Re: [PATCH V2 vfio 5/9] virtio-pci: Initialize the supported admin commands

[Yishai Hadas via Virtualization <virtualization@lists.linux-foundation.org>]

On 30/10/2023 17:57, Michael S. Tsirkin wrote:
> On Mon, Oct 30, 2023 at 05:27:50PM +0200, Yishai Hadas wrote:
>> On 29/10/2023 22:17, Michael S. Tsirkin wrote:
>>> On Sun, Oct 29, 2023 at 05:59:48PM +0200, Yishai Hadas wrote:
>>>> Initialize the supported admin commands upon activating the admin queue.
>>>>
>>>> The supported commands are saved as part of the admin queue context, it
>>>> will be used by the next patches from this series.
>>>>
>>>> Note:
>>>> As we don't want to let upper layers to execute admin commands before
>>>> that this initialization step was completed, we set ref count to 1 only
>>>> post of that flow and use a non ref counted version command for this
>>>> internal flow.
>>>>
>>>> Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
>>>> ---
>>>>    drivers/virtio/virtio_pci_common.h |  1 +
>>>>    drivers/virtio/virtio_pci_modern.c | 77 +++++++++++++++++++++++++++++-
>>>>    2 files changed, 77 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
>>>> index a21b9ba01a60..9e07e556a51a 100644
>>>> --- a/drivers/virtio/virtio_pci_common.h
>>>> +++ b/drivers/virtio/virtio_pci_common.h
>>>> @@ -46,6 +46,7 @@ struct virtio_pci_admin_vq {
>>>>    	struct virtio_pci_vq_info info;
>>>>    	struct completion flush_done;
>>>>    	refcount_t refcount;
>>>> +	u64 supported_cmds;
>>>>    	/* Name of the admin queue: avq.$index. */
>>>>    	char name[10];
>>>>    	u16 vq_index;
>>>> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
>>>> index ccd7a4d9f57f..25e27aa79cab 100644
>>>> --- a/drivers/virtio/virtio_pci_modern.c
>>>> +++ b/drivers/virtio/virtio_pci_modern.c
>>>> @@ -19,6 +19,9 @@
>>>>    #define VIRTIO_RING_NO_LEGACY
>>>>    #include "virtio_pci_common.h"
>>>> +static int vp_modern_admin_cmd_exec(struct virtio_device *vdev,
>>>> +				    struct virtio_admin_cmd *cmd);
>>>> +
>>> I don't much like forward declarations. Just order functions sensibly
>>> and they will not be needed.
>> OK, will be part of V3.
>>
>>>>    static u64 vp_get_features(struct virtio_device *vdev)
>>>>    {
>>>>    	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
>>>> @@ -59,6 +62,42 @@ vp_modern_avq_set_abort(struct virtio_pci_admin_vq *admin_vq, bool abort)
>>>>    	WRITE_ONCE(admin_vq->abort, abort);
>>>>    }
>>>> +static void virtio_pci_admin_init_cmd_list(struct virtio_device *virtio_dev)
>>>> +{
>>>> +	struct virtio_pci_device *vp_dev = to_vp_device(virtio_dev);
>>>> +	struct virtio_admin_cmd cmd = {};
>>>> +	struct scatterlist result_sg;
>>>> +	struct scatterlist data_sg;
>>>> +	__le64 *data;
>>>> +	int ret;
>>>> +
>>>> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
>>>> +	if (!data)
>>>> +		return;
>>>> +
>>>> +	sg_init_one(&result_sg, data, sizeof(*data));
>>>> +	cmd.opcode = cpu_to_le16(VIRTIO_ADMIN_CMD_LIST_QUERY);
>>>> +	cmd.group_type = cpu_to_le16(VIRTIO_ADMIN_GROUP_TYPE_SRIOV);
>>>> +	cmd.result_sg = &result_sg;
>>>> +
>>>> +	ret = vp_modern_admin_cmd_exec(virtio_dev, &cmd);
>>>> +	if (ret)
>>>> +		goto end;
>>>> +
>>>> +	sg_init_one(&data_sg, data, sizeof(*data));
>>>> +	cmd.opcode = cpu_to_le16(VIRTIO_ADMIN_CMD_LIST_USE);
>>>> +	cmd.data_sg = &data_sg;
>>>> +	cmd.result_sg = NULL;
>>>> +
>>>> +	ret = vp_modern_admin_cmd_exec(virtio_dev, &cmd);
>>>> +	if (ret)
>>>> +		goto end;
>>>> +
>>>> +	vp_dev->admin_vq.supported_cmds = le64_to_cpu(*data);
>>>> +end:
>>>> +	kfree(data);
>>>> +}
>>>> +
>>>>    static void vp_modern_avq_activate(struct virtio_device *vdev)
>>>>    {
>>>>    	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
>>>> @@ -67,6 +106,7 @@ static void vp_modern_avq_activate(struct virtio_device *vdev)
>>>>    	if (!virtio_has_feature(vdev, VIRTIO_F_ADMIN_VQ))
>>>>    		return;
>>>> +	virtio_pci_admin_init_cmd_list(vdev);
>>>>    	init_completion(&admin_vq->flush_done);
>>>>    	refcount_set(&admin_vq->refcount, 1);
>>>>    	vp_modern_avq_set_abort(admin_vq, false);
>>>> @@ -562,6 +602,35 @@ static bool vp_get_shm_region(struct virtio_device *vdev,
>>>>    	return true;
>>>>    }
>>>> +static int __virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq,
>>>> +				    struct scatterlist **sgs,
>>>> +				    unsigned int out_num,
>>>> +				    unsigned int in_num,
>>>> +				    void *data,
>>>> +				    gfp_t gfp)
>>>> +{
>>>> +	struct virtqueue *vq;
>>>> +	int ret, len;
>>>> +
>>>> +	vq = admin_vq->info.vq;
>>>> +
>>>> +	ret = virtqueue_add_sgs(vq, sgs, out_num, in_num, data, gfp);
>>>> +	if (ret < 0)
>>>> +		return ret;
>>>> +
>>>> +	if (unlikely(!virtqueue_kick(vq)))
>>>> +		return -EIO;
>>>> +
>>>> +	while (!virtqueue_get_buf(vq, &len) &&
>>>> +	       !virtqueue_is_broken(vq))
>>>> +		cpu_relax();
>>>> +
>>>> +	if (virtqueue_is_broken(vq))
>>>> +		return -EIO;
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>> This is tolerable I guess but it might pin the CPU for a long time.
>>> The difficulty is handling suprize removal well which we currently
>>> don't do with interrupts. I would say it's ok as is but add
>>> a TODO comments along the lines of /* TODO: use interrupts once these virtqueue_is_broken */
>> I assume that you asked for adding the below comment before the while loop:
>> /* TODO use interrupts to reduce cpu cycles in the future */
>>
>> Right ?
>>
>> Yishai
> Well I wrote what I meant. in the future is redundant - everyone knows
> we can't change the past.

I agree, no need for 'in the future'.

However, in your suggestion you mentioned  "once these virtqueue_is_broken".

What does that mean in current polling mode ?

Yishai

>
>>>>    static int virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq,
>>>>    				    struct scatterlist **sgs,
>>>>    				    unsigned int out_num,
>>>> @@ -653,7 +722,13 @@ static int vp_modern_admin_cmd_exec(struct virtio_device *vdev,
>>>>    		in_num++;
>>>>    	}
>>>> -	ret = virtqueue_exec_admin_cmd(&vp_dev->admin_vq, sgs,
>>>> +	if (cmd->opcode == VIRTIO_ADMIN_CMD_LIST_QUERY ||
>>>> +	    cmd->opcode == VIRTIO_ADMIN_CMD_LIST_USE)
>>>> +		ret = __virtqueue_exec_admin_cmd(&vp_dev->admin_vq, sgs,
>>>> +				       out_num, in_num,
>>>> +				       sgs, GFP_KERNEL);
>>>> +	else
>>>> +		ret = virtqueue_exec_admin_cmd(&vp_dev->admin_vq, sgs,
>>>>    				       out_num, in_num,
>>>>    				       sgs, GFP_KERNEL);
>>>>    	if (ret) {
>>>> -- 
>>>> 2.27.0


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