[PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory

[Lorenzo Pieralisi]

On Tue, Dec 05, 2023 at 06:40:42PM +0000, Catalin Marinas wrote:
> On Tue, Dec 05, 2023 at 05:50:27PM +0000, Marc Zyngier wrote:
> > On Tue, 05 Dec 2023 17:33:01 +0000,
> > Catalin Marinas <catalin.marinas at arm.com> wrote:
> > > Ideally we should do this for vfio only but we don't have an easy
> > > way to convey this to KVM.
> > 
> > But if we want to limit this to PCIe, we'll have to find out. The
> > initial proposal (a long while ago) had a flag conveying some
> > information, and I'd definitely feel more confident having something
> > like that.
> 
> We can add a VM_PCI_IO in the high vma flags to be set by
> vfio_pci_core_mmap(), though it limits it to 64-bit architectures. KVM
> knows this is PCI and relaxes things a bit. It's not generic though if
> we need this later for something else.
> 
> A question for Lorenzo: do these BARs appear in iomem_resource? We could
> search that up instead of a flag, something like the page_is_ram()
> helper.

They do but an iomem_resource look-up alone if I am not mistaken would
not tell us if it is PCI address space, we would need additional checks
(like detecting if we are decoding an address within a PCI host bridge
windows) to determine that if we go down this route.

Lorenzo