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SubjectRe: [RFC PATCH] virtio: make sure legacy pci device gain 32bit-pfn vq
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在 2021/12/9 下午2:40, Michael S. Tsirkin 写道:
[snip]
>>>> 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
>
> Oh, if the device is virtual then I think you should just update it please.
> virtio 0.X is architecturally limited to small VMs,
> if your hypervisor supports more it should emulate virtio 1.0.

I see, nice to confirm the proper approach, although we don't have that
option on the desk :-P

So as long as we don't have any iommu enabled, the force dma approach
could be safe, is this correct?

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

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