On 08/28/13 11:22, Xie, Huawei wrote: > Hi Stefan: > I think you mention the descriptor address? I mean the vring PFN register. > /* A 32-bit r/w PFN for the currently selected queue */ > #define VIRTIO_PCI_QUEUE_PFN 8 > > And the linux driver sample code: > iowrite32(virt_to_phys(info->queue) >> VIRTIO_PCI_QUEUE_ADDR_SHIFT, > vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN); > > -----Original Message----- > From: Stefan Hajnoczi [mailto:stefa...@gmail.com] > Sent: Wednesday, August 28, 2013 4:07 PM > To: Xie, Huawei > Cc: qemu-devel@nongnu.org; ru...@rustcorp.com.au; Stefan Hajnoczi > Subject: Re: [Qemu-devel] Would virtio support 64 bit address for vring > virtqueue? > > On Wed, Aug 28, 2013 at 03:18:39AM +0000, Xie, Huawei wrote: >> I am developing virtio user space poll mode network driver. We allocate >> vring physical memory from huge page. On VMs with less than 4GB memory, it >> works well. But on VMs with like 8GB memory, huge page are all allocated >> from high end memory. >> So would virtio support 64bit address for vring virtqueue? > > The vring takes guest physical addresses and the C type is __u64 (see > /usr/include/linux/virtio_ring.h). 64-bit addresses are fine.
If you mean Queue Address field in the Virtio Header (section 2.2.2 in the virtio-0.9.5 specification), then please see 2.3 Virtqueue Configuration, step 3. You have to divide the guest-phys address by 4096 and store the quotient. The Queue Address field takes a page frame number, not a page frame address. This allows it to address up to 2^32 * 4096 == 16T bytes of RAM. Laszlo
