On Fri, 23 May 2025 08:54:15 -0600, alex.williamson@xxxxxxxxxx wrote:
> > > +static long vpfn_pages(struct vfio_dma *dma,
> > > + dma_addr_t iova_start, long nr_pages)
> > > +{
> > > + dma_addr_t iova_end = iova_start + (nr_pages << PAGE_SHIFT);
> > > + struct vfio_pfn *vpfn;
> > > + long count = 0;
> > > +
> > > + do {
> > > + vpfn = vfio_find_vpfn_range(dma, iova_start, iova_end);
> >
> > I am somehow confused here. Function vfio_find_vpfn_range()is designed
> > to find, through the rbtree, the node that is closest to the root node
> > and satisfies the condition within the range [iova_start, iova_end),
> > rather than the node closest to iova_start? Or perhaps I have
> > misunderstood something?
>
> Sorry, that's an oversight on my part. We might forego the _range
> version and just do an inline walk of the tree counting the number of
> already accounted pfns within the range. Thanks,
>
> Alex
>
> > > + if (likely(!vpfn))
> > > + break;
> > > +
> > > + count++;
> > > + iova_start = vpfn->iova + PAGE_SIZE;
> > > + } while (iova_start < iova_end);
> > > +
> > > + return count;
> > > +}
The utilization of the function vpfn_pages() is undoubtedly a
good idea. It can swiftly determine the num of vpfn pages
within a specified range, which will evidently expedite the
process of vfio_pin_pages_remote(). Given that the function
vfio_find_vpfn_range() returns the "top" node in the rb tree
that satisfies the condition within the range
[iova_start, iova_end), might we consider implementing the
functionality of vpfn_pages() using the following approach?
+static long _vpfn_pages(struct vfio_pfn *vpfn,
+ dma_addr_t iova_start, dma_addr_t iova_end)
+{
+ struct vfio_pfn *left;
+ struct vfio_pfn *right;
+
+ if (!vpfn)
+ return 0;
+
+ left = vpfn->node.rb_left ?
+ rb_entry(vpfn->node.rb_left, struct vfio_pfn, node) : NULL;
+ right = vpfn->node.rb_right ?
+ rb_entry(vpfn->node.rb_right, struct vfio_pfn, node) : NULL;
+
+ if ((vpfn->iova >= iova_start) && (vpfn->iova < iova_end))
+ return 1 + _vpfn_pages(left, iova_start, iova_end) +
+ _vpfn_pages(right, iova_start, iova_end);
+
+ if (vpfn->iova >= iova_end)
+ return _vpfn_pages(left, iova_start, iova_end);
+
+ return _vpfn_pages(right, iova_start, iova_end);
+}
+
+static long vpfn_pages(struct vfio_dma *dma,
+ dma_addr_t iova_start, long nr_pages)
+{
+ dma_addr_t iova_end = iova_start + (nr_pages << PAGE_SHIFT);
+ struct vfio_pfn *top = vfio_find_vpfn_range(dma, iova_start, iova_end);
+
+ return _vpfn_pages(top, iova_start, iova_end);
+}
Thanks,
Zhe
