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KVM: Rework KVM_CAP_GUEST_MEMFD_MMAP into KVM_CAP_GUEST_MEMFD_FLAGS

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Rework the not-yet-released KVM_CAP_GUEST_MEMFD_MMAP into a more generic
KVM_CAP_GUEST_MEMFD_FLAGS capability so that adding new flags doesn't
require a new capability, and so that developers aren't tempted to bundle
multiple flags into a single capability.

Note, kvm_vm_ioctl_check_extension_generic() can only return a 32-bit
value, but that limitation can be easily circumvented by adding e.g.
KVM_CAP_GUEST_MEMFD_FLAGS2 in the unlikely event guest_memfd supports more
than 32 flags.

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20251003232606.4070510-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2025-10-03 16:25:54 -07:00
parent 034417c143
commit d2042d8f96
4 changed files with 19 additions and 13 deletions
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10
Documentation/virt/kvm/api.rst
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@@ -6432,9 +6432,13 @@ most one mapping per page, i.e. binding multiple memory regions to a single
guest_memfd range is not allowed (any number of memory regions can be bound to
a single guest_memfd file, but the bound ranges must not overlap).
When the capability KVM_CAP_GUEST_MEMFD_MMAP is supported, the 'flags' field
supports GUEST_MEMFD_FLAG_MMAP. Setting this flag on guest_memfd creation
enables mmap() and faulting of guest_memfd memory to host userspace.
The capability KVM_CAP_GUEST_MEMFD_FLAGS enumerates the `flags` that can be
specified via KVM_CREATE_GUEST_MEMFD. Currently defined flags:
============================ ================================================
GUEST_MEMFD_FLAG_MMAP Enable using mmap() on the guest_memfd file
descriptor.
============================ ================================================
When the KVM MMU performs a PFN lookup to service a guest fault and the backing
guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be