Re: [PATCH v7 0/3] KVM: arm64: Support FF-A direct messaging interfaces

Hi Per,

On Mon, 31 Aug 2026 at 00:08, Per Larsen via B4 Relay
[off-list ref] wrote:

Block host-initiated FF-A direct responses.
Support FFA_MSG_SEND_DIRECT_REQ unconditionally.
Support FFA_MSG_SEND_DIRECT_REQ2 if hypervisor negotiated version 1.2+.

Framework messages (FF-A control plane) are filtered out. For
FFA_MSG_SEND_DIRECT_REQ, we look at flags in w2. Messages using the REQ2
interface are always partition messages.

The third patch was part of a previous patch set [0] but was dropped
since the use case was unclear. A clear use case has now appeared: use
TPM device with CRB over FF-A when kernel boots with pkvm [1].

tpm_crb_ffa already uses sync_send_receive2() for partitions that
support REQ2, and on a pKVM host that returns -EOPNOTSUPP today: the
FF-A driver sets msg_direct_req2_supp when either FFA_FEATURES(REQ2)
or FFA_FEATURES(RESP2) succeeds, and before patch 3 the hypervisor
answers NOT_SUPPORTED to both. Patch 3 lets the REQ2 query through to
firmware, which is enough for the OR. Worth citing that in the cover
instead of [1]?

Tested by booting Android under QEMU.

Which firmware was that, and what did it negotiate for FFA_VERSION?
The proxy doesn't initialise unless firmware answers that call, so I'd
like to know whether a REQ2 in particular round-tripped.

Best Regards,
Per

[0]: https://lore.kernel.org/all/20250730-virtio-msg-ffa-v9-0-7f1b55c8d149@google.com/ (local)
[1]: https://lore.kernel.org/all/20251027191729.1704744-1-yeoreum.yun@arm.com/ (local)

Signed-off-by: Per Larsen <redacted>
---
Changes in v7:
- New patch 1/3: block FFA_FN64_MSG_SEND_DIRECT_RESP. Only the 32-bit
  variant was denied, so the host could send unvalidated 64-bit direct
  responses to EL3, including a forged sender endpoint ID
- Use hyp_smccc_1_2_smc() so the call is bracketed by hyp_exit/hyp_enter;
  the pass-through path already traced these calls
- Declare endp/flags as u64 and reject a non-zero x1[63:32]: these are
  w1/w2, but the raw 64-bit registers are forwarded to EL3
- Pass the canonicalised func_id to do_ffa_direct_msg() rather than
  re-reading x0, which still carries ARM_SMCCC_CALL_HINTS
- Link to v6: https://lore.kernel.org/r/20260501-host-direct-messages-v6-0-3f4af727ed85@google.com (local)

Changes in v6:
- 1/2: validate that bits 31:16 of w1 is HOST_FFA_ID.
- Link to v5: https://lore.kernel.org/r/20260121-host-direct-messages-v5-0-2c1614c94e80@google.com (local)

Changes in v5:
- 1/2: do_ffa_direct_msg: validate that sender is HOST_FFA_ID.
- Link to v4: https://lore.kernel.org/r/20260109-host-direct-messages-v4-0-95da4221d186@google.com (local)

Changes in v4:
- 1/2: do_ffa_direct_msg: check that flag in w2 is zero; drop unused vm_handle parameter.
- 2/2: ffa_call_supported: simplify logic by reordering cases.
-      do_ffa_direct_msg: switch polarity of check and update comment.
- Link to v3: https://lore.kernel.org/r/20251119-host-direct-messages-v3-0-c74d04944b26@google.com (local)

Changes in v3:
- Filter out framework messages as suggested by Will Deacon. Update cover letter accordingly.
- Update trailers: Reviewed-by: Yeoreum Yun [off-list ref]
- Link to v2: https://lore.kernel.org/r/20251030-host-direct-messages-v2-0-9f27cef36730@google.com (local)

Changes in v2:
- 1/2: Drop support for FFA_ID_GET interface in host handler.
- Link to v1: https://lore.kernel.org/r/20251030-host-direct-messages-v1-0-463e57871c8f@google.com (local)

---
Per Larsen (2):
      KVM: arm64: Block host-initiated FF-A direct responses
      KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ2 in host handler

Sebastian Ene (1):
      KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ in host handler

 arch/arm64/kvm/hyp/nvhe/ffa.c | 44 +++++++++++++++++++++++++++++++++++++++++--
 include/linux/arm_ffa.h       |  2 ++
 2 files changed, 44 insertions(+), 2 deletions(-)
---
base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
change-id: 20251029-host-direct-messages-5201d7f55abd

Best regards,
--
Per Larsen [off-list ref]