On Tue, 20 Feb 2024 12:59:26 +0530 <ankita@xxxxxxxxxx> wrote: > 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; Acked-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
