On Tue, 18 Apr 2023 22:10:03 -0700, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Tue, Apr 18, 2023 at 02:18:52PM +0800, Xuan Zhuo wrote: > > Sorry, rethink about this, I think we maybe misunderstand something. > > > > First of all, let me give you a brief introduce of virtio device and pci device. > > If I make mistake, please point out. > > > > > > First, when one virtio pci device is probed, then the virtio pci driver will be > > called. Then we got one pci_device. > > Yes. > > > Then virtio_pci_probe will alloc one new device, and register it to virtio bus > > by register_virtio_device(). > > > > > > So here we have two device: pci-device and virtio-device. > > Yes. > > > If we call DMA API inside virtio, we use the pci-device. The virtio-device is > > not used for DMA API. > > Exactly. > > > Now we want to use the virtio-device to do direct dma. The virtio-device > > is created by virtio_pci_probe() of virtio pci driver. And register to virtio > > bus. So no firmware and not iommu and the bus is virtio bus, why we can not > > change the dma_ops of virtio-device? > > Because firmware doesn't know about your virtio-device. It is just a > made up Linux concept, and the IOMMU and firmware tables for it don't > know about it. DMA must only ever be done on actual physical > (including "physical" devices emulated by a hypervisor) devices, not > on devices made up by Linux. It's clear for me. Thanks. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
