linux-kernel - Re: [RFC PATCH] virtio: make sure legacy pci device gain 32bit-pfn vq

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Date:   Thu, 9 Dec 2021 11:21:36 +0800
From:   王贇 <yun.wang@...ux.alibaba.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        "open list:VIRTIO CORE AND NET DRIVERS" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] virtio: make sure legacy pci device gain 32bit-pfn vq



在 2021/12/8 下午7:08, Michael S. Tsirkin 写道:
[snip]
>>>>
>>>> Hi, Michael
>>>>
>>>> Thanks for the comment, unfortunately modify device is not an option for us
>>>> :-(
>>>>
>>>> Is there any idea on how to solve this issue properly?
>>>>
>>>> Regards,
>>>> Michael Wang
>>>
>>> By the way, there is a bug in the error message. Want to fix that?
>>
>> Could you please provide more detail about the bug? We'd like to help fixing
>> it :-)
> 
> virtio-pci 0000:14:00.0: platform bug: legacy virtio-mmio must ...
> 
> should be virtio-pci not virtio-mmio

Patch on the way~

> 
> 
> 
>> Besides, I've checked that patch but it can't address our issue, we actually
>> have this legacy pci device on arm platform, and the memory layout is
>> unfriendly since allocation rarely providing page-address below 44bit, we
>> understand the virtio-iommu case should not do force dma, while we don't
>> have that so it's just working fine.
>>
>> Regards,
>> Michael Wang
> 
> Hmm wait a sec is it a physical device or a hypervisor?
> If a physical one then doesn't it need VIRTIO_F_ORDER_PLATFORM
> on ARM?

The PCI device is virtual, I can't see how VIRTIO_F_ORDER_PLATFORM help 
address this issue, legacy pci config is 32bit but it's 36, seems like 
will never be included?

Regards,
Michael Wang

> 
> 
> 
>>>
>>>
>>>>>
>>>>>> ---
>>>>>>     drivers/virtio/virtio_pci_legacy.c | 10 ++++++++++
>>>>>>     drivers/virtio/virtio_ring.c       |  3 +++
>>>>>>     include/linux/virtio.h             |  1 +
>>>>>>     3 files changed, 14 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/virtio/virtio_pci_legacy.c
>>>>>> b/drivers/virtio/virtio_pci_legacy.c
>>>>>> index d62e983..11f2ebf 100644
>>>>>> --- a/drivers/virtio/virtio_pci_legacy.c
>>>>>> +++ b/drivers/virtio/virtio_pci_legacy.c
>>>>>> @@ -263,6 +263,16 @@ int virtio_pci_legacy_probe(struct virtio_pci_device
>>>>>> *vp_dev)
>>>>>>     	vp_dev->setup_vq = setup_vq;
>>>>>>     	vp_dev->del_vq = del_vq;
>>>>>>
>>>>>> +	/*
>>>>>> +	 * The legacy pci device requre 32bit-pfn vq,
>>>>>> +	 * or setup_vq() will failed.
>>>>>> +	 *
>>>>>> +	 * Thus we make sure vring_use_dma_api() will
>>>>>> +	 * return true during the allocation by marking
>>>>>> +	 * force_dma here.
>>>>>> +	 */
>>>>>> +	vp_dev->vdev.force_dma = true;
>>>>>> +
>>>>>>     	return 0;
>>>>>>
>>>>>>     err_iomap:
>>>>>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>>>>>> index 3035bb6..6562e01 100644
>>>>>> --- a/drivers/virtio/virtio_ring.c
>>>>>> +++ b/drivers/virtio/virtio_ring.c
>>>>>> @@ -245,6 +245,9 @@ static inline bool virtqueue_use_indirect(struct
>>>>>> virtqueue *_vq,
>>>>>>
>>>>>>     static bool vring_use_dma_api(struct virtio_device *vdev)
>>>>>>     {
>>>>>> +	if (vdev->force_dma)
>>>>>> +		return true;
>>>>>> +
>>>>>>     	if (!virtio_has_dma_quirk(vdev))
>>>>>>     		return true;
>>>>>>
>>>>>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>>>>>> index 41edbc0..a4eb29d 100644
>>>>>> --- a/include/linux/virtio.h
>>>>>> +++ b/include/linux/virtio.h
>>>>>> @@ -109,6 +109,7 @@ struct virtio_device {
>>>>>>     	bool failed;
>>>>>>     	bool config_enabled;
>>>>>>     	bool config_change_pending;
>>>>>> +	bool force_dma;
>>>>>>     	spinlock_t config_lock;
>>>>>>     	spinlock_t vqs_list_lock; /* Protects VQs list access */
>>>>>>     	struct device dev;
>>>>>> -- 
>>>>>> 1.8.3.1