On Wed, 21 Mar 2018 03:30:29 +0000 "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > Sent: Wednesday, March 21, 2018 6:38 AM > > > > On Mon, 19 Mar 2018 07:51:58 +0000 > > "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > > > > > From: Shameer Kolothum > > > > Sent: Friday, March 16, 2018 12:35 AM > > > > > > > > This retrieves the reserved regions associated with dev group and > > > > checks for conflicts with any existing dma mappings. Also update > > > > the iova list excluding the reserved regions. > > > > > > > > Signed-off-by: Shameer Kolothum > > > > <shameerali.kolothum.thodi@xxxxxxxxxx> > > > > --- > > > > drivers/vfio/vfio_iommu_type1.c | 90 > > > > +++++++++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 90 insertions(+) > > > > > > > > diff --git a/drivers/vfio/vfio_iommu_type1.c > > > > b/drivers/vfio/vfio_iommu_type1.c > > > > index 1123c74..cfe2bb2 100644 > > > > --- a/drivers/vfio/vfio_iommu_type1.c > > > > +++ b/drivers/vfio/vfio_iommu_type1.c > > > > @@ -1313,6 +1313,82 @@ static int vfio_iommu_aper_resize(struct > > > > list_head *iova, > > > > return 0; > > > > } > > > > > > > > +/* > > > > + * Check reserved region conflicts with existing dma mappings > > > > + */ > > > > +static bool vfio_iommu_resv_conflict(struct vfio_iommu *iommu, > > > > + struct list_head *resv_regions) > > > > +{ > > > > + struct iommu_resv_region *region; > > > > + > > > > + /* Check for conflict with existing dma mappings */ > > > > + list_for_each_entry(region, resv_regions, list) { > > > > + if (vfio_find_dma(iommu, region->start, region->length)) > > > > + return true; > > > > + } > > > > + > > > > + return false; > > > > +} > > > > + > > > > +/* > > > > + * Check iova region overlap with reserved regions and > > > > + * exclude them from the iommu iova range > > > > + */ > > > > +static int vfio_iommu_resv_exclude(struct list_head *iova, > > > > + struct list_head *resv_regions) > > > > +{ > > > > + struct iommu_resv_region *resv; > > > > + struct vfio_iova *n, *next; > > > > + > > > > + list_for_each_entry(resv, resv_regions, list) { > > > > + phys_addr_t start, end; > > > > + > > > > + start = resv->start; > > > > + end = resv->start + resv->length - 1; > > > > + > > > > + list_for_each_entry_safe(n, next, iova, list) { > > > > + int ret = 0; > > > > + > > > > + /* No overlap */ > > > > + if ((start > n->end) || (end < n->start)) > > > > + continue; > > > > + /* > > > > + * Insert a new node if current node overlaps with > > > > the > > > > + * reserve region to exlude that from valid iova > > > > range. > > > > + * Note that, new node is inserted before the > > > > current > > > > + * node and finally the current node is deleted > > > > keeping > > > > + * the list updated and sorted. > > > > + */ > > > > + if (start > n->start) > > > > + ret = vfio_iommu_iova_insert(&n->list, > > > > + n->start, start - 1); > > > > + if (!ret && end < n->end) > > > > + ret = vfio_iommu_iova_insert(&n->list, > > > > + end + 1, n->end); > > > > + if (ret) > > > > + return ret; > > > > > > Is it safer to delete the 1st node here in case of failure of the 2nd node? > > > There is no problem with current logic since upon error iova_copy will > > > be released anyway. However this function alone doesn't assume the > > > fact of a temporary list, thus it's better to keep the list clean w/o garbage > > > left from any error handling. > > > > I don't think the proposal makes the list notably more sane on failure > > than we have here. If the function returns an error and the list is > > modified in any way, how can the caller recover? We're operating on a > > principle of modify a copy and throw it away on error, the only > > function level solution to the problem you're noting is to make each > > function generate a working copy, which is clearly inefficient. This > > is a static function, not intended for general use, so I think a > > sufficient approach to address your concern is to simply note the error > > behavior in the comment above the function, the list is in an > > unknown/inconsistent state on error. Thanks, > > > > 'static' doesn't mean it cannot be used for general purpose in the same > file. Obviously this is true, but expecting robust error handling, as might be found in an exported general purpose function, from a static specific purpose helper, is a bit absurd. The strategy is therefore, a) can we make it more general purpose without compromising the intent of the function; probably not without adding overhead of using a local copy of the list, b) can we modify the API, function name, arg names, etc to make the behavior more intuitive; maybe, c) Can we at least add a comment to make the potentially non-intuitive behavior obvious; of course. Thanks, Alex
