Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 2011-11-14 at 13:54 -0700, Alex Williamson wrote:
> On Fri, 2011-11-11 at 18:14 -0600, Scott Wood wrote:
> > On 11/03/2011 03:12 PM, Alex Williamson wrote: 
> > > +	for (i = 0; i < npage; i++, iova += PAGE_SIZE, vaddr += PAGE_SIZE) {
> > > +		unsigned long pfn = 0;
> > > +
> > > +		ret = vaddr_get_pfn(vaddr, rdwr, &pfn);
> > > +		if (ret) {
> > > +			__vfio_dma_unmap(iommu, start, i, rdwr);
> > > +			return ret;
> > > +		}
> > > +
> > > +		/* Only add actual locked pages to accounting */
> > > +		if (!is_invalid_reserved_pfn(pfn))
> > > +			locked++;
> > > +
> > > +		ret = iommu_map(iommu->domain, iova,
> > > +				(phys_addr_t)pfn << PAGE_SHIFT, 0, prot);
> > > +		if (ret) {
> > > +			/* Back out mappings on error */
> > > +			put_pfn(pfn, rdwr);
> > > +			__vfio_dma_unmap(iommu, start, i, rdwr);
> > > +			return ret;
> > > +		}
> > > +	}
> > 
> > There's no way to hand this stuff to the IOMMU driver in chunks larger
> > than a page?  That's going to be a problem for our IOMMU, which wants to
> > deal with large windows.
> 
> There is, this is just a simple implementation that maps individual
> pages.  We "just" need to determine physically contiguous chunks and
> mlock them instead of using get_user_pages.  The current implementation
> is much like how KVM maps iommu pages, but there shouldn't be a user API
> change to try to use larger chinks.  We want this for IOMMU large page
> support too.

Also, at one point intel-iommu didn't allow sub-ranges to be unmapped;
an unmap of a single page would unmap the entire original mapping that
contained that page.  That made it easier to map each page individually
for the flexibility it provided on unmap.  I need to see if we still
have that restriction.  Thanks,

Alex