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Message-ID: <fb3a6ad0-dc79-9b58-3a32-06e3145a4dad@huawei.com>
Date: Tue, 6 Dec 2022 16:45:42 +0800
From: "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)"
<longpeng2@...wei.com>
To: Jason Wang <jasowang@...hat.com>
CC: <stefanha@...hat.com>, <mst@...hat.com>, <sgarzare@...hat.com>,
<eperezma@...hat.com>, <cohuck@...hat.com>,
<arei.gonglei@...wei.com>, <yechuan@...wei.com>,
<huangzhichao@...wei.com>,
<virtualization@...ts.linux-foundation.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] vdpasim: support doorbell mapping
在 2022/12/6 14:59, Jason Wang 写道:
> On Mon, Dec 5, 2022 at 9:52 PM Longpeng(Mike) <longpeng2@...wei.com> wrote:
>>
>> From: Longpeng <longpeng2@...wei.com>
>>
>> Support doorbell mapping for vdpasim devices, then we can test the notify
>> passthrough feature even if there's no real hardware on hand.
>>
>> Allocates a dummy page which is used to emulate the notify page of the device,
>> all VQs share the same notify register that initiated to 0xffff. A periodic
>> work will check whether there're requests need to process ( the value of the
>> notify register is 0xffff or not ).
>>
>> This cap is disabled as default, users can enable it as follow:
>> modprobe vdpa_sim notify_passthrough=true
>>
>> Signed-off-by: Longpeng <longpeng2@...wei.com>
>> ---
>> Changes v1->v2:
>> - support both kick mode and passthrough mode. [Jason]
>> - poll the notify register first. [Jason, Michael]
>> ---
>> drivers/vdpa/vdpa_sim/vdpa_sim.c | 77 ++++++++++++++++++++++++++++++++
>> drivers/vdpa/vdpa_sim/vdpa_sim.h | 3 ++
>> 2 files changed, 80 insertions(+)
>>
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> index 7438a89ce939..07096a04dabb 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> @@ -14,6 +14,7 @@
>> #include <linux/slab.h>
>> #include <linux/sched.h>
>> #include <linux/dma-map-ops.h>
>> +#include <asm/set_memory.h>
>> #include <linux/vringh.h>
>> #include <linux/vdpa.h>
>> #include <linux/vhost_iotlb.h>
>> @@ -36,9 +37,16 @@ module_param(max_iotlb_entries, int, 0444);
>> MODULE_PARM_DESC(max_iotlb_entries,
>> "Maximum number of iotlb entries for each address space. 0 means unlimited. (default: 2048)");
>>
>> +static bool notify_passthrough;
>> +module_param(notify_passthrough, bool, 0444);
>> +MODULE_PARM_DESC(notify_passthrough,
>> + "Enable vq notify(doorbell) area mapping. (default: false)");
>
> I'm not sure if it's worth doing this, I think we can afford the cost
> of periodic work (especially considering it's a simulator).
>
We can support kick mode and passthgourh mode simultaneously now, it is
a little unnecessary. I would remove it in next version.
>> +
>> #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
>> #define VDPASIM_QUEUE_MAX 256
>> #define VDPASIM_VENDOR_ID 0
>> +#define VDPASIM_VRING_POLL_PERIOD 100 /* ms */
>> +#define VDPASIM_NOTIFY_DEFVAL 0xffff
>>
>> static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
>> {
>> @@ -246,6 +254,28 @@ static const struct dma_map_ops vdpasim_dma_ops = {
>> static const struct vdpa_config_ops vdpasim_config_ops;
>> static const struct vdpa_config_ops vdpasim_batch_config_ops;
>>
>> +static void vdpasim_notify_work(struct work_struct *work)
>> +{
>> + struct vdpasim *vdpasim;
>> + u16 *val;
>> +
>> + vdpasim = container_of(work, struct vdpasim, notify_work.work);
>> +
>> + if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
>> + goto out;
>> +
>> + if (!vdpasim->running)
>> + goto out;
>> +
>> + val = (u16 *)vdpasim->notify;
>> + if (xchg(val, VDPASIM_NOTIFY_DEFVAL) != VDPASIM_NOTIFY_DEFVAL)
>> + schedule_work(&vdpasim->work);
>> +
>> +out:
>> + schedule_delayed_work(&vdpasim->notify_work,
>> + msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
>> +}
>> +
>> struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>> const struct vdpa_dev_set_config *config)
>> {
>> @@ -287,6 +317,18 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>> set_dma_ops(dev, &vdpasim_dma_ops);
>> vdpasim->vdpa.mdev = dev_attr->mgmt_dev;
>>
>> + if (notify_passthrough) {
>> + INIT_DELAYED_WORK(&vdpasim->notify_work, vdpasim_notify_work);
>> +
>> + vdpasim->notify = __get_free_page(GFP_KERNEL | __GFP_ZERO);
>> + if (!vdpasim->notify)
>> + goto err_iommu;
>> +#ifdef CONFIG_X86
>> + set_memory_uc(vdpasim->notify, 1);
>> +#endif
>
> I had the same question with version 1, any reason for having this
> part uncacheable? It's a hint that we have bugs somewhere. Are we
> missing ACCESS/ORDER_PLATFORM or other features?
>
Oh, I had replied you in that thread.
The vm_page_prot of notify mapping VMA is pgprot_noncached (see
vhost_vdpa_fault) but the vdpasim->notify is WB, so we should set its
memtype to UC here and set it back to WB when releasing the device.
Otherwise, the warning in trace_pfn_remap() would be triggered.
For example:
x86/PAT: CPU 16/KVM:17819 map pfn RAM range req uncached-minus for [mem
0x5151f3000-0x5151f3fff], got write-back
>> + *(u16 *)vdpasim->notify = VDPASIM_NOTIFY_DEFVAL;
>
> WRITE_ONCE()?
>
Okay.
>> + }
>> +
>> vdpasim->config = kzalloc(dev_attr->config_size, GFP_KERNEL);
>> if (!vdpasim->config)
>> goto err_iommu;
>> @@ -495,6 +537,18 @@ static u8 vdpasim_get_status(struct vdpa_device *vdpa)
>> return status;
>> }
>>
>> +static void vdpasim_set_notify_work(struct vdpasim *vdpasim, bool start)
>> +{
>> + if (!notify_passthrough)
>> + return;
>
> Only two callers for this function: one is start another is stop. If
> we decide to get rid of notify_passthrough, I'd rather opencode the
> schedule/cancel_delayed().
>
Okay, thanks.
> Thanks
>
>> +
>> + if (start)
>> + schedule_delayed_work(&vdpasim->notify_work,
>> + msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
>> + else
>> + cancel_delayed_work_sync(&vdpasim->notify_work);
>> +}
>> +
>> static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
>> {
>> struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>> @@ -502,12 +556,14 @@ static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
>> spin_lock(&vdpasim->lock);
>> vdpasim->status = status;
>> spin_unlock(&vdpasim->lock);
>> + vdpasim_set_notify_work(vdpasim, status & VIRTIO_CONFIG_S_DRIVER_OK);
>> }
>>
>> static int vdpasim_reset(struct vdpa_device *vdpa, bool clear)
>> {
>> struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>
>> + vdpasim_set_notify_work(vdpasim, false);
>> spin_lock(&vdpasim->lock);
>> vdpasim->status = 0;
>> vdpasim_do_reset(vdpasim);
>> @@ -672,11 +728,24 @@ static int vdpasim_dma_unmap(struct vdpa_device *vdpa, unsigned int asid,
>> return 0;
>> }
>>
>> +static struct vdpa_notification_area
>> +vdpasim_get_vq_notification(struct vdpa_device *vdpa, u16 qid)
>> +{
>> + struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>> + struct vdpa_notification_area notify;
>> +
>> + notify.addr = virt_to_phys((void *)vdpasim->notify);
>> + notify.size = PAGE_SIZE;
>> +
>> + return notify;
>> +}
>> +
>> static void vdpasim_free(struct vdpa_device *vdpa)
>> {
>> struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>> int i;
>>
>> + vdpasim_set_notify_work(vdpasim, false);
>> cancel_work_sync(&vdpasim->work);
>>
>> for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
>> @@ -693,6 +762,12 @@ static void vdpasim_free(struct vdpa_device *vdpa)
>> vhost_iotlb_free(vdpasim->iommu);
>> kfree(vdpasim->vqs);
>> kfree(vdpasim->config);
>> + if (vdpasim->notify) {
>> +#ifdef CONFIG_X86
>> + set_memory_wb(vdpasim->notify, 1);
>> +#endif
>> + free_page(vdpasim->notify);
>> + }
>> }
>>
>> static const struct vdpa_config_ops vdpasim_config_ops = {
>> @@ -704,6 +779,7 @@ static const struct vdpa_config_ops vdpasim_config_ops = {
>> .get_vq_ready = vdpasim_get_vq_ready,
>> .set_vq_state = vdpasim_set_vq_state,
>> .get_vq_state = vdpasim_get_vq_state,
>> + .get_vq_notification = vdpasim_get_vq_notification,
>> .get_vq_align = vdpasim_get_vq_align,
>> .get_vq_group = vdpasim_get_vq_group,
>> .get_device_features = vdpasim_get_device_features,
>> @@ -737,6 +813,7 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops = {
>> .get_vq_ready = vdpasim_get_vq_ready,
>> .set_vq_state = vdpasim_set_vq_state,
>> .get_vq_state = vdpasim_get_vq_state,
>> + .get_vq_notification = vdpasim_get_vq_notification,
>> .get_vq_align = vdpasim_get_vq_align,
>> .get_vq_group = vdpasim_get_vq_group,
>> .get_device_features = vdpasim_get_device_features,
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> index 0e78737dcc16..0769ccbd3911 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> @@ -69,6 +69,9 @@ struct vdpasim {
>> bool running;
>> /* spinlock to synchronize iommu table */
>> spinlock_t iommu_lock;
>> + /* dummy notify page */
>> + unsigned long notify;
>> + struct delayed_work notify_work;
>> };
>>
>> struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *attr,
>> --
>> 2.23.0
>>
>
> .
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