Subject: Re: [PATCH v4 15/26] kvm: arm64: Add SMC handler in nVHE EL2

From: Marc Zyngier <[email-masked]>
Date: Thu, 03 Dec 2020 13:31:18 +0000

On 2020-12-02 18:41, David Brazdil wrote:
> Add handler of host SMCs in KVM nVHE trap handler. Forward all SMCs to
> EL3 and propagate the result back to EL1. This is done in preparation
> for validating host SMCs in KVM protected mode.
> 
> The implementation assumes that firmware uses SMCCC v1.2 or older. That
> means x0-x17 can be used both for arguments and results, other GPRs are
> preserved.
> 
> Signed-off-by: David Brazdil <[email-masked]>
> ---
>  arch/arm64/kvm/hyp/nvhe/host.S     | 38 ++++++++++++++++++++++++++++++
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 35 ++++++++++++++++++++++++---
>  2 files changed, 70 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/host.S 
> b/arch/arm64/kvm/hyp/nvhe/host.S
> index fe2740b224cf..2b56f0bdf874 100644
> --- a/arch/arm64/kvm/hyp/nvhe/host.S
> +++ b/arch/arm64/kvm/hyp/nvhe/host.S
> @@ -180,3 +180,41 @@ SYM_CODE_START(__kvm_hyp_host_vector)
>  	invalid_host_el1_vect			// FIQ 32-bit EL1
>  	invalid_host_el1_vect			// Error 32-bit EL1
>  SYM_CODE_END(__kvm_hyp_host_vector)
> +
> +/*
> + * Forward SMC with arguments in struct kvm_cpu_context, and
> + * store the result into the same struct. Assumes SMCCC 1.2 or older.
> + *
> + * x0: struct kvm_cpu_context*
> + */
> +SYM_CODE_START(__kvm_hyp_host_forward_smc)
> +	/*
> +	 * Use x18 to keep the pointer to the host context because
> +	 * x18 is callee-saved in SMCCC but not in AAPCS64.
> +	 */
> +	mov	x18, x0
> +
> +	ldp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
> +	ldp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
> +	ldp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
> +	ldp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
> +	ldp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
> +	ldp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
> +	ldp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
> +	ldp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
> +	ldp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
> +
> +	smc	#0
> +
> +	stp	x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
> +	stp	x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
> +	stp	x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
> +	stp	x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
> +	stp	x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
> +	stp	x10, x11, [x18, #CPU_XREG_OFFSET(10)]
> +	stp	x12, x13, [x18, #CPU_XREG_OFFSET(12)]
> +	stp	x14, x15, [x18, #CPU_XREG_OFFSET(14)]
> +	stp	x16, x17, [x18, #CPU_XREG_OFFSET(16)]
> +
> +	ret
> +SYM_CODE_END(__kvm_hyp_host_forward_smc)
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index a4f1cac714d7..f25680ede080 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -18,6 +18,8 @@
> 
>  DEFINE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> 
> +void __kvm_hyp_host_forward_smc(struct kvm_cpu_context *host_ctxt);
> +
>  static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
>  {
>  	DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1);
> @@ -152,12 +154,39 @@ static void handle_host_hcall(struct
> kvm_cpu_context *host_ctxt)
>  	cpu_reg(host_ctxt, 0) = SMCCC_RET_NOT_SUPPORTED;
>  }
> 
> +static void default_host_smc_handler(struct kvm_cpu_context 
> *host_ctxt)
> +{
> +	__kvm_hyp_host_forward_smc(host_ctxt);
> +}
> +
> +static void skip_host_instruction(void)
> +{
> +	write_sysreg_el2(read_sysreg_el2(SYS_ELR) + 4, SYS_ELR);
> +}

Just for the sake of keeping things together, it'd be good to
move this helper to include/hyp/adjust_pc.h. Nothing urgent though.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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