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0c67288e0c
KVM currently forces non-cacheable memory attributes (either Normal-NC or Device-nGnRE) for a region based on pfn_is_map_memory(), i.e. whether or not the kernel has a cacheable alias for it. This is necessary in situations where KVM needs to perform CMOs on the region but is unnecessarily restrictive when hardware obviates the need for CMOs. KVM doesn't need to perform any CMOs on hardware with FEAT_S2FWB and CTR_EL0.DIC. As luck would have it, there are implementations in the wild that need to map regions of a device with cacheable attributes to function properly. An example of this is Nvidia's Grace Hopper/Blackwell systems where GPU memory is interchangeable with DDR and retains properties such as cacheability, unaligned accesses, atomics and handling of executable faults. Of course, for this to work in a VM the GPU memory needs to have a cacheable mapping at stage-2. Allow cacheable stage-2 mappings to be created on supporting hardware when the VMA has cacheable memory attributes. Check these preconditions during memslot creation (in addition to fault handling) to potentially 'fail-fast' as a courtesy to userspace. CC: Oliver Upton <oliver.upton@linux.dev> CC: Sean Christopherson <seanjc@google.com> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> Suggested-by: Catalin Marinas <catalin.marinas@arm.com> Suggested-by: David Hildenbrand <david@redhat.com> Tested-by: Donald Dutile <ddutile@redhat.com> Signed-off-by: Ankit Agrawal <ankita@nvidia.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Link: https://lore.kernel.org/r/20250705071717.5062-6-ankita@nvidia.com [ Oliver: refine changelog, squash kvm_supports_cacheable_pfnmap() patch ] Signed-off-by: Oliver Upton <oliver.upton@linux.dev> |
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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 reStructuredText 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.