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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 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 expectation 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. So make vfio-pci set the VM_ALLOW_ANY_UNCACHED flag. Suggested-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Marc Zyngier <maz@kernel.org> Signed-off-by: Ankit Agrawal <ankita@nvidia.com> Link: https://lore.kernel.org/r/20240224150546.368-5-ankita@nvidia.com Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.