[RFC PATCH v3 00/13] KVM: guest_memfd: Add a common framework for device memory providers

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

Confidential device assignment needs guest_memfd to manage device MMIO as
well as RAM. Device resources such as PCI BARs supply PFNs directly, and
their protected mappings need architecture-specific map and unmap
operations.

This series adds the common guest_memfd support needed by device memory
providers. It builds on the resource-provider API [1] and the existing
folio and RAM PFN backing support.

The VFIO provider, IOMMUFD integration and Arm CCA implementation are
available together at:

  https://git.gitlab.arm.com/linux-arm/linux-cca.git cca/topics/cca-da-gmem-backend

This series depends on the resource-provider groundwork from:
[1] https://lore.kernel.org/all/20261022-gmem-alternative-providers-v2-0-5dd1dc6c660a@google.com

Notes:
* Codex assisted with implementation, review and series organization.

Changes from v2:
https://lore.kernel.org/all/20261017073149.1303738-1-aneesh.kumar@kernel.org
* Rebase on the v2 alternative-provider series and separate the common
  guest_memfd framework from the VFIO, IOMMUFD and Arm CCA integration.
* Introduce backing operations to separate folio, RAM PFN and device MMIO
  handling while sharing locking, invalidation and attribute updates.
* Replace prepare_conversion()/finish_conversion() with non-failing
  lock()/unlock() callbacks.
* Convert device memory through ordinary file-offset attribute updates.
  Derive GPA from memslot bindings and PA from provider PFNs, removing the
  device request object.
* Allow shared and private device PFN lookup in the common layer. Include
  both mapping types in generic invalidation and leave architecture
  mapping policy to the backend.
* Support device range revocation through the common revoke path without
  reclaiming MMIO PFNs or changing attributes.
* Add shared device mmap through the existing get_pfn() fault path. Keep
  VMA protections and flags in the core
* Require only get_pfn() for device providers; lookup_pfn_range() remains
  required for RAM PFN providers.

Changes from v1:
https://lore.kernel.org/all/20261010072504.536230-1-aneesh.kumar@kernel.org
* Require GUEST_MEMFD_FLAG_MMAP to allow VFIO BAR mmap while a provider is
  attached; disable it by default.
* Use the common guest_memfd_provider_operations for folio and PFN
  providers. Select operations through the resource mapping superblock
  and forward VFIO operations to the device driver.

Cc: Ackerley Tng <ackerleytng@google.com>
Cc: Alex Williamson <alex@shazbot.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Joerg Roedel (AMD)" <joro@8bytes.org>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Alexey Kardashevskiy <aik@amd.com>
Cc: Xu Yilun <yilun.xu@linux.intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Fred Griffoul <griffoul@gmail.com>
Cc: iommu@lists.linux.dev
Cc: kvm@vger.kernel.org
Cc: patches@lists.linux.dev


Aneesh Kumar K.V (Arm) (13):
  KVM: guest_memfd: Let providers prepare memory regions
  KVM: guest_memfd: Dispatch attribute conversion through backing
    operations
  KVM: guest_memfd: Let providers coordinate mapping changes
  KVM: guest_memfd: Dispatch revocation through backing operations
  KVM: guest_memfd: Split population by backing type
  KVM: guest_memfd: Support device-backed PFN providers
  KVM: guest_memfd: Support private/shared conversion of device memory
  KVM: guest_memfd: Track private device ranges after attribute updates
  KVM: guest_memfd: Expose device provider private state
  KVM: guest_memfd: Support range revocation of device mappings
  KVM: guest_memfd: Add shared device mmap through PFN providers
  KVM: guest_memfd: Remove device mappings on final close
  KVM: guest_memfd: Invalidate guest_memfd mappings before removing
    memslot bindings

 Documentation/virt/kvm/api.rst |  21 +-
 include/linux/guest_memfd.h    |  84 +++-
 include/linux/kvm_host.h       |   7 +
 virt/kvm/guest_memfd.c         | 690 ++++++++++++++++++++++++++-------
 4 files changed, 660 insertions(+), 142 deletions(-)

-- 
2.43.0