For pass-through device assignment, the ARM64 KVM hypervisor retrieves the memory region properties physical address, size, and whether a region backed with struct page or not from VMA. The prefetchable attribute of a BAR region isn't visible to KVM to make an optimal decision for stage2 attributes. This patch updates vma->vm_page_prot and maps with write-combine attribute if the associated BAR is prefetchable. For ARM64 pgprot_writecombine() is mapped to memory-type MT_NORMAL_NC which has no side effects on reads and multiple writes can be combined. Signed-off-by: Shanker Donthineni <sdonthineni@xxxxxxxxxx> --- drivers/vfio/pci/vfio_pci.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c index 5023e23db3bc..1b734fe1dd51 100644 --- a/drivers/vfio/pci/vfio_pci.c +++ b/drivers/vfio/pci/vfio_pci.c @@ -1703,7 +1703,11 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma) } vma->vm_private_data = vdev; - vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); + if (IS_ENABLED(CONFIG_ARM64) && + (pci_resource_flags(pdev, index) & IORESOURCE_PREFETCH)) + vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot); + else + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); vma->vm_pgoff = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff; /* -- 2.17.1
