On Wed, 2010-06-30 at 21:30 -0700, Tom Lyon wrote:
> On Wednesday 30 June 2010 09:16:23 pm Alex Williamson wrote:
> > On Tue, 2010-06-08 at 14:21 -0700, Tom Lyon wrote:
> > > +int vfio_dma_unmap_dm(struct vfio_listener *listener, struct vfio_dma_map *dmp)
> > > +{
> > > + unsigned long start, npage;
> > > + struct dma_map_page *mlp;
> > > + struct list_head *pos, *pos2;
> > > + int ret;
> > > +
> > > + start = dmp->vaddr & ~PAGE_SIZE;
> > > + npage = dmp->size >> PAGE_SHIFT;
> > > +
> > > + ret = -ENXIO;
> > > + mutex_lock(&listener->vdev->dgate);
> > > + list_for_each_safe(pos, pos2, &listener->dm_list) {
> > > + mlp = list_entry(pos, struct dma_map_page, list);
> > > + if (dmp->vaddr != mlp->vaddr || mlp->npage != npage)
> > > + continue;
> > > + ret = 0;
> > > + vfio_dma_unmap(listener, mlp);
> > > + break;
> > > + }
> >
> > Hi Tom,
> >
> > Shouldn't we be matching the mlp based on daddr instead of vaddr? We
> > can have multiple dma address pointing at the same virtual address, so
> > dma address is the unique element. I'm also nervous about this dm_list.
> > For qemu device assignment, we're potentially statically mapping many GB
> > of iova space. It seems like this could get incredibly bloated and
> > slow. Thanks,
> >
> > Alex
>
> In weird circumstances, differing user vaddrs could reolve to the same physical address,
> so the uniqueness of any mapping is the <vaddr,len>.
That sounds like another argument for using daddr to me, no? There's
only one address space on the PCI bus, daddr. There's a 1:1 mapping of
daddr to physical page, but an N:1 mapping of vaddr to a physical page.
> Yes, a linear list is slow, but does qemu need a lot of mappings, or just big ones?
I'm not sure yet, the first interface I tried seems to be giving me
handfuls of pages. We sometimes reprogram the guest physical address
(daddr) to a new virtual address (vaddr), but I don't know what the old
virtual address was, so I can't unmap it. That's when I ran into the
issue above. Thanks,
Alex
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