From: Ankit Agrawal <ankita@xxxxxxxxxx> The VM_ALLOW_ANY_UNCACHED flag is implemented for ARM64, allowing KVM stage 2 device mapping attributes to use Normal-NC rather than DEVICE_nGnRE, which allows guest mappings supporting combining attributes (WC). ARM does not architecturally guarantee this is safe, and indeed some MMIO regions like the GICv2 VCPU interface can trigger uncontained faults if Normal-NC is used. To safely use VFIO in KVM the platform must guarantee full safety in the guest where no action taken against a MMIO mapping can trigger an uncontained failure. We belive that most VFIO PCI platforms support this for both mapping types, at least in common flows, based on some expectations of how PCI IP is integrated. So make vfio-pci set the VM_ALLOW_ANY_UNCACHED flag. Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx> Acked-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Signed-off-by: Ankit Agrawal <ankita@xxxxxxxxxx> --- drivers/vfio/pci/vfio_pci_core.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c index 1cbc990d42e0..c93bea18fc4b 100644 --- a/drivers/vfio/pci/vfio_pci_core.c +++ b/drivers/vfio/pci/vfio_pci_core.c @@ -1862,8 +1862,24 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma /* * See remap_pfn_range(), called from vfio_pci_fault() but we can't * change vm_flags within the fault handler. Set them now. + * + * VM_ALLOW_ANY_UNCACHED: The VMA flag is implemented for ARM64, + * allowing KVM stage 2 device mapping attributes to use Normal-NC + * rather than DEVICE_nGnRE, which allows guest mappings + * supporting combining attributes (WC). ARM does not + * architecturally guarantee this is safe, and indeed some MMIO + * regions like the GICv2 VCPU interface can trigger uncontained + * faults if Normal-NC is used. + * + * To safely use VFIO in KVM the platform must guarantee full + * safety in the guest where no action taken against a MMIO + * mapping can trigger an uncontained failure. We belive that + * most VFIO PCI platforms support this for both mapping types, + * at least in common flows, based on some expectations of how + * PCI IP is integrated. So set VM_ALLOW_ANY_UNCACHED in VMA flags. */ - vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); + vm_flags_set(vma, VM_ALLOW_ANY_UNCACHED | VM_IO | VM_PFNMAP | + VM_DONTEXPAND | VM_DONTDUMP); vma->vm_ops = &vfio_pci_mmap_ops; return 0; -- 2.34.1
