Messages in this thread | | | Date | Thu, 9 Dec 2021 16:26:47 +0800 | Subject | Re: [RFC PATCH] virtio: make sure legacy pci device gain 32bit-pfn vq | From | 王贇 <> |
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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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