linux-kernel - Re: [PATCH v7 5/5] KVM: arm64: Support FFA_MSG_SEND_DIRECT

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Message-ID: <aH-oNE4xTakicyC_@willie-the-truck>
Date: Tue, 22 Jul 2025 16:03:16 +0100
From: Will Deacon <will@...nel.org>
To: Per Larsen <perl@...unant.com>
Cc: perlarsen@...gle.com, Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, ahomescu@...gle.com,
	armellel@...gle.com, arve@...roid.com, ayrton@...gle.com,
	qperret@...gle.com, sebastianene@...gle.com, qwandor@...gle.com
Subject: Re: [PATCH v7 5/5] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ2 in
 host handler

On Mon, Jul 21, 2025 at 03:43:42PM -0700, Per Larsen wrote:
> 
> 
> On 7/18/25 6:53 AM, Will Deacon wrote:
> > On Tue, Jul 01, 2025 at 10:06:38PM +0000, Per Larsen via B4 Relay wrote:
> > > From: Per Larsen <perlarsen@...gle.com>
> > > 
> > > FF-A 1.2 adds the DIRECT_REQ2 messaging interface which is similar to
> > > the existing FFA_MSG_SEND_DIRECT_{REQ,RESP} functions except that it
> > > uses the SMC calling convention v1.2 which allows calls to use x4-x17 as
> > > argument and return registers. Add support for FFA_MSG_SEND_DIRECT_REQ2
> > > in the host ffa handler.
> > > 
> > > Signed-off-by: Per Larsen <perlarsen@...gle.com>
> > > ---
> > >   arch/arm64/kvm/hyp/nvhe/ffa.c | 24 +++++++++++++++++++++++-
> > >   include/linux/arm_ffa.h       |  2 ++
> > >   2 files changed, 25 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > > index 79d834120a3f3d26e17e9170c60012b60c6f5a5e..21225988a9365219ccfd69e8e599d7403b5cdf05 100644
> > > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> > > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > > @@ -679,7 +679,6 @@ static bool ffa_call_supported(u64 func_id)
> > >   	case FFA_NOTIFICATION_GET:
> > >   	case FFA_NOTIFICATION_INFO_GET:
> > >   	/* Optional interfaces added in FF-A 1.2 */
> > > -	case FFA_MSG_SEND_DIRECT_REQ2:		/* Optional per 7.5.1 */
> > 
> > I think that's the only change needed. In fact, maybe just don't add it
> > in the earlier patch?
> > 
> > >   	case FFA_MSG_SEND_DIRECT_RESP2:		/* Optional per 7.5.1 */
> > >   	case FFA_CONSOLE_LOG:			/* Optional per 13.1: not in Table 13.1 */
> > >   	case FFA_PARTITION_INFO_GET_REGS:	/* Optional for virtual instances per 13.1 */
> > > @@ -862,6 +861,22 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res,
> > >   	hyp_spin_unlock(&host_buffers.lock);
> > >   }
> > > +static void do_ffa_direct_msg2(struct arm_smccc_1_2_regs *regs,
> > > +			       struct kvm_cpu_context *ctxt,
> > > +			       u64 vm_handle)
> > > +{
> > > +	DECLARE_REG(u32, endp, ctxt, 1);
> > > +
> > > +	struct arm_smccc_1_2_regs *args = (void *)&ctxt->regs.regs[0];
> > > +
> > > +	if (FIELD_GET(FFA_SRC_ENDPOINT_MASK, endp) != vm_handle) {
> > > +		ffa_to_smccc_error(regs, FFA_RET_INVALID_PARAMETERS);
> > > +		return;
> > > +	}
> > 
> > Why do we care about checking the src id? We don't check that for
> > FFA_MSG_SEND_DIRECT_REQ and I don't think we need to care about it here
> > either.
> FFA_MSG_SEND_DIRECT_REQ is handled by do_ffa_direct_msg [0] (in the android
> common kernels, I'm not aware of efforts to upstream this).
>
> I patterned the check in do_ffa_direct_msg2 off the checking done in
> do_ffa_direct_msg. I pressume your reasoning is that this check can
> never fail since we pass in HOST_FFA_ID in kvm_host_ffa_handler. My
> thinking was that we do need to validate the source ID once we start
> using this function for requests that come from a guest VM. I could
> of course add the check in an android-specific patch, WDYT is best?

As long as upstream only has one ID for the whole of non-secure, I don't
think it makes sense to check it. So either we drop this patch or teach
upstream about different IDs, which is probably a separate series.

What I want to avoid is upstream becoming a frankenkernel comprised of
random parts of Android that don't make sense in isolation.

Will