Re: [PATCH 05/13] KVM: arm64: nv: Add trap forwarding for ERET and SMC

[Joey Gouly <joey.gouly@arm.com>]

On Mon, Feb 19, 2024 at 09:20:06AM +0000, Marc Zyngier wrote:
> Honor the trap forwarding bits for both ERET and SMC, using a new
> helper that checks for common conditions.
> 
> Co-developed-by: Jintack Lim <jintack.lim@linaro.org>
> Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---

Reviewed-by: Joey Gouly <joey.gouly@arm.com>

>  arch/arm64/include/asm/kvm_nested.h |  1 +
>  arch/arm64/kvm/emulate-nested.c     | 27 +++++++++++++++++++++++++++
>  arch/arm64/kvm/handle_exit.c        |  7 +++++++
>  3 files changed, 35 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> index c77d795556e1..dbc4e3a67356 100644
> --- a/arch/arm64/include/asm/kvm_nested.h
> +++ b/arch/arm64/include/asm/kvm_nested.h
> @@ -60,6 +60,7 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0)
>  	return ttbr0 & ~GENMASK_ULL(63, 48);
>  }
>  
> +extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
>  
>  int kvm_init_nv_sysregs(struct kvm *kvm);
>  
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index 4697ba41b3a9..2d80e81ae650 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -2117,6 +2117,26 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
>  	return true;
>  }
>  
> +static bool forward_traps(struct kvm_vcpu *vcpu, u64 control_bit)
> +{
> +	bool control_bit_set;
> +
> +	if (!vcpu_has_nv(vcpu))
> +		return false;
> +
> +	control_bit_set = __vcpu_sys_reg(vcpu, HCR_EL2) & control_bit;
> +	if (!is_hyp_ctxt(vcpu) && control_bit_set) {
> +		kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));
> +		return true;
> +	}
> +	return false;
> +}
> +
> +bool forward_smc_trap(struct kvm_vcpu *vcpu)
> +{
> +	return forward_traps(vcpu, HCR_TSC);
> +}
> +
>  static u64 kvm_check_illegal_exception_return(struct kvm_vcpu *vcpu, u64 spsr)
>  {
>  	u64 mode = spsr & PSR_MODE_MASK;
> @@ -2155,6 +2175,13 @@ void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu)
>  	u64 spsr, elr, mode;
>  	bool direct_eret;
>  
> +	/*
> +	 * Forward this trap to the virtual EL2 if the virtual
> +	 * HCR_EL2.NV bit is set and this is coming from !EL2.
> +	 */
> +	if (forward_traps(vcpu, HCR_NV))
> +		return;
> +
>  	/*
>  	 * Going through the whole put/load motions is a waste of time
>  	 * if this is a VHE guest hypervisor returning to its own
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 0646c623d1da..1ccdfe40c691 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -55,6 +55,13 @@ static int handle_hvc(struct kvm_vcpu *vcpu)
>  
>  static int handle_smc(struct kvm_vcpu *vcpu)
>  {
> +	/*
> +	 * Forward this trapped smc instruction to the virtual EL2 if
> +	 * the guest has asked for it.
> +	 */
> +	if (forward_smc_trap(vcpu))
> +		return 1;
> +
>  	/*
>  	 * "If an SMC instruction executed at Non-secure EL1 is
>  	 * trapped to EL2 because HCR_EL2.TSC is 1, the exception is a

Thanks,
Joey