On Sat, Sep 9, 2023 at 9:46 PM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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
>
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