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Date: Mon, 30 Oct 2023 13:55:34 -0400
From: Steven Sistare <steven.sistare@...cle.com>
To: Eugenio Perez Martin <eperezma@...hat.com>
Cc: virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org,
"Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>, Eli Cohen <elic@...dia.com>,
Si-Wei Liu <si-wei.liu@...cle.com>,
Dragos Tatulea <dtatulea@...dia.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [RFC] vdpa/mlx5: preserve CVQ vringh index
On 10/30/2023 11:12 AM, Eugenio Perez Martin wrote:
> On Thu, Oct 26, 2023 at 10:09 PM Steve Sistare
> <steven.sistare@...cle.com> wrote:
>>
>> mlx5_vdpa does not preserve userland's view of vring base for the control
>> queue in the following sequence:
>>
>> ioctl VHOST_SET_VRING_BASE
>> ioctl VHOST_VDPA_SET_STATUS VIRTIO_CONFIG_S_DRIVER_OK
>> mlx5_vdpa_set_status()
>> setup_cvq_vring()
>> vringh_init_iotlb()
>> vringh_init_kern()
>> vrh->last_avail_idx = 0;
>> ioctl VHOST_GET_VRING_BASE
>>
>> To fix, restore the value of cvq->vring.last_avail_idx after calling
>> vringh_init_iotlb.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
>> ---
>> drivers/vdpa/mlx5/net/mlx5_vnet.c | 7 ++++++-
>> drivers/vhost/vringh.c | 30 ++++++++++++++++++++++++++++++
>> include/linux/vringh.h | 2 ++
>> 3 files changed, 38 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> index 946488b8989f..f64758143115 100644
>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> @@ -2795,13 +2795,18 @@ static int setup_cvq_vring(struct mlx5_vdpa_dev *mvdev)
>> struct mlx5_control_vq *cvq = &mvdev->cvq;
>> int err = 0;
>>
>> - if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ))
>> + if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)) {
>> + u16 last_avail_idx = cvq->vring.last_avail_idx;
>> +
>> err = vringh_init_iotlb(&cvq->vring, mvdev->actual_features,
>> MLX5_CVQ_MAX_ENT, false,
>> (struct vring_desc *)(uintptr_t)cvq->desc_addr,
>> (struct vring_avail *)(uintptr_t)cvq->driver_addr,
>> (struct vring_used *)(uintptr_t)cvq->device_addr);
>>
>> + if (!err)
>> + vringh_set_base_iotlb(&cvq->vring, last_avail_idx);
>> + }
>> return err;
>> }
>>
>> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
>> index 7b8fd977f71c..799762c83007 100644
>> --- a/drivers/vhost/vringh.c
>> +++ b/drivers/vhost/vringh.c
>> @@ -595,6 +595,24 @@ static inline void __vringh_notify_disable(struct vringh *vrh,
>> }
>> }
>>
>> +static inline int __vringh_set_base(struct vringh *vrh, u16 idx,
>> + int (*putu16)(const struct vringh *vrh,
>> + __virtio16 *p, u16 val))
>> +{
>> + int ret;
>> +
>> + ret = putu16(vrh, &vrh->vring.avail->idx, idx);
>> + if (ret)
>> + return ret;
>> +
>> + ret = putu16(vrh, &vrh->vring.used->idx, idx);
>> + if (ret)
>> + return ret;
>> +
>
> I don't think VMM should be able to modify the guest's vring memory.
> For vringh it should be enough with the next line, no need for
> previous.
>
> If I'm not wrong this was solved in the simulator by [1] and [2]. Am I
> missing something?
>
> Thanks!
>
> [1] https://lkml.org/lkml/2023/1/18/1045
> [2] https://www.spinics.net/lists/kernel/msg4705724.html
>
>> + vrh->last_avail_idx = vrh->last_used_idx = idx;
>> + return 0;
>> +}
>> +
OK, that makes sense. I just verified that the idx I pass to vringh_set_base_iotlb
does indeed match vrh->vring.avail->idx and vrh->vring.used->idx.
With no need to putu16, the fix could be confined to a few lines in the mlx5 driver:
setup_cvq_vring(struct mlx5_vdpa_dev *mvdev) {
idx = cvq->vring.last_avail_idx;
vringh_init_iotlb(&cvq->vring, ...);
cvq->vring.last_avail_idx = cvq->vring.last_used_idx = idx;
}
However, I wonder if re-syncing with the guest values would be a more robust fix:
setup_cvq_vring(struct mlx5_vdpa_dev *mvdev) {
vringh_init_iotlb(&cvq->vring, ...);
vringh_sync_iotlb(&cvq->vring);
}
vringh_sync_iotlb(struct vringh *vrh) {
getu16_iotlb(vrh, &vrh->last_avail_idx, &vrh->vring.avail->idx);
getu16_iotlb(vrh, &vrh->last_used_idx, &vrh->vring.used->idx);
}
- Steve
>> /* Userspace access helpers: in this case, addresses are really userspace. */
>> static inline int getu16_user(const struct vringh *vrh, u16 *val, const __virtio16 *p)
>> {
>> @@ -1456,6 +1474,18 @@ void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
>> }
>> EXPORT_SYMBOL(vringh_set_iotlb);
>>
>> +/**
>> + * vringh_set_base_iotlb - set avail_idx and used_idx
>> + * @vrh: the vring
>> + * @idx: the value to set
>> + */
>> +int vringh_set_base_iotlb(struct vringh *vrh, u16 idx)
>> +{
>> + return __vringh_set_base(vrh, idx, putu16_iotlb);
>> +}
>> +EXPORT_SYMBOL(vringh_set_base_iotlb);
>> +
>> +
>> /**
>> * vringh_getdesc_iotlb - get next available descriptor from ring with
>> * IOTLB.
>> diff --git a/include/linux/vringh.h b/include/linux/vringh.h
>> index c3a8117dabe8..e9b8af4e6a5e 100644
>> --- a/include/linux/vringh.h
>> +++ b/include/linux/vringh.h
>> @@ -306,6 +306,8 @@ int vringh_init_iotlb_va(struct vringh *vrh, u64 features,
>> struct vring_avail *avail,
>> struct vring_used *used);
>>
>> +int vringh_set_base_iotlb(struct vringh *vrh, u16 idx);
>> +
>> int vringh_getdesc_iotlb(struct vringh *vrh,
>> struct vringh_kiov *riov,
>> struct vringh_kiov *wiov,
>> --
>> 2.39.3
>>
>
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