[RFC PATCH v2 2/3] vfio-pci: Allow to mmap sub-page MMIO BARs if all MMIO BARs are page aligned

[Yongji Xie]

Current vfio-pci implementation disallows to mmap
sub-page(size < PAGE_SIZE) MMIO BARs because these BARs' mmio
page may be shared with other BARs.

But we should allow to mmap these sub-page MMIO BARs if PCI
resource allocator enforces the alignment of all MMIO BARs
to be at least PAGE_SIZE.

Signed-off-by: Yongji Xie <xyjxie at linux.vnet.ibm.com>
---
 drivers/vfio/pci/vfio_pci.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 7e9f497..09b3805 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -552,7 +552,8 @@ static long vfio_pci_ioctl(void *device_data,
 				     VFIO_REGION_INFO_FLAG_WRITE;
 			if (IS_ENABLED(CONFIG_VFIO_PCI_MMAP) &&
 			    pci_resource_flags(pdev, info.index) &
-			    IORESOURCE_MEM && info.size >= PAGE_SIZE) {
+			    IORESOURCE_MEM && (info.size >= PAGE_SIZE ||
+			    pci_resource_page_aligned)) {
 				info.flags |= VFIO_REGION_INFO_FLAG_MMAP;
 				if (info.index == vdev->msix_bar) {
 					ret = msix_sparse_mmap_cap(vdev, &caps);
@@ -954,6 +955,10 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
 		return -EINVAL;
 
 	phys_len = pci_resource_len(pdev, index);
+
+	if (pci_resource_page_aligned)
+		phys_len = PAGE_ALIGN(phys_len);
+
 	req_len = vma->vm_end - vma->vm_start;
 	pgoff = vma->vm_pgoff &
 		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
-- 
1.7.9.5