Merge tag 'kvmarm-6.9' of https://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD

KVM/arm64 updates for 6.9

 - Infrastructure for building KVM's trap configuration based on the
   architectural features (or lack thereof) advertised in the VM's ID
   registers

 - Support for mapping vfio-pci BARs as Normal-NC (vaguely similar to
   x86's WC) at stage-2, improving the performance of interacting with
   assigned devices that can tolerate it

 - Conversion of KVM's representation of LPIs to an xarray, utilized to
   address serialization some of the serialization on the LPI injection
   path

 - Support for _architectural_ VHE-only systems, advertised through the
   absence of FEAT_E2H0 in the CPU's ID register

 - Miscellaneous cleanups, fixes, and spelling corrections to KVM and
   selftests

1 files changed, 18 insertions, 1 deletions

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 1cbc990d42e0..df6f99bdf70d 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1862,8 +1862,25 @@ 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 write-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. The assumption is
+	 * 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. Hence VM_ALLOW_ANY_UNCACHED is set in
+	 * the 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;