linux-kernel - Re: [PATCH RFC 04/12] vdpa: add vdpa simulator for block device

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Date:   Mon, 16 Nov 2020 11:17:03 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Laurent Vivier <lvivier@...hat.com>,
        linux-kernel@...r.kernel.org, Eli Cohen <elic@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>
Subject: Re: [PATCH RFC 04/12] vdpa: add vdpa simulator for block device

On Mon, Nov 16, 2020 at 12:10:19PM +0800, Jason Wang wrote:
>
>On 2020/11/13 下午9:47, Stefano Garzarella wrote:
>>From: Max Gurtovoy <mgurtovoy@...dia.com>
>>
>>This will allow running vDPA for virtio block protocol.
>>
>>Signed-off-by: Max Gurtovoy <mgurtovoy@...dia.com>
>>[sgarzare: various cleanups/fixes]
>>Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>>---
>>v1:
>>- Removed unused headers
>>- Used cpu_to_vdpasim*() to store config fields
>>- Replaced 'select VDPA_SIM' with 'depends on VDPA_SIM' since selected
>>   option can not depend on other [Jason]
>>- Start with a single queue for now [Jason]
>>- Add comments to memory barriers
>>---
>>  drivers/vdpa/vdpa_sim/vdpa_sim_blk.c | 124 +++++++++++++++++++++++++++
>>  drivers/vdpa/Kconfig                 |   9 ++
>>  drivers/vdpa/vdpa_sim/Makefile       |   1 +
>>  3 files changed, 134 insertions(+)
>>  create mode 100644 drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>>
>>diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>>new file mode 100644
>>index 000000000000..386dbb2f7138
>>--- /dev/null
>>+++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>>@@ -0,0 +1,124 @@
>>+// SPDX-License-Identifier: GPL-2.0-only
>>+/*
>>+ * VDPA simulator for block device.
>>+ *
>>+ * Copyright (c) 2020, Mellanox Technologies. All rights reserved.
>>+ *
>>+ */
>>+
>>+#include <linux/module.h>
>>+
>>+#include "vdpa_sim.h"
>>+
>>+#define VDPASIM_BLK_FEATURES	((1ULL << VIRTIO_BLK_F_SIZE_MAX) | \
>>+				 (1ULL << VIRTIO_BLK_F_SEG_MAX)  | \
>>+				 (1ULL << VIRTIO_BLK_F_BLK_SIZE) | \
>>+				 (1ULL << VIRTIO_BLK_F_TOPOLOGY) | \
>>+				 (1ULL << VIRTIO_BLK_F_MQ))
>>+
>>+#define VDPASIM_BLK_CAPACITY 0x40000
>>+#define VDPASIM_BLK_SIZE_MAX 0x1000
>>+#define VDPASIM_BLK_SEG_MAX 32
>>+#define VDPASIM_BLK_VQ_NUM 1
>>+
>>+static struct vdpasim *vdpasim_blk_dev;
>>+
>>+static void vdpasim_blk_work(struct work_struct *work)
>>+{
>>+	struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
>>+	u8 status = VIRTIO_BLK_S_OK;
>>+	int i;
>>+
>>+	spin_lock(&vdpasim->lock);
>>+
>>+	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
>>+		goto out;
>>+
>>+	for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
>>+		struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
>>+
>>+		if (!vq->ready)
>>+			continue;
>>+
>>+		while (vringh_getdesc_iotlb(&vq->vring, &vq->iov, &vq->iov,
>>+					    &vq->head, GFP_ATOMIC) > 0) {
>>+
>>+			int write;
>>+
>>+			vq->iov.i = vq->iov.used - 1;
>>+			write = vringh_iov_push_iotlb(&vq->vring, &vq->iov, &status, 1);
>>+			if (write <= 0)
>>+				break;
>>+
>>+			/* Make sure data is wrote before advancing index */
>>+			smp_wmb();
>>+
>>+			vringh_complete_iotlb(&vq->vring, vq->head, write);
>>+
>>+			/* Make sure used is visible before rasing the interrupt. */
>>+			smp_wmb();
>>+
>>+			if (vringh_need_notify_iotlb(&vq->vring) > 0)
>>+				vringh_notify(&vq->vring);
>
>
>Do we initialize vrh->notify anywhere? And This seems duplicated with 
>the following vq->cb.
>
>I think the correct way is to initialize vrh->notify and use 
>vringh_need_notify_iotlb()/vringh_notify() instead of the vq->cb here.

Okay, so I'll set vrh->notify in the vdpasim core with a function that 
calls vq->cb() (the callback set through .set_vq_cb).

>
>And while at it, it's better to convert net simulator to do the same.

Sure.

Thanks,
Stefano