On 18.02.2025 15:35, Roger Pau Monne wrote: > When building a PVH dom0 Xen attempts to map all (relevant) MMIO regions > into the p2m for dom0 access. However the information Xen has about the > host memory map is limited. Xen doesn't have access to any resources > described in ACPI dynamic tables, and hence the p2m mappings provided might > not be complete. > > PV doesn't suffer from this issue because a PV dom0 is capable of mapping > into it's page-tables any address not explicitly banned in d->iomem_caps. > > Introduce a new command line options that allows Xen to attempt to fixup > the p2m page-faults, by creating p2m identity maps in response to p2m > page-faults. > > This is aimed as a workaround to small ACPI regions Xen doesn't know about. > Note that missing large MMIO regions mapped in this way will lead to > slowness due to the VM exit processing, plus the mappings will always use > small pages. > > The ultimate aim is to attempt to bring better parity with a classic PV > dom0. > > Note such fixup rely on the CPU doing the access to the unpopulated > address. If the access is attempted from a device instead there's no > possible way to fixup, as IOMMU page-fault are asynchronous. > > Signed-off-by: Roger Pau Monné <roger....@citrix.com>
Reviewed-by: Jan Beulich <jbeul...@suse.com>
