOPMEM *vm = VIRTIO_PMEM(md);
> +    const char *id = virtio_pmem_get_device_id(vm);
> +
> +    if (id) {
> +        vi->has_id = true;
> +        vi->id = g_strdup(id);
> +    }
> +
> +    vi->start = vm->start;
> +    vi->size = vm->size;
> +    vi->memdev = object_get_canonical_path(OBJECT(vm->memdev));
> +
> +    info->u.virtio_pmem.data = vi;
> +    info->type = MEMORY_DEVICE_INFO_KIND_VIRTIO_PMEM;
> +}
> +
> +static uint64_t virtio_pmem_md_get_addr(const MemoryDeviceState *md)
> +{
> +    VirtIOPMEM *vm = VIRTIO_PMEM(md);
> +
> +    return vm->start;
> +}
> +
> +static uint64_t virtio_pmem_md_get_plugged_size(const MemoryDeviceState *md)
> +{
> +    VirtIOPMEM *vm = VIRTIO_PMEM(md);
> +
> +    return vm->size;
> +}
> +
> +static uint64_t virtio_pmem_md_get_region_size(const MemoryDeviceState *md)
> +{
> +    VirtIOPMEM *vm = VIRTIO_PMEM(md);
> +
> +    return vm->size;
> +}
> +
> +static void virtio_pmem_instance_init(Object *obj)
> +{
> +    VirtIOPMEM *vm = VIRTIO_PMEM(obj);
> +    object_property_add_link(obj, "memdev", TYPE_MEMORY_BACKEND,
> +                                (Object **)&vm->memdev,
> +                                (void *) virtio_mem_check_memdev,
> +                                OBJ_PROP_LINK_STRONG,
> +                                &error_abort);
> +}
> +
> +
> +static void virtio_pmem_class_init(ObjectClass *klass, void *data)
> +{
> +    VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
> +    MemoryDeviceClass *mdc = MEMORY_DEVICE_CLASS(klass);
> +
> +    vdc->realize      =  virtio_pmem_realize;
> +    vdc->get_config   =  virtio_pmem_get_config;
> +    vdc->get_features =  virtio_pmem_get_features;
> +
> +    mdc->get_addr         = virtio_pmem_md_get_addr;
> +    mdc->get_plugged_size = virtio_pmem_md_get_plugged_size;
> +    mdc->get_region_size  = virtio_pmem_md_get_region_size;
> +    mdc->fill_device_info = virtio_pmem_md_fill_device_info;
> +}
> +
> +static TypeInfo virtio_pmem_info = {
> +    .name          = TYPE_VIRTIO_PMEM,
> +    .parent        = TYPE_VIRTIO_DEVICE,
> +    .class_init    = virtio_pmem_class_init,
> +    .instance_size = sizeof(VirtIOPMEM),
> +    .instance_init = virtio_pmem_instance_init,
> +    .interfaces = (InterfaceInfo[]) {
> +        { TYPE_MEMORY_DEVICE },
> +        { }
> +  },
> +};
> +
> +static void virtio_register_types(void)
> +{
> +    type_register_static(&virtio_pmem_info);
> +}
> +
> +type_init(virtio_register_types)
> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> index 990d6fcbde..28829b6437 100644
> --- a/include/hw/pci/pci.h
> +++ b/include/hw/pci/pci.h
> @@ -85,6 +85,7 @@ extern bool pci_available;
>  #define PCI_DEVICE_ID_VIRTIO_RNG         0x1005
>  #define PCI_DEVICE_ID_VIRTIO_9P          0x1009
>  #define PCI_DEVICE_ID_VIRTIO_VSOCK       0x1012
> +#define PCI_DEVICE_ID_VIRTIO_PMEM        0x1013
>  
>  #define PCI_VENDOR_ID_REDHAT             0x1b36
>  #define PCI_DEVICE_ID_REDHAT_BRIDGE      0x0001
> diff --git a/include/hw/virtio/virtio-pmem.h b/include/hw/virtio/virtio-pmem.h
> new file mode 100644
> index 0000000000..fda3ee691c
> --- /dev/null
> +++ b/include/hw/virtio/virtio-pmem.h
> @@ -0,0 +1,42 @@
> +/*
> + * Virtio pmem Device
> + *
> + * Copyright Red Hat, Inc. 2018
> + * Copyright Pankaj Gupta <pagupta@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or
> + * (at your option) any later version.  See the COPYING file in the
> + * top-level directory.
> + */
> +
> +#ifndef QEMU_VIRTIO_PMEM_H
> +#define QEMU_VIRTIO_PMEM_H
> +
> +#include "hw/virtio/virtio.h"
> +#include "exec/memory.h"
> +#include "sysemu/hostmem.h"
> +#include "standard-headers/linux/virtio_ids.h"
> +#include "hw/boards.h"
> +#include "hw/i386/pc.h"
> +
> +#define TYPE_VIRTIO_PMEM "virtio-pmem"
> +
> +#define VIRTIO_PMEM(obj) \
> +        OBJECT_CHECK(VirtIOPMEM, (obj), TYPE_VIRTIO_PMEM)
> +
> +/* VirtIOPMEM device structure */
> +typedef struct VirtIOPMEM {
> +    VirtIODevice parent_obj;
> +
> +    VirtQueue *rq_vq;
> +    uint64_t start;
> +    uint64_t size;
> +    MemoryRegion mr;
> +    HostMemoryBackend *memdev;
> +} VirtIOPMEM;
> +
> +struct virtio_pmem_config {
> +    uint64_t start;
> +    uint64_t size;
> +};
> +#endif
> diff --git a/include/standard-headers/linux/virtio_ids.h b/include/standard-headers/linux/virtio_ids.h
> index 6d5c3b2d4f..346389565a 100644
> --- a/include/standard-headers/linux/virtio_ids.h
> +++ b/include/standard-headers/linux/virtio_ids.h
> @@ -43,5 +43,6 @@
>  #define VIRTIO_ID_INPUT        18 /* virtio input */
>  #define VIRTIO_ID_VSOCK        19 /* virtio vsock transport */
>  #define VIRTIO_ID_CRYPTO       20 /* virtio crypto */
> +#define VIRTIO_ID_PMEM         25 /* virtio pmem */
>  
>  #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/qapi/misc.json b/qapi/misc.json
> index d450cfef21..517376b866 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -2907,6 +2907,29 @@
>            }
>  }
>  
> +##
> +# @VirtioPMemDeviceInfo:
> +#
> +# VirtioPMem state information
> +#
> +# @id: device's ID
> +#
> +# @start: physical address, where device is mapped
> +#
> +# @size: size of memory that the device provides
> +#
> +# @memdev: memory backend linked with device
> +#
> +# Since: 3.1
> +##
> +{ 'struct': 'VirtioPMemDeviceInfo',
> +  'data': { '*id': 'str',
> +            'start': 'size',
> +            'size': 'size',
> +            'memdev': 'str'
> +          }
> +}
> +
>  ##
>  # @MemoryDeviceInfo:
>  #
> @@ -2916,7 +2939,8 @@
>  ##
>  { 'union': 'MemoryDeviceInfo',
>    'data': { 'dimm': 'PCDIMMDeviceInfo',
> -            'nvdimm': 'PCDIMMDeviceInfo'
> +            'nvdimm': 'PCDIMMDeviceInfo',
> +	    'virtio-pmem': 'VirtioPMemDeviceInfo'
>            }
>  }
>