[PATCH 4/4] vfio/pci: Allow MMIO regions to be exported through dma-buf
Yan Zhao
yan.y.zhao at intel.com
Mon Aug 29 05:04:05 UTC 2022
On Wed, Aug 17, 2022 at 01:11:42PM -0300, Jason Gunthorpe wrote:
> dma-buf has become a way to safely acquire a handle to non-struct page
> memory that can still have lifetime controlled by the exporter. Notably
> RDMA can now import dma-buf FDs and build them into MRs which allows for
> PCI P2P operations. Extend this to allow vfio-pci to export MMIO memory
> from PCI device BARs.
>
> The patch design loosely follows the pattern in commit
> db1a8dd916aa ("habanalabs: add support for dma-buf exporter") except this
> does not support pinning.
>
> Instead, this implements what, in the past, we've called a revocable
> attachment using move. In normal situations the attachment is pinned, as a
> BAR does not change physical address. However when the VFIO device is
> closed, or a PCI reset is issued, access to the MMIO memory is revoked.
>
> Revoked means that move occurs, but an attempt to immediately re-map the
> memory will fail. In the reset case a future move will be triggered when
> MMIO access returns. As both close and reset are under userspace control
> it is expected that userspace will suspend use of the dma-buf before doing
> these operations, the revoke is purely for kernel self-defense against a
> hostile userspace.
>
> Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>
> ---
> drivers/vfio/pci/Makefile | 1 +
> drivers/vfio/pci/vfio_pci_config.c | 8 +-
> drivers/vfio/pci/vfio_pci_core.c | 28 ++-
> drivers/vfio/pci/vfio_pci_dma_buf.c | 265 ++++++++++++++++++++++++++++
> drivers/vfio/pci/vfio_pci_priv.h | 23 +++
> include/linux/vfio_pci_core.h | 1 +
> include/uapi/linux/vfio.h | 18 ++
> 7 files changed, 336 insertions(+), 8 deletions(-)
> create mode 100644 drivers/vfio/pci/vfio_pci_dma_buf.c
>
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index 24c524224da5a3..81006a157cde14 100644
> --- a/drivers/vfio/pci/Makefile
> +++ b/drivers/vfio/pci/Makefile
> @@ -2,6 +2,7 @@
>
> vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
> vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
> +vfio-pci-core-$(CONFIG_DMA_SHARED_BUFFER) += vfio_pci_dma_buf.o
> obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
>
> vfio-pci-y := vfio_pci.o
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index d22921efa25987..f8a9c24d04aeb7 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -584,10 +584,12 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
> virt_mem = !!(le16_to_cpu(*virt_cmd) & PCI_COMMAND_MEMORY);
> new_mem = !!(new_cmd & PCI_COMMAND_MEMORY);
>
> - if (!new_mem)
> + if (!new_mem) {
> vfio_pci_zap_and_down_write_memory_lock(vdev);
> - else
> + vfio_pci_dma_buf_move(vdev, true);
> + } else {
> down_write(&vdev->memory_lock);
> + }
>
> /*
> * If the user is writing mem/io enable (new_mem/io) and we
> @@ -622,6 +624,8 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
> *virt_cmd &= cpu_to_le16(~mask);
> *virt_cmd |= cpu_to_le16(new_cmd & mask);
>
> + if (__vfio_pci_memory_enabled(vdev))
> + vfio_pci_dma_buf_move(vdev, false);
> up_write(&vdev->memory_lock);
> }
>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index d13e22021860cc..206f159c480e42 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -504,6 +504,8 @@ void vfio_pci_core_close_device(struct vfio_device *core_vdev)
> vfio_spapr_pci_eeh_release(vdev->pdev);
> vfio_pci_core_disable(vdev);
>
> + vfio_pci_dma_buf_cleanup(vdev);
> +
> mutex_lock(&vdev->igate);
> if (vdev->err_trigger) {
> eventfd_ctx_put(vdev->err_trigger);
> @@ -980,7 +982,10 @@ int vfio_pci_try_reset_function(struct vfio_pci_core_device *vdev)
> */
> vfio_pci_set_power_state(vdev, PCI_D0);
>
> + vfio_pci_dma_buf_move(vdev, true);
> ret = pci_try_reset_function(vdev->pdev);
> + if (__vfio_pci_memory_enabled(vdev))
> + vfio_pci_dma_buf_move(vdev, false);
> up_write(&vdev->memory_lock);
>
> return ret;
> @@ -1210,11 +1215,10 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
> }
> EXPORT_SYMBOL_GPL(vfio_pci_core_ioctl);
>
> -static int vfio_pci_core_feature_token(struct vfio_device *device, u32 flags,
> - uuid_t __user *arg, size_t argsz)
> +static int vfio_pci_core_feature_token(struct vfio_pci_core_device *vdev,
> + u32 flags, uuid_t __user *arg,
> + size_t argsz)
> {
> - struct vfio_pci_core_device *vdev =
> - container_of(device, struct vfio_pci_core_device, vdev);
> uuid_t uuid;
> int ret;
>
> @@ -1241,9 +1245,14 @@ static int vfio_pci_core_feature_token(struct vfio_device *device, u32 flags,
> int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
> void __user *arg, size_t argsz)
> {
> + struct vfio_pci_core_device *vdev =
> + container_of(device, struct vfio_pci_core_device, vdev);
> +
> switch (flags & VFIO_DEVICE_FEATURE_MASK) {
> case VFIO_DEVICE_FEATURE_PCI_VF_TOKEN:
> - return vfio_pci_core_feature_token(device, flags, arg, argsz);
> + return vfio_pci_core_feature_token(vdev, flags, arg, argsz);
> + case VFIO_DEVICE_FEATURE_DMA_BUF:
> + return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
> default:
> return -ENOTTY;
> }
> @@ -1881,6 +1890,7 @@ void vfio_pci_core_init_device(struct vfio_pci_core_device *vdev,
> INIT_LIST_HEAD(&vdev->vma_list);
> INIT_LIST_HEAD(&vdev->sriov_pfs_item);
> init_rwsem(&vdev->memory_lock);
> + INIT_LIST_HEAD(&vdev->dmabufs);
> }
> EXPORT_SYMBOL_GPL(vfio_pci_core_init_device);
>
> @@ -2227,11 +2237,17 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
> * cause the PCI config space reset without restoring the original
> * state (saved locally in 'vdev->pm_save').
> */
> - list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list)
> + list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
> + vfio_pci_dma_buf_move(cur, true);
> vfio_pci_set_power_state(cur, PCI_D0);
> + }
>
> ret = pci_reset_bus(pdev);
>
> + list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list)
> + if (__vfio_pci_memory_enabled(cur))
> + vfio_pci_dma_buf_move(cur, false);
> +
> err_undo:
> list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
> if (cur == cur_mem)
> diff --git a/drivers/vfio/pci/vfio_pci_dma_buf.c b/drivers/vfio/pci/vfio_pci_dma_buf.c
> new file mode 100644
> index 00000000000000..ac32405de5e48d
> --- /dev/null
> +++ b/drivers/vfio/pci/vfio_pci_dma_buf.c
> @@ -0,0 +1,265 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES.
> + */
> +#include <linux/dma-buf.h>
> +#include <linux/pci-p2pdma.h>
> +#include <linux/dma-resv.h>
> +
> +#include "vfio_pci_priv.h"
> +
> +MODULE_IMPORT_NS(DMA_BUF);
> +
> +struct vfio_pci_dma_buf {
> + struct dma_buf *dmabuf;
> + struct vfio_pci_core_device *vdev;
> + struct list_head dmabufs_elm;
> + unsigned int index;
> + size_t offset;
> + bool revoked;
> +};
> +
> +static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
> + struct dma_buf_attachment *attachment)
> +{
> + struct vfio_pci_dma_buf *priv = dmabuf->priv;
> + int rc;
> +
> + rc = pci_p2pdma_distance_many(priv->vdev->pdev, &attachment->dev, 1,
> + true);
> + if (rc < 0)
> + attachment->peer2peer = false;
> + return 0;
> +}
> +
> +static void vfio_pci_dma_buf_unpin(struct dma_buf_attachment *attachment)
> +{
> +}
> +
> +static int vfio_pci_dma_buf_pin(struct dma_buf_attachment *attachment)
> +{
> + /*
> + * Uses the dynamic interface but must always allow for
> + * dma_buf_move_notify() to do revoke
> + */
> + return -EINVAL;
> +}
> +
> +static struct sg_table *
> +vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment,
> + enum dma_data_direction dir)
> +{
> + size_t sgl_size = dma_get_max_seg_size(attachment->dev);
> + struct vfio_pci_dma_buf *priv = attachment->dmabuf->priv;
> + struct scatterlist *sgl;
> + struct sg_table *sgt;
> + dma_addr_t dma_addr;
> + unsigned int nents;
> + size_t offset;
> + int ret;
> +
> + dma_resv_assert_held(priv->dmabuf->resv);
> +
> + if (!attachment->peer2peer)
> + return ERR_PTR(-EPERM);
> +
> + if (!priv->revoked)
> + return ERR_PTR(-ENODEV);
> +
> + sgt = kzalloc(sizeof(*sgt), GFP_KERNEL);
> + if (!sgt)
> + return ERR_PTR(-ENOMEM);
> +
> + nents = DIV_ROUND_UP(priv->dmabuf->size, sgl_size);
> + ret = sg_alloc_table(sgt, nents, GFP_KERNEL);
> + if (ret)
> + goto err_kfree_sgt;
> +
> + /*
> + * Since the memory being mapped is a device memory it could never be in
> + * CPU caches.
> + */
> + dma_addr = dma_map_resource(
> + attachment->dev,
> + pci_resource_start(priv->vdev->pdev, priv->index) +
> + priv->offset,
> + priv->dmabuf->size, dir, DMA_ATTR_SKIP_CPU_SYNC);
dma_map_resource maps the phys to an IOVA in device's
default_domain, which, however, may not be the domain that the device is
currently attached to.
So, the importer of this sgt will convert this dma_addr back to phys?
BTW, I don't see the assignment of priv->index in below
vfio_pci_core_feature_dma_buf(), is it equal to get_dma_buf.region_index ?
Thanks
Yan
> + ret = dma_mapping_error(attachment->dev, dma_addr);
> + if (ret)
> + goto err_free_sgt;
> +
> + /*
> + * Break the BAR's physical range up into max sized SGL's according to
> + * the device's requirement.
> + */
> + sgl = sgt->sgl;
> + for (offset = 0; offset != priv->dmabuf->size;) {
> + size_t chunk_size = min(priv->dmabuf->size - offset, sgl_size);
> +
> + sg_set_page(sgl, NULL, chunk_size, 0);
> + sg_dma_address(sgl) = dma_addr + offset;
> + sg_dma_len(sgl) = chunk_size;
> + sgl = sg_next(sgl);
> + offset += chunk_size;
> + }
> +
> + /*
> + * Because we are not going to include a CPU list we want to have some
> + * chance that other users will detect this by setting the orig_nents to
> + * 0 and using only nents (length of DMA list) when going over the sgl
> + */
> + sgt->orig_nents = 0;
> + return sgt;
> +
> +err_free_sgt:
> + sg_free_table(sgt);
> +err_kfree_sgt:
> + kfree(sgt);
> + return ERR_PTR(ret);
> +}
> +
> +static void vfio_pci_dma_buf_unmap(struct dma_buf_attachment *attachment,
> + struct sg_table *sgt,
> + enum dma_data_direction dir)
> +{
> + struct vfio_pci_dma_buf *priv = attachment->dmabuf->priv;
> +
> + dma_unmap_resource(attachment->dev, sg_dma_address(sgt->sgl),
> + priv->dmabuf->size, dir, DMA_ATTR_SKIP_CPU_SYNC);
> + sg_free_table(sgt);
> + kfree(sgt);
> +}
> +
> +static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
> +{
> + struct vfio_pci_dma_buf *priv = dmabuf->priv;
> +
> + /*
> + * Either this or vfio_pci_dma_buf_cleanup() will remove from the list.
> + * The refcount prevents both.
> + */
> + if (priv->vdev) {
> + down_write(&priv->vdev->memory_lock);
> + list_del_init(&priv->dmabufs_elm);
> + up_write(&priv->vdev->memory_lock);
> + vfio_device_put(&priv->vdev->vdev);
> + }
> + kfree(priv);
> +}
> +
> +static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
> + .attach = vfio_pci_dma_buf_attach,
> + .map_dma_buf = vfio_pci_dma_buf_map,
> + .pin = vfio_pci_dma_buf_pin,
> + .unpin = vfio_pci_dma_buf_unpin,
> + .release = vfio_pci_dma_buf_release,
> + .unmap_dma_buf = vfio_pci_dma_buf_unmap,
> +};
> +
> +int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
> + struct vfio_device_feature_dma_buf __user *arg,
> + size_t argsz)
> +{
> + struct vfio_device_feature_dma_buf get_dma_buf;
> + DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> + struct vfio_pci_dma_buf *priv;
> + int ret;
> +
> + ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
> + sizeof(get_dma_buf));
> + if (ret != 1)
> + return ret;
> +
> + if (copy_from_user(&get_dma_buf, arg, sizeof(get_dma_buf)))
> + return -EFAULT;
> +
> + /* For PCI the region_index is the BAR number like everything else */
> + if (get_dma_buf.region_index >= VFIO_PCI_ROM_REGION_INDEX)
> + return -EINVAL;
> +
> + exp_info.ops = &vfio_pci_dmabuf_ops;
> + exp_info.size = pci_resource_len(vdev->pdev, get_dma_buf.region_index);
> + if (!exp_info.size)
> + return -EINVAL;
> + if (get_dma_buf.offset || get_dma_buf.length) {
> + if (get_dma_buf.length > exp_info.size ||
> + get_dma_buf.offset >= exp_info.size ||
> + get_dma_buf.length > exp_info.size - get_dma_buf.offset ||
> + get_dma_buf.offset % PAGE_SIZE ||
> + get_dma_buf.length % PAGE_SIZE)
> + return -EINVAL;
> + exp_info.size = get_dma_buf.length;
> + }
> + exp_info.flags = get_dma_buf.open_flags;
> +
> + priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> + if (!priv)
> + return -ENOMEM;
> + INIT_LIST_HEAD(&priv->dmabufs_elm);
> + priv->offset = get_dma_buf.offset;
> +
> + exp_info.priv = priv;
> + priv->dmabuf = dma_buf_export(&exp_info);
> + if (IS_ERR(priv->dmabuf)) {
> + ret = PTR_ERR(priv->dmabuf);
> + kfree(priv);
> + return ret;
> + }
> +
> + /* dma_buf_put() now frees priv */
> +
> + down_write(&vdev->memory_lock);
> + dma_resv_lock(priv->dmabuf->resv, NULL);
> + priv->revoked = __vfio_pci_memory_enabled(vdev);
> + priv->vdev = vdev;
> + vfio_device_get(&vdev->vdev);
> + list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
> + dma_resv_unlock(priv->dmabuf->resv);
> + up_write(&vdev->memory_lock);
> +
> + /*
> + * dma_buf_fd() consumes the reference, when the file closes the dmabuf
> + * will be released.
> + */
> + return dma_buf_fd(priv->dmabuf, get_dma_buf.open_flags);
> +}
> +
> +void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
> +{
> + struct vfio_pci_dma_buf *priv;
> + struct vfio_pci_dma_buf *tmp;
> +
> + lockdep_assert_held_write(&vdev->memory_lock);
> +
> + list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
> + if (!dma_buf_try_get(priv->dmabuf))
> + continue;
> + if (priv->revoked != revoked) {
> + dma_resv_lock(priv->dmabuf->resv, NULL);
> + priv->revoked = revoked;
> + dma_buf_move_notify(priv->dmabuf);
> + dma_resv_unlock(priv->dmabuf->resv);
> + }
> + dma_buf_put(priv->dmabuf);
> + }
> +}
> +
> +void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
> +{
> + struct vfio_pci_dma_buf *priv;
> + struct vfio_pci_dma_buf *tmp;
> +
> + down_write(&vdev->memory_lock);
> + list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
> + if (!dma_buf_try_get(priv->dmabuf))
> + continue;
> + dma_resv_lock(priv->dmabuf->resv, NULL);
> + list_del_init(&priv->dmabufs_elm);
> + priv->vdev = NULL;
> + priv->revoked = true;
> + dma_buf_move_notify(priv->dmabuf);
> + dma_resv_unlock(priv->dmabuf->resv);
> + vfio_device_put(&vdev->vdev);
> + dma_buf_put(priv->dmabuf);
> + }
> + up_write(&vdev->memory_lock);
> +}
> diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
> index 5b1cb9a9838442..c295a1166e7a9c 100644
> --- a/drivers/vfio/pci/vfio_pci_priv.h
> +++ b/drivers/vfio/pci/vfio_pci_priv.h
> @@ -102,4 +102,27 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
> return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
> }
>
> +#ifdef CONFIG_DMA_SHARED_BUFFER
> +int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
> + struct vfio_device_feature_dma_buf __user *arg,
> + size_t argsz);
> +void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
> +void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
> +#else
> +static int
> +vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
> + struct vfio_device_feature_dma_buf __user *arg,
> + size_t argsz)
> +{
> + return -ENOTTY;
> +}
> +static inline void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
> +{
> +}
> +static inline void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev,
> + bool revoked)
> +{
> +}
> +#endif
> +
> #endif
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index 9d18b832e61a0d..b57f4ecc2665e1 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -93,6 +93,7 @@ struct vfio_pci_core_device {
> struct mutex vma_lock;
> struct list_head vma_list;
> struct rw_semaphore memory_lock;
> + struct list_head dmabufs;
> };
>
> /* Will be exported for vfio pci drivers usage */
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 733a1cddde30a5..1dcfad6dcb6863 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -986,6 +986,24 @@ enum vfio_device_mig_state {
> VFIO_DEVICE_STATE_RUNNING_P2P = 5,
> };
>
> +/**
> + * Upon VFIO_DEVICE_FEATURE_GET create a dma_buf fd for the
> + * region selected.
> + *
> + * open_flags are the typical flags passed to open(2), eg O_RDWR, O_CLOEXEC,
> + * etc. offset/length specify a slice of the region to create the dmabuf from.
> + * If both are 0 then the whole region is used.
> + *
> + * Return: The fd number on success, -1 and errno is set on failure.
> + */
> +struct vfio_device_feature_dma_buf {
> + __u32 region_index;
> + __u32 open_flags;
> + __u32 offset;
> + __u64 length;
> +};
> +#define VFIO_DEVICE_FEATURE_DMA_BUF 3
> +
> /* -------- API for Type1 VFIO IOMMU -------- */
>
> /**
> --
> 2.37.2
>
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