vfio/type1: handle case where IOMMU does not support PAGE_SIZE size

Current vfio_pgsize_bitmap code hides the supported IOMMU page
sizes smaller than PAGE_SIZE. As a result, in case the IOMMU
does not support PAGE_SIZE page, the alignment check on map/unmap
is done with larger page sizes, if any. This can fail although
mapping could be done with pages smaller than PAGE_SIZE.

This patch modifies vfio_pgsize_bitmap implementation so that,
in case the IOMMU supports page sizes smaller than PAGE_SIZE
we pretend PAGE_SIZE is supported and hide sub-PAGE_SIZE sizes.
That way the user will be able to map/unmap buffers whose size/
start address is aligned with PAGE_SIZE. Pinning code uses that
granularity while iommu driver can use the sub-PAGE_SIZE size
to map the buffer.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 57d8c37a002b..59d47cb638d5 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -403,13 +403,26 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
 static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
 {
         struct vfio_domain *domain;
-        unsigned long bitmap = PAGE_MASK;
+        unsigned long bitmap = ULONG_MAX;
 
         mutex_lock(&iommu->lock);
         list_for_each_entry(domain, &iommu->domain_list, next)
                 bitmap &= domain->domain->ops->pgsize_bitmap;
         mutex_unlock(&iommu->lock);
 
+        /*
+         * In case the IOMMU supports page sizes smaller than PAGE_SIZE
+         * we pretend PAGE_SIZE is supported and hide sub-PAGE_SIZE sizes.
+         * That way the user will be able to map/unmap buffers whose size/
+         * start address is aligned with PAGE_SIZE. Pinning code uses that
+         * granularity while iommu driver can use the sub-PAGE_SIZE size
+         * to map the buffer.
+         */
+        if (bitmap & ~PAGE_MASK) {
+                bitmap &= PAGE_MASK;
+                bitmap |= PAGE_SIZE;
+        }
+
         return bitmap;
 }