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Message-ID: <20200628054940-mutt-send-email-mst@kernel.org>
Date: Sun, 28 Jun 2020 05:58:22 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, rob.miller@...adcom.com,
lingshan.zhu@...el.com, eperezma@...hat.com, lulu@...hat.com,
shahafs@...lanox.com, hanand@...inx.com, mhabets@...arflare.com,
gdawar@...inx.com, saugatm@...inx.com, vmireyno@...vell.com,
zhangweining@...jie.com.cn, eli@...lanox.com
Subject: Re: [PATCH RFC 4/5] vhost-vdpa: support IOTLB batching hints
On Thu, Jun 18, 2020 at 01:56:25PM +0800, Jason Wang wrote:
> This patches extend the vhost IOTLB API to accept batch updating hints
> form userspace. When userspace wants update the device IOTLB in a
> batch, it may do:
>
> 1) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_BEGIN flag
> 2) Perform a batch of IOTLB updating via VHOST_IOTLB_UPDATE/INVALIDATE
> 3) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_END flag
As long as we are extending the interface,
is there some way we could cut down the number of system calls needed
here?
>
> Vhost-vdpa may decide to batch the IOMMU/IOTLB updating in step 3 when
> vDPA device support set_map() ops. This is useful for the vDPA device
> that want to know all the mappings to tweak their own DMA translation
> logic.
>
> For vDPA device that doesn't require set_map(), no behavior changes.
>
> This capability is advertised via VHOST_BACKEND_F_IOTLB_BATCH capability.
>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> drivers/vhost/vdpa.c | 30 +++++++++++++++++++++++-------
> include/uapi/linux/vhost.h | 2 ++
> include/uapi/linux/vhost_types.h | 7 +++++++
> 3 files changed, 32 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 453057421f80..8f624bbafee7 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -56,7 +56,9 @@ enum {
> };
>
> enum {
> - VHOST_VDPA_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
> + VHOST_VDPA_BACKEND_FEATURES =
> + (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2) |
> + (1ULL << VHOST_BACKEND_F_IOTLB_BATCH),
> };
>
> /* Currently, only network backend w/o multiqueue is supported. */
> @@ -77,6 +79,7 @@ struct vhost_vdpa {
> int virtio_id;
> int minor;
> struct eventfd_ctx *config_ctx;
> + int in_batch;
> };
>
> static DEFINE_IDA(vhost_vdpa_ida);
> @@ -125,6 +128,7 @@ static void vhost_vdpa_reset(struct vhost_vdpa *v)
> const struct vdpa_config_ops *ops = vdpa->config;
>
> ops->set_status(vdpa, 0);
> + v->in_batch = 0;
> }
>
> static long vhost_vdpa_get_device_id(struct vhost_vdpa *v, u8 __user *argp)
> @@ -540,9 +544,10 @@ static int vhost_vdpa_map(struct vhost_vdpa *v,
>
> if (ops->dma_map)
> r = ops->dma_map(vdpa, iova, size, pa, perm);
> - else if (ops->set_map)
> - r = ops->set_map(vdpa, dev->iotlb);
> - else
> + else if (ops->set_map) {
> + if (!v->in_batch)
> + r = ops->set_map(vdpa, dev->iotlb);
> + } else
> r = iommu_map(v->domain, iova, pa, size,
> perm_to_iommu_flags(perm));
>
> @@ -559,9 +564,10 @@ static void vhost_vdpa_unmap(struct vhost_vdpa *v, u64 iova, u64 size)
>
> if (ops->dma_map)
> ops->dma_unmap(vdpa, iova, size);
> - else if (ops->set_map)
> - ops->set_map(vdpa, dev->iotlb);
> - else
> + else if (ops->set_map) {
> + if (!v->in_batch)
> + ops->set_map(vdpa, dev->iotlb);
> + } else
> iommu_unmap(v->domain, iova, size);
> }
>
> @@ -655,6 +661,8 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev,
> struct vhost_iotlb_msg *msg)
> {
> struct vhost_vdpa *v = container_of(dev, struct vhost_vdpa, vdev);
> + struct vdpa_device *vdpa = v->vdpa;
> + const struct vdpa_config_ops *ops = vdpa->config;
> int r = 0;
>
> r = vhost_dev_check_owner(dev);
> @@ -668,6 +676,14 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev,
> case VHOST_IOTLB_INVALIDATE:
> vhost_vdpa_unmap(v, msg->iova, msg->size);
> break;
> + case VHOST_IOTLB_BATCH_BEGIN:
> + v->in_batch = true;
> + break;
> + case VHOST_IOTLB_BATCH_END:
> + if (v->in_batch && ops->set_map)
> + ops->set_map(vdpa, dev->iotlb);
> + v->in_batch = false;
> + break;
> default:
> r = -EINVAL;
> break;
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index 0c2349612e77..565da96f55d5 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -91,6 +91,8 @@
>
> /* Use message type V2 */
> #define VHOST_BACKEND_F_IOTLB_MSG_V2 0x1
> +/* IOTLB can accpet batching hints */
typo
> +#define VHOST_BACKEND_F_IOTLB_BATCH 0x2
>
> #define VHOST_SET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x25, __u64)
> #define VHOST_GET_BACKEND_FEATURES _IOR(VHOST_VIRTIO, 0x26, __u64)
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index 669457ce5c48..5c12faffdde9 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -60,6 +60,13 @@ struct vhost_iotlb_msg {
> #define VHOST_IOTLB_UPDATE 2
> #define VHOST_IOTLB_INVALIDATE 3
> #define VHOST_IOTLB_ACCESS_FAIL 4
> +/* VHOST_IOTLB_BATCH_BEGIN is a hint that userspace will update
> + * several mappings afterwards. VHOST_IOTLB_BATCH_END is a hint that
> + * userspace had finished the mapping updating.
Well not just hints - in fact updates do not take place
until _END.
How about:
/* VHOST_IOTLB_BATCH_BEGIN and VHOST_IOTLB_BATCH_END allow modifying
* multiple mappings in one go: beginning with
* VHOST_IOTLB_BATCH_BEGIN, followed by any number of
VHOST_IOTLB_UPDATE messages, and ending with VHOST_IOTLB_BATCH_END.
*/
> When those two flags
> + * were set, kernel will ignore the rest fileds of the IOTLB message.
how about:
when one of these two values is used as the message type, the
rest of the fields in the message are ignored.
> + */
> +#define VHOST_IOTLB_BATCH_BEGIN 5
> +#define VHOST_IOTLB_BATCH_END 6
> __u8 type;
> };
>
> --
> 2.20.1
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