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Date: Thu, 3 Aug 2023 10:57:47 -0700
From: Si-Wei Liu <si-wei.liu@...cle.com>
To: Jason Wang <jasowang@...hat.com>,
Dragos Tatulea <dtatulea@...dia.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Gal Pressman <gal@...dia.com>, linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
Eugenio Pérez <eperezma@...hat.com>
Subject: Re: [PATCH 1/2] vdpa/mlx5: Fix mr->initialized semantics
On 8/3/2023 1:03 AM, Jason Wang wrote:
> On Thu, Aug 3, 2023 at 1:13 AM Dragos Tatulea <dtatulea@...dia.com> wrote:
>> The mr->initialized flag is shared between the control vq and data vq
>> part of the mr init/uninit. But if the control vq and data vq get placed
>> in different ASIDs, it can happen that initializing the control vq will
>> prevent the data vq mr from being initialized.
>>
>> This patch consolidates the control and data vq init parts into their
>> own init functions. The mr->initialized will now be used for the data vq
>> only. The control vq currently doesn't need a flag.
>>
>> The uninitializing part is also taken care of: mlx5_vdpa_destroy_mr got
>> split into data and control vq functions which are now also ASID aware.
>>
>> Fixes: 8fcd20c30704 ("vdpa/mlx5: Support different address spaces for control and data")
>> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
>> Reviewed-by: Eugenio Pérez <eperezma@...hat.com>
>> Reviewed-by: Gal Pressman <gal@...dia.com>
>> ---
>> drivers/vdpa/mlx5/core/mlx5_vdpa.h | 1 +
>> drivers/vdpa/mlx5/core/mr.c | 97 +++++++++++++++++++++---------
>> 2 files changed, 71 insertions(+), 27 deletions(-)
>>
>> diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>> index 25fc4120b618..a0420be5059f 100644
>> --- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>> +++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
>> @@ -31,6 +31,7 @@ struct mlx5_vdpa_mr {
>> struct list_head head;
>> unsigned long num_directs;
>> unsigned long num_klms;
>> + /* state of dvq mr */
>> bool initialized;
>>
>> /* serialize mkey creation and destruction */
>> diff --git a/drivers/vdpa/mlx5/core/mr.c b/drivers/vdpa/mlx5/core/mr.c
>> index 03e543229791..4ae14a248a4b 100644
>> --- a/drivers/vdpa/mlx5/core/mr.c
>> +++ b/drivers/vdpa/mlx5/core/mr.c
>> @@ -489,60 +489,103 @@ static void destroy_user_mr(struct mlx5_vdpa_dev *mvdev, struct mlx5_vdpa_mr *mr
>> }
>> }
>>
>> -void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev)
>> +static void _mlx5_vdpa_destroy_cvq_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
>> +{
>> + if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] != asid)
>> + return;
>> +
>> + prune_iotlb(mvdev);
>> +}
>> +
>> +static void _mlx5_vdpa_destroy_dvq_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
>> {
>> struct mlx5_vdpa_mr *mr = &mvdev->mr;
>>
>> - mutex_lock(&mr->mkey_mtx);
>> + if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
>> + return;
>> +
>> if (!mr->initialized)
>> - goto out;
>> + return;
>>
>> - prune_iotlb(mvdev);
>> if (mr->user_mr)
>> destroy_user_mr(mvdev, mr);
>> else
>> destroy_dma_mr(mvdev, mr);
>>
>> mr->initialized = false;
>> -out:
>> +}
>> +
>> +static void mlx5_vdpa_destroy_mr_asid(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
>> +{
>> + struct mlx5_vdpa_mr *mr = &mvdev->mr;
>> +
>> + mutex_lock(&mr->mkey_mtx);
>> +
>> + _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
>> + _mlx5_vdpa_destroy_cvq_mr(mvdev, asid);
>> +
>> mutex_unlock(&mr->mkey_mtx);
>> }
>>
>> -static int _mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev,
>> - struct vhost_iotlb *iotlb, unsigned int asid)
>> +void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev)
>> +{
>> + mlx5_vdpa_destroy_mr_asid(mvdev, mvdev->group2asid[MLX5_VDPA_CVQ_GROUP]);
>> + mlx5_vdpa_destroy_mr_asid(mvdev, mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP]);
>> +}
>> +
>> +static int _mlx5_vdpa_create_cvq_mr(struct mlx5_vdpa_dev *mvdev,
>> + struct vhost_iotlb *iotlb,
>> + unsigned int asid)
>> +{
>> + if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] != asid)
>> + return 0;
>> +
>> + return dup_iotlb(mvdev, iotlb);
> This worries me as conceptually, there should be no difference between
> dvq mr and cvq mr. The virtqueue should be loosely coupled with mr.
>
> One example is that, if we only do dup_iotlb() but not try to create
> dma mr here, we will break virtio-vdpa:
For this case, I guess we may need another way to support virtio-vdpa
1:1 mapping rather than overloading virtio device reset semantics, see:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg953755.html
> Conceptually, the address mapping is not a part of the abstraction for
> a virtio device now. So resetting the memory mapping during virtio
> device reset seems wrong.
where we want to keep memory mapping intact across virtio device reset
for best live migration latency/downtime. I wonder would it work to
reset the mapping in vhost-vdpa life cycle out of virtio reset, say
introduce a .reset_map() op to restore 1:1 mapping within
vhost_vdpa_remove_as() right after vhost_vdpa_iotlb_unmap()? Then we can
move the iotlb reset logic to there without worry breaking virtio-vdpa.
Thanks,
-Siwei
>
> commit 6f5312f801836e6af9bcbb0bdb44dc423e129206
> Author: Eli Cohen <elic@...dia.com>
> Date: Wed Jun 2 11:58:54 2021 +0300
>
> vdpa/mlx5: Add support for running with virtio_vdpa
>
> In order to support running vdpa using vritio_vdpa driver, we need to
> create a different kind of MR, one that has 1:1 mapping, since the
> addresses referring to virtqueues are dma addresses.
>
> We create the 1:1 MR in mlx5_vdpa_dev_add() only in case firmware
> supports the general capability umem_uid_0. The reason for that is that
> 1:1 MRs must be created with uid == 0 while virtqueue objects can be
> created with uid == 0 only when the firmware capability is on.
>
> If the set_map() callback is called with new translations provided
> through iotlb, the driver will destroy the 1:1 MR and create a regular
> one.
>
> Signed-off-by: Eli Cohen <elic@...dia.com>
> Link: https://lore.kernel.org/r/20210602085854.62690-1-elic@nvidia.com
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> Acked-by: Jason Wang <jasowang@...hat.com>
>
> Thanks
>
>
>> +}
>> +
>> +static int _mlx5_vdpa_create_dvq_mr(struct mlx5_vdpa_dev *mvdev,
>> + struct vhost_iotlb *iotlb,
>> + unsigned int asid)
>> {
>> struct mlx5_vdpa_mr *mr = &mvdev->mr;
>> int err;
>>
>> - if (mr->initialized)
>> + if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
>> return 0;
>>
>> - if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid) {
>> - if (iotlb)
>> - err = create_user_mr(mvdev, iotlb);
>> - else
>> - err = create_dma_mr(mvdev, mr);
>> + if (mr->initialized)
>> + return 0;
>>
>> - if (err)
>> - return err;
>> - }
>> + if (iotlb)
>> + err = create_user_mr(mvdev, iotlb);
>> + else
>> + err = create_dma_mr(mvdev, mr);
>>
>> - if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] == asid) {
>> - err = dup_iotlb(mvdev, iotlb);
>> - if (err)
>> - goto out_err;
>> - }
>> + if (err)
>> + return err;
>>
>> mr->initialized = true;
>> +
>> + return 0;
>> +}
>> +
>> +static int _mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev,
>> + struct vhost_iotlb *iotlb, unsigned int asid)
>> +{
>> + int err;
>> +
>> + err = _mlx5_vdpa_create_dvq_mr(mvdev, iotlb, asid);
>> + if (err)
>> + return err;
>> +
>> + err = _mlx5_vdpa_create_cvq_mr(mvdev, iotlb, asid);
>> + if (err)
>> + goto out_err;
>> +
>> return 0;
>>
>> out_err:
>> - if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid) {
>> - if (iotlb)
>> - destroy_user_mr(mvdev, mr);
>> - else
>> - destroy_dma_mr(mvdev, mr);
>> - }
>> + _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
>>
>> return err;
>> }
>> --
>> 2.41.0
>>
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