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

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Message-Id: <200711122237.29369.amit.shah@qumranet.com>
Date:	Mon, 12 Nov 2007 22:37:29 +0530
From:	Amit Shah <amit.shah@...ranet.com>
To:	"Joerg Roedel" <joerg.roedel@....com>
Cc:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH 1/8] KVM: PVDMA Host: Handle reqeusts for guest DMA mappings

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.
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