On 28/08/13 13:45, Laszlo Ersek wrote: > 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.
To be even more precise. This is only true for virtio-pci. virtio-ccw on s390x can define the queue address as 64bit. Christian
