Re: [PATCH v7 2/3] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ in host handler

[Fuad Tabba]

Hi Per, Seb,

On Mon, 31 Aug 2026 at 00:08, Per Larsen via B4 Relay
<devnull+perlarsen.google.com@xxxxxxxxxx> wrote:
[...]
> Allow direct messages to be forwarded from the host. The host should
> not be sending framework messages so they are filtered out.

The patch also rejects a sender ID that isn't HOST_FFA_ID, which the
message doesn't mention. Could you add a line for it?

[...]

> + if (upper_32_bits(endp) ||
> +    FIELD_GET(FFA_SRC_ENDPOINT_MASK, endp) != HOST_FFA_ID) {

Rejecting a non-zero high half of x1 makes sense to me, since EL2
checks bits 31:16 and then forwards the whole register to EL3, and
handle_host_smc() already does the same for x0. x3 to x17 reach EL3 as
the host wrote them though. Was the intent to stop at the registers
this function reads?

[...]

> + struct arm_smccc_1_2_regs *args = (void *)&ctxt->regs.regs[0];

This relies on struct arm_smccc_1_2_regs fitting in the 31 entries of
regs[], which holds today at 18. Could it take a BUILD_BUG_ON, like
do_ffa_mem_xfer() has for its fids?

Cheers,
/fuad