Re: [PATCH RFC] vhost: basic device IOTLB support
From: Michael S. Tsirkin
Date: Thu Dec 31 2015 - 06:17:46 EST
On Thu, Dec 31, 2015 at 03:13:45PM +0800, Jason Wang wrote:
> This patch tries to implement an device IOTLB for vhost. This could be
> used with for co-operation with userspace(qemu) implementation of
> iommu for a secure DMA environment in guest.
>
> The idea is simple. When vhost meets an IOTLB miss, it will request
> the assistance of userspace to do the translation, this is done
> through:
>
> - Fill the translation request in a preset userspace address (This
> address is set through ioctl VHOST_SET_IOTLB_REQUEST_ENTRY).
> - Notify userspace through eventfd (This eventfd was set through ioctl
> VHOST_SET_IOTLB_FD).
>
> When userspace finishes the translation, it will update the vhost
> IOTLB through VHOST_UPDATE_IOTLB ioctl. Userspace is also in charge of
> snooping the IOTLB invalidation of IOMMU IOTLB and use
> VHOST_UPDATE_IOTLB to invalidate the possible entry in vhost.
>
> For simplicity, IOTLB was implemented with a simple hash array. The
> index were calculated from IOVA page frame number which can only works
> at PAGE_SIZE level.
>
> An qemu implementation (for reference) is available at:
> git@xxxxxxxxxx:jasowang/qemu.git iommu
>
> TODO & Known issues:
>
> - read/write permission validation was not implemented.
> - no feature negotiation.
> - VHOST_SET_MEM_TABLE is not reused (maybe there's a chance).
> - working at PAGE_SIZE level, don't support large mappings.
> - better data structure for IOTLB instead of simple hash array.
> - better API, e.g using mmap() instead of preset userspace address.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Interesting. I'm working on a slightly different approach
which is direct vt-d support in vhost.
This one has the advantage of being more portable.
> ---
> drivers/vhost/net.c | 2 +-
> drivers/vhost/vhost.c | 190 ++++++++++++++++++++++++++++++++++++++++++++-
> drivers/vhost/vhost.h | 13 ++++
> include/uapi/linux/vhost.h | 26 +++++++
> 4 files changed, 229 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 9eda69e..a172be9 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -1083,7 +1083,7 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
> r = vhost_dev_ioctl(&n->dev, ioctl, argp);
> if (r == -ENOIOCTLCMD)
> r = vhost_vring_ioctl(&n->dev, ioctl, argp);
> - else
> + else if (ioctl != VHOST_UPDATE_IOTLB)
> vhost_net_flush(n);
> mutex_unlock(&n->dev.mutex);
> return r;
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index eec2f11..729fe05 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -113,6 +113,11 @@ static void vhost_init_is_le(struct vhost_virtqueue *vq)
> }
> #endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */
>
> +static inline int vhost_iotlb_hash(u64 iova)
> +{
> + return (iova >> PAGE_SHIFT) & (VHOST_IOTLB_SIZE - 1);
> +}
> +
> static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
> poll_table *pt)
> {
> @@ -384,8 +389,14 @@ void vhost_dev_init(struct vhost_dev *dev,
> dev->memory = NULL;
> dev->mm = NULL;
> spin_lock_init(&dev->work_lock);
> + spin_lock_init(&dev->iotlb_lock);
> + mutex_init(&dev->iotlb_req_mutex);
> INIT_LIST_HEAD(&dev->work_list);
> dev->worker = NULL;
> + dev->iotlb_request = NULL;
> + dev->iotlb_ctx = NULL;
> + dev->iotlb_file = NULL;
> + dev->pending_request.flags.type = VHOST_IOTLB_INVALIDATE;
>
> for (i = 0; i < dev->nvqs; ++i) {
> vq = dev->vqs[i];
> @@ -393,12 +404,17 @@ void vhost_dev_init(struct vhost_dev *dev,
> vq->indirect = NULL;
> vq->heads = NULL;
> vq->dev = dev;
> + vq->iotlb_request = NULL;
> mutex_init(&vq->mutex);
> vhost_vq_reset(dev, vq);
> if (vq->handle_kick)
> vhost_poll_init(&vq->poll, vq->handle_kick,
> POLLIN, dev);
> }
> +
> + init_completion(&dev->iotlb_completion);
> + for (i = 0; i < VHOST_IOTLB_SIZE; i++)
> + dev->iotlb[i].flags.valid = VHOST_IOTLB_INVALID;
> }
> EXPORT_SYMBOL_GPL(vhost_dev_init);
>
> @@ -940,9 +956,10 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> {
> struct file *eventfp, *filep = NULL;
> struct eventfd_ctx *ctx = NULL;
> + struct vhost_iotlb_entry entry;
> u64 p;
> long r;
> - int i, fd;
> + int index, i, fd;
>
> /* If you are not the owner, you can become one */
> if (ioctl == VHOST_SET_OWNER) {
> @@ -1008,6 +1025,80 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> if (filep)
> fput(filep);
> break;
> + case VHOST_SET_IOTLB_FD:
> + r = get_user(fd, (int __user *)argp);
> + if (r < 0)
> + break;
> + eventfp = fd == -1 ? NULL : eventfd_fget(fd);
> + if (IS_ERR(eventfp)) {
> + r = PTR_ERR(eventfp);
> + break;
> + }
> + if (eventfp != d->iotlb_file) {
> + filep = d->iotlb_file;
> + d->iotlb_file = eventfp;
> + ctx = d->iotlb_ctx;
> + d->iotlb_ctx = eventfp ?
> + eventfd_ctx_fileget(eventfp) : NULL;
> + } else
> + filep = eventfp;
> + for (i = 0; i < d->nvqs; ++i) {
> + mutex_lock(&d->vqs[i]->mutex);
> + d->vqs[i]->iotlb_ctx = d->iotlb_ctx;
> + mutex_unlock(&d->vqs[i]->mutex);
> + }
> + if (ctx)
> + eventfd_ctx_put(ctx);
> + if (filep)
> + fput(filep);
> + break;
> + case VHOST_SET_IOTLB_REQUEST_ENTRY:
> + if (!access_ok(VERIFY_READ, argp, sizeof(*d->iotlb_request)))
> + return -EFAULT;
> + if (!access_ok(VERIFY_WRITE, argp, sizeof(*d->iotlb_request)))
> + return -EFAULT;
> + d->iotlb_request = argp;
> + for (i = 0; i < d->nvqs; ++i) {
> + mutex_lock(&d->vqs[i]->mutex);
> + d->vqs[i]->iotlb_request = argp;
> + mutex_unlock(&d->vqs[i]->mutex);
> + }
> + break;
> + case VHOST_UPDATE_IOTLB:
> + r = copy_from_user(&entry, argp, sizeof(entry));
> + if (r < 0) {
> + r = -EFAULT;
> + goto done;
> + }
> +
> + index = vhost_iotlb_hash(entry.iova);
> +
> + spin_lock(&d->iotlb_lock);
> + switch (entry.flags.type) {
> + case VHOST_IOTLB_UPDATE:
> + d->iotlb[index] = entry;
> + break;
> + case VHOST_IOTLB_INVALIDATE:
> + if (d->iotlb[index].iova == entry.iova)
> + d->iotlb[index] = entry;
> + break;
> + default:
> + r = -EINVAL;
> + }
> + spin_unlock(&d->iotlb_lock);
> +
> + if (!r && entry.flags.type != VHOST_IOTLB_INVALIDATE) {
> + mutex_lock(&d->iotlb_req_mutex);
> + if (entry.iova == d->pending_request.iova &&
> + d->pending_request.flags.type ==
> + VHOST_IOTLB_MISS) {
> + d->pending_request = entry;
> + complete(&d->iotlb_completion);
> + }
> + mutex_unlock(&d->iotlb_req_mutex);
> + }
> +
> + break;
> default:
> r = -ENOIOCTLCMD;
> break;
> @@ -1177,9 +1268,104 @@ int vhost_init_used(struct vhost_virtqueue *vq)
> }
> EXPORT_SYMBOL_GPL(vhost_init_used);
>
> +static struct vhost_iotlb_entry vhost_iotlb_miss(struct vhost_virtqueue *vq,
> + u64 iova)
> +{
> + struct completion *c = &vq->dev->iotlb_completion;
> + struct vhost_iotlb_entry *pending = &vq->dev->pending_request;
> + struct vhost_iotlb_entry entry = {
> + .flags.valid = VHOST_IOTLB_INVALID,
> + };
> +
> + mutex_lock(&vq->dev->iotlb_req_mutex);
> +
> + if (!vq->iotlb_ctx)
> + goto err;
> +
> + if (!vq->dev->iotlb_request)
> + goto err;
> +
> + if (pending->flags.type == VHOST_IOTLB_MISS)
> + goto err;
> +
> + pending->iova = iova & PAGE_MASK;
> + pending->flags.type = VHOST_IOTLB_MISS;
> +
> + if (copy_to_user(vq->dev->iotlb_request, pending,
> + sizeof(struct vhost_iotlb_entry))) {
> + goto err;
> + }
> +
> + mutex_unlock(&vq->dev->iotlb_req_mutex);
> +
> + eventfd_signal(vq->iotlb_ctx, 1);
> + wait_for_completion_interruptible(c);
This can still be under vq lock, can it not?
Looks like this can cause deadlocks.
> +
> + mutex_lock(&vq->dev->iotlb_req_mutex);
> + entry = vq->dev->pending_request;
> + mutex_unlock(&vq->dev->iotlb_req_mutex);
> +
> + return entry;
> +err:
> + mutex_unlock(&vq->dev->iotlb_req_mutex);
> + return entry;
> +}
> +
> +static int translate_iotlb(struct vhost_virtqueue *vq, u64 iova, u32 len,
> + struct iovec iov[], int iov_size)
> +{
> + struct vhost_iotlb_entry *entry;
> + struct vhost_iotlb_entry miss;
> + struct vhost_dev *dev = vq->dev;
> + int ret = 0;
> + u64 s = 0, size;
> +
> + spin_lock(&dev->iotlb_lock);
> +
> + while ((u64) len > s) {
> + if (unlikely(ret >= iov_size)) {
> + ret = -ENOBUFS;
> + break;
> + }
> + entry = &vq->dev->iotlb[vhost_iotlb_hash(iova)];
> + if ((entry->iova != (iova & PAGE_MASK)) ||
> + (entry->flags.valid != VHOST_IOTLB_VALID)) {
> +
> + spin_unlock(&dev->iotlb_lock);
> + miss = vhost_iotlb_miss(vq, iova);
> + spin_lock(&dev->iotlb_lock);
> +
> + if (miss.flags.valid != VHOST_IOTLB_VALID ||
> + miss.iova != (iova & PAGE_MASK)) {
> + ret = -EFAULT;
> + goto err;
> + }
> + entry = &miss;
> + }
> +
> + if (entry->iova == (iova & PAGE_MASK)) {
> + size = entry->userspace_addr + entry->size - iova;
> + iov[ret].iov_base =
> + (void __user *)(entry->userspace_addr +
> + (iova & (PAGE_SIZE - 1)));
> + iov[ret].iov_len = min((u64)len - s, size);
> + s += size;
> + iova += size;
> + ret++;
> + } else {
> + BUG();
> + }
> + }
> +
> +err:
> + spin_unlock(&dev->iotlb_lock);
> + return ret;
> +}
> +
> static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
> struct iovec iov[], int iov_size)
> {
> +#if 0
> const struct vhost_memory_region *reg;
> struct vhost_memory *mem;
> struct iovec *_iov;
> @@ -1209,6 +1395,8 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
> }
>
> return ret;
> +#endif
> + return translate_iotlb(vq, addr, len, iov, iov_size);
> }
>
> /* Each buffer in the virtqueues is actually a chain of descriptors. This
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index d3f7674..d254efc 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -68,6 +68,8 @@ struct vhost_virtqueue {
> struct eventfd_ctx *call_ctx;
> struct eventfd_ctx *error_ctx;
> struct eventfd_ctx *log_ctx;
> + struct eventfd_ctx *iotlb_ctx;
> + struct vhost_iotlb __user *iotlb_request;
>
> struct vhost_poll poll;
>
> @@ -116,6 +118,8 @@ struct vhost_virtqueue {
> #endif
> };
>
> +#define VHOST_IOTLB_SIZE 1024
> +
> struct vhost_dev {
> struct vhost_memory *memory;
> struct mm_struct *mm;
> @@ -124,9 +128,18 @@ struct vhost_dev {
> int nvqs;
> struct file *log_file;
> struct eventfd_ctx *log_ctx;
> + struct file *iotlb_file;
> + struct eventfd_ctx *iotlb_ctx;
> + struct mutex iotlb_req_mutex;
> + struct vhost_iotlb_entry __user *iotlb_request;
> + struct vhost_iotlb_entry pending_request;
> + struct completion iotlb_completion;
> + struct vhost_iotlb_entry request;
> spinlock_t work_lock;
> struct list_head work_list;
> struct task_struct *worker;
> + spinlock_t iotlb_lock;
> + struct vhost_iotlb_entry iotlb[VHOST_IOTLB_SIZE];
> };
>
> void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs, int nvqs);
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index ab373191..400e513 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -63,6 +63,26 @@ struct vhost_memory {
> struct vhost_memory_region regions[0];
> };
>
> +struct vhost_iotlb_entry {
> + __u64 iova;
> + __u64 size;
> + __u64 userspace_addr;
> + struct {
> +#define VHOST_IOTLB_PERM_READ 0x1
> +#define VHOST_IOTLB_PERM_WRITE 0x10
> + __u8 perm;
> +#define VHOST_IOTLB_MISS 1
> +#define VHOST_IOTLB_UPDATE 2
> +#define VHOST_IOTLB_INVALIDATE 3
> + __u8 type;
> +#define VHOST_IOTLB_INVALID 0x1
> +#define VHOST_IOTLB_VALID 0x2
> + __u8 valid;
> + __u8 u8_padding;
> + __u32 padding;
> + } flags;
> +};
> +
> /* ioctls */
>
> #define VHOST_VIRTIO 0xAF
> @@ -127,6 +147,12 @@ struct vhost_memory {
> /* Set eventfd to signal an error */
> #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file)
>
> +/* IOTLB */
> +/* Specify an eventfd file descriptor to signle on IOTLB miss */
> +#define VHOST_SET_IOTLB_FD _IOW(VHOST_VIRTIO, 0x23, int)
> +#define VHOST_UPDATE_IOTLB _IOW(VHOST_VIRTIO, 0x24, struct vhost_iotlb_entry)
> +#define VHOST_SET_IOTLB_REQUEST_ENTRY _IOW(VHOST_VIRTIO, 0x25, struct vhost_iotlb_entry)
> +
> /* VHOST_NET specific defines */
>
> /* Attach virtio net ring to a raw socket, or tap device.
> --
> 2.5.0
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