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

[王贇 <yun.wang@linux.alibaba.com>]

在 2021/12/8 下午3:23, Michael S. Tsirkin 写道:
> On Tue, Dec 07, 2021 at 05:09:56PM +0800, 王贇 wrote:
>>
>>
>> 在 2021/12/7 下午4:13, Michael S. Tsirkin 写道:
>>> On Tue, Dec 07, 2021 at 03:51:45PM +0800, 王贇 wrote:
>>>> We observed issues like:
>>>>     virtio-pci 0000:14:00.0: platform bug: legacy virtio-mmio must
>>>>     not be used with RAM above 0x4000GB
>>>>
>>>> when we have a legacy pci device which desired 32bit-pfn vq
>>>> but gain 64bit-pfn instead, lead into the failure of probe.
>>>>
>>>> vring_use_dma_api() is playing the key role in here, to help the
>>>> allocation process understand which kind of vq it should alloc,
>>>> however, it failed to take care the legacy pci device, which only
>>>> have 32bit feature flag and can never have VIRTIO_F_ACCESS_PLATFORM
>>>> setted.
>>>>
>>>> This patch introduce force_dma flag to help vring_use_dma_api()
>>>> understanding the requirement better, to avoid the failing.
>>>>
>>>> Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com>
>>>
>>> This will break configs where the device appears behind
>>> a virtual iommu, so this won't fly.
>>> Just make your device support 1.0, eh?
>>
>> 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 :-)

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

> 
> 
>>>
>>>> ---
>>>>    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