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Si-Wei Liu

2023-Sep-09 13:43 UTC

[PATCH RFC v3 4/4] vhost-vdpa: introduce IOTLB_PERSIST backend feature bit

Userspace needs this feature flag to distinguish if vhost-vdpa
iotlb in the kernel supports persistent IOTLB mapping across
device reset. There are two cases that backend may claim
this feature bit on:

- parent device that has to work with platform IOMMU
- parent device with on-chip IOMMU that has the expected
  .reset_map support in driver

Signed-off-by: Si-Wei Liu <si-wei.liu at oracle.com>
---
RFC v2 -> v3:
  - fix missing return due to merge error

---
 drivers/vhost/vdpa.c             | 16 +++++++++++++++-
 include/uapi/linux/vhost_types.h |  2 ++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 71fbd559..b404504 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -414,6 +414,14 @@ static bool vhost_vdpa_has_desc_group(const struct
vhost_vdpa *v)
 	return ops->get_vq_desc_group;
 }
 
+static bool vhost_vdpa_has_persistent_map(const struct vhost_vdpa *v)
+{
+	struct vdpa_device *vdpa = v->vdpa;
+	const struct vdpa_config_ops *ops = vdpa->config;
+
+	return (!ops->set_map && !ops->dma_map) || ops->reset_map;
+}
+
 static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
 {
 	struct vdpa_device *vdpa = v->vdpa;
@@ -716,7 +724,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 		if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
 				 BIT_ULL(VHOST_BACKEND_F_DESC_ASID) |
 				 BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
-				 BIT_ULL(VHOST_BACKEND_F_RESUME)))
+				 BIT_ULL(VHOST_BACKEND_F_RESUME) |
+				 BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST)))
 			return -EOPNOTSUPP;
 		if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
 		     !vhost_vdpa_can_suspend(v))
@@ -730,6 +739,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 		if ((features & BIT_ULL(VHOST_BACKEND_F_DESC_ASID)) &&
 		     !vhost_vdpa_has_desc_group(v))
 			return -EOPNOTSUPP;
+		if ((features & BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST)) &&
+		     !vhost_vdpa_has_persistent_map(v))
+			return -EOPNOTSUPP;
 		vhost_set_backend_features(&v->vdev, features);
 		return 0;
 	}
@@ -785,6 +797,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 			features |= BIT_ULL(VHOST_BACKEND_F_RESUME);
 		if (vhost_vdpa_has_desc_group(v))
 			features |= BIT_ULL(VHOST_BACKEND_F_DESC_ASID);
+		if (vhost_vdpa_has_persistent_map(v))
+			features |= BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST);
 		if (copy_to_user(featurep, &features, sizeof(features)))
 			r = -EFAULT;
 		break;
diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
index 6acc604..0fdb6f0 100644
--- a/include/uapi/linux/vhost_types.h
+++ b/include/uapi/linux/vhost_types.h
@@ -186,5 +186,7 @@ struct vhost_vdpa_iova_range {
  * buffers may reside. Requires VHOST_BACKEND_F_IOTLB_ASID.
  */
 #define VHOST_BACKEND_F_DESC_ASID    0x6
+/* IOTLB don't flush memory mapping across device reset */
+#define VHOST_BACKEND_F_IOTLB_PERSIST  0x7
 
 #endif
-- 
1.8.3.1

Jason Wang

2023-Sep-11 03:52 UTC

head link

[PATCH RFC v3 4/4] vhost-vdpa: introduce IOTLB_PERSIST backend feature bit

On Sat, Sep 9, 2023 at 9:46?PM Si-Wei Liu <si-wei.liu at oracle.com>
wrote:>
> Userspace needs this feature flag to distinguish if vhost-vdpa
> iotlb in the kernel supports persistent IOTLB mapping across
> device reset.
As discussed, the IOTLB persists for devices with platform IOMMU at
least. You've mentioned that this behaviour is covered by Qemu since
it reset IOTLB on reset. I wonder what happens if we simply decouple
the IOTLB reset from vDPA reset in Qemu. Could we meet bugs there?

Btw, is there a Qemu patch for reference for this new feature?

Thanks
> There are two cases that backend may claim
> this feature bit on:
>
> - parent device that has to work with platform IOMMU
> - parent device with on-chip IOMMU that has the expected
>   .reset_map support in driver
>
> Signed-off-by: Si-Wei Liu <si-wei.liu at oracle.com>
> ---
> RFC v2 -> v3:
>   - fix missing return due to merge error
>
> ---
>  drivers/vhost/vdpa.c             | 16 +++++++++++++++-
>  include/uapi/linux/vhost_types.h |  2 ++
>  2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 71fbd559..b404504 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -414,6 +414,14 @@ static bool vhost_vdpa_has_desc_group(const struct
vhost_vdpa *v)
>         return ops->get_vq_desc_group;
>  }
>
> +static bool vhost_vdpa_has_persistent_map(const struct vhost_vdpa *v)
> +{
> +       struct vdpa_device *vdpa = v->vdpa;
> +       const struct vdpa_config_ops *ops = vdpa->config;
> +
> +       return (!ops->set_map && !ops->dma_map) ||
ops->reset_map;
> +}
> +
>  static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user
*featurep)
>  {
>         struct vdpa_device *vdpa = v->vdpa;
> @@ -716,7 +724,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file
*filep,
>                 if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
>                                  BIT_ULL(VHOST_BACKEND_F_DESC_ASID) |
>                                  BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
> -                                BIT_ULL(VHOST_BACKEND_F_RESUME)))
> +                                BIT_ULL(VHOST_BACKEND_F_RESUME) |
> +                                BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST)))
>                         return -EOPNOTSUPP;
>                 if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND))
&&
>                      !vhost_vdpa_can_suspend(v))
> @@ -730,6 +739,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file
*filep,
>                 if ((features & BIT_ULL(VHOST_BACKEND_F_DESC_ASID))
&&
>                      !vhost_vdpa_has_desc_group(v))
>                         return -EOPNOTSUPP;
> +               if ((features & BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST))
&&
> +                    !vhost_vdpa_has_persistent_map(v))
> +                       return -EOPNOTSUPP;
>                 vhost_set_backend_features(&v->vdev, features);
>                 return 0;
>         }
> @@ -785,6 +797,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file
*filep,
>                         features |= BIT_ULL(VHOST_BACKEND_F_RESUME);
>                 if (vhost_vdpa_has_desc_group(v))
>                         features |= BIT_ULL(VHOST_BACKEND_F_DESC_ASID);
> +               if (vhost_vdpa_has_persistent_map(v))
> +                       features |= BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST);
>                 if (copy_to_user(featurep, &features,
sizeof(features)))
>                         r = -EFAULT;
>                 break;
> diff --git a/include/uapi/linux/vhost_types.h
b/include/uapi/linux/vhost_types.h
> index 6acc604..0fdb6f0 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -186,5 +186,7 @@ struct vhost_vdpa_iova_range {
>   * buffers may reside. Requires VHOST_BACKEND_F_IOTLB_ASID.
>   */
>  #define VHOST_BACKEND_F_DESC_ASID    0x6
> +/* IOTLB don't flush memory mapping across device reset */
> +#define VHOST_BACKEND_F_IOTLB_PERSIST  0x7
>
>  #endif
> --
> 1.8.3.1
>

Linux Virtualization - Sep 2023 - [PATCH RFC v3 4/4] vhost-vdpa: introduce IOTLB_PERSIST backend feature bit

[PATCH RFC v3 4/4] vhost-vdpa: introduce IOTLB_PERSIST backend feature bit

[PATCH RFC v3 4/4] vhost-vdpa: introduce IOTLB_PERSIST backend feature bit