Re: [PATCH 2/3] KVM: arm64: Bump the supported version of FF-A to 1.2

[Sebastian Ene <sebastianene@google.com>]

On Fri, May 02, 2025 at 02:21:07AM -0700, Per Larsen wrote:
> From: Per Larsen <perlarsen@google.com>
> 
> FF-A version 1.2 introduces the DIRECT_REQ2 ABI. Bump the FF-A version
> preferred by the hypervisor as a precursor to implementing the 1.2-only
> FFA_MSG_SEND_DIRECT_REQ2 and FFA_MSG_SEND_RESP2 messaging interfaces.
> 
> We must also use SMCCC 1.2 for 64-bit SMCs if hypervisor negotiated FF-A
> 1.2, so ffa_set_retval is updated and a new function to call 64-bit smcs
> using SMCCC 1.2 with fallback to SMCCC 1.1 is introduced.
> 
> Update deny-list in ffa_call_supported to mark FFA_NOTIFICATION_* and
> interfaces added in FF-A 1.2 as unsupported lest they get forwarded.
> 
> Co-Developed-by: Ayrton Munoz <ayrton@google.com>
> Signed-off-by: Per Larsen <perlarsen@google.com>
> Signed-off-by: Per Larsen <perl@immunant.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/Makefile |   1 +
>  arch/arm64/kvm/hyp/nvhe/ffa.c    | 109 ++++++++++++++++++++++++++-----
>  2 files changed, 94 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index b43426a493df..95404ff16dac 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -27,6 +27,7 @@ hyp-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o
>  	 cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o stacktrace.o ffa.o
>  hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
>  	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
> +hyp-obj-y += ../../../kernel/smccc-call.o
>  hyp-obj-$(CONFIG_LIST_HARDENED) += list_debug.o
>  hyp-obj-y += $(lib-objs)
>  
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 10e88207b78e..8102dd6a19f7 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -94,13 +94,57 @@ static void ffa_to_smccc_res(struct arm_smccc_res *res, int ret)
>  	ffa_to_smccc_res_prop(res, ret, 0);
>  }
>  
> -static void ffa_set_retval(struct kvm_cpu_context *ctxt,
> +static void ffa_set_retval(u64 func_id,
> +			   struct kvm_cpu_context *ctxt,
>  			   struct arm_smccc_res *res)
>  {
>  	cpu_reg(ctxt, 0) = res->a0;
>  	cpu_reg(ctxt, 1) = res->a1;
>  	cpu_reg(ctxt, 2) = res->a2;
>  	cpu_reg(ctxt, 3) = res->a3;
> +
> +	/*
> +	 * Other result registers must be zero per DEN0077A but SMC32/HVC32 must
> +	 * preserve x8-x30 per DEN0028.
> +	 */
> +	cpu_reg(ctxt, 4) = 0;
> +	cpu_reg(ctxt, 5) = 0;
> +	cpu_reg(ctxt, 6) = 0;
> +	cpu_reg(ctxt, 7) = 0;
> +
> +	/* Per DEN0077A v1.2, x8-x17 must be zero for SMC64/HVC64 results*/
> +	if (ARM_SMCCC_IS_64(func_id) && hyp_ffa_version >= FFA_VERSION_1_2) {

We don't currently handle SMC32 so ARM_SMCCC_IS_64(func_id) should not
be needed and we can also drop the func_id argument.
Also hyp_ffa_version should be accessed with a lock.

> +		cpu_reg(ctxt, 8) = 0;
> +		cpu_reg(ctxt, 9) = 0;
> +		cpu_reg(ctxt, 10) = 0;
> +		cpu_reg(ctxt, 11) = 0;
> +		cpu_reg(ctxt, 12) = 0;
> +		cpu_reg(ctxt, 13) = 0;
> +		cpu_reg(ctxt, 14) = 0;
> +		cpu_reg(ctxt, 15) = 0;
> +		cpu_reg(ctxt, 16) = 0;
> +		cpu_reg(ctxt, 17) = 0;

How can we know from the hypervisor(which is the caller) whether these registers are
used or not by the calee ? IMO this should be TZ responsibility to mitigate the
risk of leaking information through register if these are not used.

> +	}
> +}
> +
> +/* Call SMC64 using SMCCC 1.2 if hyp negotiated FF-A 1.2 falling back to 1.1 */
> +static void arm_smccc_1_2_smc_fallback(u64 func_id, u64 a1, u64 a2, u64 a3,

Should we rename this to arm_smccc_1_x_smc to keep the same name format
?

> +				       u64 a4, u64 a5, u64 a6, u64 a7,
> +				       struct arm_smccc_res *res)
> +{
> +	struct arm_smccc_1_2_regs args, regs;

Initialize regs with {0} to prevent leakaging the hypervisor
stack values in case the callee doesn't make use of it.

> +
> +	/* SMC64 only as SMC32 must preserve x8-x30 per DEN0028 1.6G Sec 2.6 */
> +	if (ARM_SMCCC_IS_64(func_id) && hyp_ffa_version >= FFA_VERSION_1_2) {
> +		args = (struct arm_smccc_1_2_regs) { func_id, a1, a2, a3, a4,
> +						     a5, a6, a7 };
> +		arm_smccc_1_2_smc(&args, &regs);
> +		*res = (struct arm_smccc_res) { .a0 = regs.a0, .a1 = regs.a1,
> +						.a2 = regs.a2, .a3 = regs.a3 };
> +		return;
> +	}
> +
> +	arm_smccc_1_1_smc(func_id, a1, a2, a3, a4, a5, a6, a7, res);
>  }
>  
>  static bool is_ffa_call(u64 func_id)
> @@ -115,12 +159,12 @@ static int ffa_map_hyp_buffers(u64 ffa_page_count)
>  {
>  	struct arm_smccc_res res;
>  
> -	arm_smccc_1_1_smc(FFA_FN64_RXTX_MAP,
> -			  hyp_virt_to_phys(hyp_buffers.tx),
> -			  hyp_virt_to_phys(hyp_buffers.rx),
> -			  ffa_page_count,
> -			  0, 0, 0, 0,
> -			  &res);
> +	arm_smccc_1_2_smc_fallback(FFA_FN64_RXTX_MAP,
> +				   hyp_virt_to_phys(hyp_buffers.tx),
> +				   hyp_virt_to_phys(hyp_buffers.rx),
> +				   ffa_page_count,
> +				   0, 0, 0, 0,
> +				   &res);
>  
>  	return res.a0 == FFA_SUCCESS ? FFA_RET_SUCCESS : res.a2;
>  }
> @@ -174,10 +218,10 @@ static void ffa_mem_reclaim(struct arm_smccc_res *res, u32 handle_lo,
>  
>  static void ffa_retrieve_req(struct arm_smccc_res *res, u32 len)
>  {
> -	arm_smccc_1_1_smc(FFA_FN64_MEM_RETRIEVE_REQ,
> -			  len, len,
> -			  0, 0, 0, 0, 0,
> -			  res);
> +	arm_smccc_1_2_smc_fallback(FFA_FN64_MEM_RETRIEVE_REQ,
> +				   len, len,
> +				   0, 0, 0, 0, 0,
> +				   res);
>  }
>  
>  static void ffa_rx_release(struct arm_smccc_res *res)
> @@ -628,6 +672,37 @@ static bool ffa_call_supported(u64 func_id)
>  	case FFA_RXTX_MAP:
>  	case FFA_MEM_DONATE:
>  	case FFA_MEM_RETRIEVE_REQ:
> +	/* Optional notification interfaces added in FF-A 1.1 */
> +	case FFA_NOTIFICATION_BITMAP_CREATE:
> +	case FFA_NOTIFICATION_BITMAP_DESTROY:
> +	case FFA_NOTIFICATION_BIND:
> +	case FFA_NOTIFICATION_UNBIND:
> +	case FFA_NOTIFICATION_SET:
> +	case FFA_NOTIFICATION_GET:
> +	case FFA_NOTIFICATION_INFO_GET:
> +	/* Unimplemented interfaces added in FF-A 1.2 */
> +	case FFA_MSG_SEND_DIRECT_REQ2:
> +
> +	/*
> +	 * FFA_MSG_SEND_DIRECT_RESP2 is not meant to be invoked by the host or
> +	 * a guest VM because pkvm does not support communication between VMs
> +	 * via FF-A. Direct messages can only be sent from a non-secure sender
> +	 * endpoint to a secure receiver endpoint. Only receiver endpoints are
> +	 * expected to invoke FFA_MSG_SEND_DIRECT_RESP2.
> +	 */
> +	case FFA_MSG_SEND_DIRECT_RESP2:
> +
> +	/* Reserved for secure endpoints per DEN0077A 1.2 REL0 Table 13.53. */

I don't know if the comment is relevant to the upstream code, should we
drop it ? The same with the previous one and few after this.

> +	case FFA_CONSOLE_LOG:
> +
> +	/*
> +	 * Mandatory for secure endpoints per DEN0077A 1.2 REL0 Table 13.1 and
> +	 * optional for non-secure endpoints according to Table 13.38.
> +	 */
> +	case FFA_PARTITION_INFO_GET_REGS:
> +
> +	/* Reserved for secure endpoints per DEN0077A 1.2 REL0 Table 17.2. */
> +	case FFA_EL3_INTR_HANDLE:
>  		return false;
>  	}
>  
> @@ -680,7 +755,8 @@ static int hyp_ffa_post_init(void)
>  	if (res.a0 != FFA_SUCCESS)
>  		return -EOPNOTSUPP;
>  
> -	switch (res.a2) {
> +	/* Bit[0:1] holds minimum buffer size and alignment boundary */
> +	switch (res.a2 & 0x3) {

What is 0x3 ? Can you please define the mask for it ?

>  	case FFA_FEAT_RXTX_MIN_SZ_4K:
>  		min_rxtx_sz = SZ_4K;
>  		break;
> @@ -871,7 +947,7 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
>  
>  	ffa_to_smccc_error(&res, FFA_RET_NOT_SUPPORTED);
>  out_handled:
> -	ffa_set_retval(host_ctxt, &res);
> +	ffa_set_retval(func_id, host_ctxt, &res);
>  	return true;
>  }
>  
> @@ -883,7 +959,7 @@ int hyp_ffa_init(void *pages)
>  	if (kvm_host_psci_config.smccc_version < ARM_SMCCC_VERSION_1_2)
>  		return 0;
>  
> -	arm_smccc_1_1_smc(FFA_VERSION, FFA_VERSION_1_1, 0, 0, 0, 0, 0, 0, &res);
> +	arm_smccc_1_1_smc(FFA_VERSION, FFA_VERSION_1_2, 0, 0, 0, 0, 0, 0, &res);
>  	if (res.a0 == FFA_RET_NOT_SUPPORTED)
>  		return 0;
>  
> @@ -903,10 +979,11 @@ int hyp_ffa_init(void *pages)
>  	if (FFA_MAJOR_VERSION(res.a0) != 1)
>  		return -EOPNOTSUPP;
>  
> -	if (FFA_MINOR_VERSION(res.a0) < FFA_MINOR_VERSION(FFA_VERSION_1_1))
> +	/* See do_ffa_guest_version before bumping maximum supported version. */
> +	if (FFA_MINOR_VERSION(res.a0) < FFA_MINOR_VERSION(FFA_VERSION_1_2))
>  		hyp_ffa_version = res.a0;
>  	else
> -		hyp_ffa_version = FFA_VERSION_1_1;
> +		hyp_ffa_version = FFA_VERSION_1_2;
>  
>  	tx = pages;
>  	pages += KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE;
> -- 
> 2.49.0
>