[PATCH v3 0/2] KVM: arm64: Support FFA_MEM_RECLAIM2 in host handler

[Snehal Koukuntla]

The Arm Firmware Framework for Arm A-profile (FF-A) v1.3 BET0
specification (DEN0140 rev K) [1] introduces the optional
FFA_MEM_RECLAIM2 (0xC4000091) ABI.

Reclaiming large memory regions with the existing FFA_MEM_RECLAIM ABI
can take significant time, or relies on a stateful time-slicing
mechanism in the Relayer. FFA_MEM_RECLAIM2 allows an Owner to reclaim
exclusive access to a subset of pages from a shared or lent memory
region by passing an array of constituent memory region descriptors in
its TX buffer along with a starting descriptor byte offset and initial
page index. The Relayer returns the number of 4K pages reclaimed in
that invocation without maintaining intermediate transaction state.

On a Pixel board (pKVM, 16K pages, EL3 SPMC), reclaiming a single 16K
range drops from 1.3us to 0.7us (~45% faster) by avoiding
FFA_MEM_RETRIEVE_REQ/RX_RELEASE (~0.6us), and single-call
FFA_MEM_RECLAIM2 stays faster across small range counts (1.3us vs 1.9us
at 16 ranges; 2 calls break even). Up to 64MiB (4096 ranges), batching
256 descriptors/call adds 15 preemption points, capping each EL2/EL3
call at ~11us while keeping total SMC time within 5%.

This series adds the FFA_MEM_RECLAIM2 function ID definition and
implements host proxy support in the pKVM nVHE FF-A handler, unsharing
the reclaimed pages in the host stage-2 page tables upon a successful
reclaim response from EL3/SPMD.

With the FF-A v1.3 specification now at BETA (1.3 BET0), drop the RFC
tag so the series can be considered for merging.

This series is based on v7.4-rc1.

Changes in v3:
- Drop RFC tag now that FF-A v1.3 BET0 (DEN0140 rev K) is released
- Update specification references and links to DEN0140 rev K (1.3 BET0)
- Add benchmark numbers to the cover letter and Patch 2 commit message
- Collect Vincent's Reviewed-by on Patch 2
- Rebase on v7.4-rc1
- Link to v2: https://lore.kernel.org/r/20261016082341.4030770-1-snehalreddy@google.com

Changes in v2:
- Mark as RFC until the FF-A v1.3 specification reaches BETA (Sudeep)
- Rename FFA_FN64_MEM_RECLAIM2 to FFA_MEM_RECLAIM2 (sashiko)
- Check total_pages against the sum of constituent pg_cnt (Vincent)
- Simplify the flags and offset alignment checks (Vincent)
- Rebase on latest kvmarm/next
- Link to v1: https://lore.kernel.org/r/20260921164748.2958578-1-snehalreddy@google.com

[1] https://support.arm.com/documentation/den0140/k

Snehal Koukuntla (2):
  firmware: arm_ffa: Add FFA_MEM_RECLAIM2 function ID
  KVM: arm64: Support FFA_MEM_RECLAIM2 in host handler

 arch/arm64/kvm/hyp/nvhe/ffa.c | 126 ++++++++++++++++++++++++++++++++++
 include/linux/arm_ffa.h       |   1 +
 2 files changed, 127 insertions(+)


base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
-- 
2.56.0.317.g454f8302e1-goog