Re: [kvm-devel] [PATCH 1/8] KVM: PVDMA Host: Handle reqeusts for guest DMA mappings

Amit Shah
2007-11-12T17:14:43Z

On Monday 12 November 2007 21:25:22 Joerg Roedel wrote:
> On Wed, Nov 07, 2007 at 04:21:02PM +0200, Amit Shah wrote:
> > @@ -1649,6 +1913,15 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> > }
> >
> > switch (nr) {
> > + case KVM_PV_DMA_MAP:
> > + ret = pv_map_hypercall(vcpu, a0, a1);
> > + break;
> > + case KVM_PV_DMA_UNMAP:
> > + ret = pv_unmap_hypercall(vcpu, a0);
> > + break;
> > + case KVM_PV_PCI_DEVICE:
> > + ret = pv_mapped_pci_device_hypercall(vcpu, a0);
> > + break;
> > default:
> > ret = -KVM_ENOSYS;
> > break;
>
> How does synchronization work with that design? I don't see a hypercall
> to synchronize de DMA buffers. It will only work if GART is used as the
> dma_ops backend on the host side and not with SWIOTLB. But GART can be
> configured away. Or do I miss something?

A per-VM lock is needed while mapping or unmapping. It's one of the TODOs.