On Sun, 11 Feb 2024 23:17:05 +0530 <ankita@xxxxxxxxxx> wrote: > From: Ankit Agrawal <ankita@xxxxxxxxxx> > > The code to map the MMIO in S2 as NormalNC is enabled when conveyed > that the device is WC safe using a new flag VM_ALLOW_ANY_UNCACHED. > > Make vfio-pci set the VM_ALLOW_ANY_UNCACHED flag. > > This could be extended to other devices in the future once that > is deemed safe. > > Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Acked-by: Jason Gunthorpe <jgg@xxxxxxxxxx> > Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Signed-off-by: Ankit Agrawal <ankita@xxxxxxxxxx> > --- > drivers/vfio/pci/vfio_pci_core.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index 1cbc990d42e0..eba2146202f9 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -1862,8 +1862,12 @@ 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. > + * > + * Set an additional flag VM_ALLOW_ANY_UNCACHED to convey kvm that > + * the device is wc safe. > */ That's a pretty superficial comment. Check that this is accurate, but maybe something like: The VM_ALLOW_ANY_UNCACHED flag is implemented for ARM64, allowing stage 2 device mapping attributes to use Normal-NC rather than DEVICE_nGnRE, which allows guest mappings supporting combining attributes (WC). This attribute has potential risks with the GICv2 VCPU interface, but is expected to be safe for vfio-pci use cases. And specifically, I think these other devices that may be problematic as described in the cover letter is a warning against use for vfio-platform, is that correct? Thanks, Alex > - 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;
