[SRU][J:linux-bluefield][PATCH v5 4/6] UBUNTU: SAUCE: vfio/pci: Allow MMIO regions to be exported through dma-buf
Bartlomiej Zolnierkiewicz
bartlomiej.zolnierkiewicz at canonical.com
Mon Sep 23 13:15:17 UTC 2024
On Mon, Sep 16, 2024 at 5:32 PM William Tu <witu at nvidia.com> wrote:
>
> From: Jason Gunthorpe <jgg at nvidia.com>
>
> BugLink: https://bugs.launchpad.net/bugs/2077887
>
> 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.
>
> Co-authored-by: William Tu <witu at nvidia.com>
> [witu: Add new ioctl uAPI for P2P dma buf]
> Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>
> Signed-off-by: William Tu <witu at nvidia.com>
> ---
> drivers/vfio/pci/Makefile | 1 +
> drivers/vfio/pci/dma_buf.c | 262 +++++++++++++++++++++++++++++
> drivers/vfio/pci/vfio_pci_config.c | 10 +-
> drivers/vfio/pci/vfio_pci_core.c | 23 ++-
> drivers/vfio/pci/vfio_pci_priv.h | 21 +++
> include/linux/vfio_pci_core.h | 1 +
> include/uapi/linux/vfio.h | 28 +++
> 7 files changed, 342 insertions(+), 4 deletions(-)
> create mode 100644 drivers/vfio/pci/dma_buf.c
>
> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
> index 74ee55f9c261..14f198c9d9ea 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) += dma_buf.o
> obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
>
> vfio-pci-y := vfio_pci.o
> diff --git a/drivers/vfio/pci/dma_buf.c b/drivers/vfio/pci/dma_buf.c
> new file mode 100644
> index 000000000000..14d32a580190
> --- /dev/null
> +++ b/drivers/vfio/pci/dma_buf.c
> @@ -0,0 +1,262 @@
> +// 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;
> + unsigned int orig_nents;
> + 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
> + */
> + priv->orig_nents = sgt->orig_nents;
> + 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;
> +
> + sgt->orig_nents = priv->orig_nents;
> + 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,
> + struct vfio_device_p2p_dma_buf *p2p_dma_buf)
> +{
> + struct vfio_device_p2p_dma_buf get_dma_buf;
> + DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> + struct vfio_pci_dma_buf *priv;
> + int ret;
> +
> + memcpy(&get_dma_buf, p2p_dma_buf, sizeof(get_dma_buf));
> +
> + /* 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;
> + priv->index = get_dma_buf.region_index;
> +
> + 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_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index 78c626b8907d..f14a8b81fe35 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -28,6 +28,8 @@
>
> #include <linux/vfio_pci_core.h>
>
> +#include "vfio_pci_priv.h"
> +
> /* Fake capability ID for standard config space */
> #define PCI_CAP_ID_BASIC 0
>
> @@ -581,10 +583,12 @@ 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
> @@ -619,6 +623,8 @@ 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 a45cdd3cfb84..4e8fec2315f7 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -465,6 +465,8 @@ 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);
> @@ -671,7 +673,10 @@ 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;
> @@ -1206,6 +1211,14 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
> default:
> return -ENOTTY;
> }
> + } else if (cmd == VFIO_DEVICE_P2P_DMA_BUF) {
> + struct vfio_device_p2p_dma_buf p2p_dma_buf;
> +
> + if (copy_from_user(&p2p_dma_buf, (void __user *)arg,
> + sizeof(p2p_dma_buf)))
> + return -EFAULT;
> +
> + return vfio_pci_core_feature_dma_buf(vdev, &p2p_dma_buf);
> }
>
> return -ENOTTY;
> @@ -1839,6 +1852,7 @@ 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);
>
> @@ -2151,11 +2165,16 @@ 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)
> - vfio_pci_set_power_state(cur, PCI_D0);
> + list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
> + vfio_pci_dma_buf_move(cur, true);
> + }
The above code remains incorrect as it still removes
vfio_pci_set_power_state() call.
Could you please fix it?
> 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_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
> index 4971cd95b431..d60e9cb99140 100644
> --- a/drivers/vfio/pci/vfio_pci_priv.h
> +++ b/drivers/vfio/pci/vfio_pci_priv.h
> @@ -4,4 +4,25 @@
>
> int vfio_pci_try_reset_function(struct vfio_pci_core_device *vdev);
>
> +#ifdef CONFIG_DMA_SHARED_BUFFER
> +int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev,
> + struct vfio_device_p2p_dma_buf *arg);
> +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,
> + struct vfio_device_p2p_dma_buf *arg)
> +{
> + 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 f22d5a382c15..1136ed4a08f9 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -139,6 +139,7 @@ struct vfio_pci_core_device {
> struct mutex vma_lock;
> struct list_head vma_list;
> struct rw_semaphore memory_lock;
> + struct list_head dmabufs;
> };
>
> #define is_intx(vdev) (vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX)
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index ef33ea002b0b..18f369426c13 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -1002,6 +1002,34 @@ struct vfio_device_feature {
> */
> #define VFIO_DEVICE_FEATURE_PCI_VF_TOKEN (0)
>
> +/**
> + * Upon VFIO_DEVICE_FEATURE_GET create a dma_buf fd for the
> + * region selected.
The above comment seems incorrect as now this feature uses its own ioctl.
--
Best regards,
Bartlomiej
> + *
> + * 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.
> + */
> +
> +/**
> + * VFIO_DEVICE_P2P_DMA_BUF - _IORW(VFIO_TYPE, VFIO_BASE + 22,
> + * struct vfio_device_p2p_dma_buf)
> + *
> + * Set the region index, open flags, offset and length to create a dma_buf
> + * for p2p dma.
> + *
> + * Return 0 on success, -errno on failure.
> + */
> +struct vfio_device_p2p_dma_buf {
> + __u32 region_index;
> + __u32 open_flags;
> + __u32 offset;
> + __u64 length;
> +};
> +#define VFIO_DEVICE_P2P_DMA_BUF _IO(VFIO_TYPE, VFIO_BASE + 22)
> +
> /* -------- API for Type1 VFIO IOMMU -------- */
>
> /**
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