[Linaro-mm-sig] Fwd: [PATCH 4/4] vfio/pci: Allow MMIO regions to be exported through dma-buf

On Wed, Aug 17, 2022 at 7:11 PM Jason Gunthorpe jgg@nvidia.com 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@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);
  

•   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);
  

Before calling sg_free_table(), you need to restore the orig_nents as it is used in that function to free the allocated memory of the 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