[PATCH 08/11] KVM: arm64: Inject AArch32 exceptions from HYP

[James Morse]

Hi Marc,

On 26/10/2020 13:34, Marc Zyngier wrote:
> Similarily to what has been done for AArch64, move the AArch32 exception
> inhjection to HYP.
> 
> In order to not use the regmap selection code at EL2, simplify the code
> populating the target mode's LR register by harcoding the two possible
> LR registers (LR_abt in X20, LR_und in X22).


> diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
> index cd6e643639e8..8d1d1bcd9e69 100644
> --- a/arch/arm64/kvm/hyp/exception.c
> +++ b/arch/arm64/kvm/hyp/exception.c
> @@ -57,10 +67,25 @@ static void __vcpu_write_spsr(struct kvm_vcpu *vcpu, u64 val)

> +static inline u32 __vcpu_read_cp15(const struct kvm_vcpu *vcpu, int reg)
> +{
> +	return __vcpu_read_sys_reg(vcpu, reg / 2);
> +}

Doesn't this re-implement the issue 3204be4109ad biased?


> @@ -155,23 +180,189 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,

> +static void enter_exception32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
> +{

> +	/*
> +	 * Table D1-27 of DDI 0487F.c shows the GPR mapping between
> +	 * AArch32 and AArch64. We only deal with ABT/UND.

(to check I understand : because these are the only two KVM ever injects?)


> +	 */
> +	switch(mode) {
> +	case PSR_AA32_MODE_ABT:
> +		__vcpu_write_spsr_abt(vcpu, host_spsr_to_spsr32(spsr));
> +		lr = 20;
>  		break;
> +		

(two bonus tabs!)


> +	case PSR_AA32_MODE_UND:
> +		__vcpu_write_spsr_und(vcpu, host_spsr_to_spsr32(spsr));
> +		lr = 22;
>  		break;
>  	}> +
> +	vcpu_set_reg(vcpu, lr, *vcpu_pc(vcpu) + return_offset);


Can we, abuse, the compat_lr_abt definitions to do something like:

|	u32 return_address = *vcpu_pc(vcpu) + return_offset;
[..]
|	switch(mode) {
|	case PSR_AA32_MODE_ABT:>
|		__vcpu_write_spsr_abt(vcpu, host_spsr_to_spsr32(spsr));
|		vcpu_gp_regs(vcpu)->compat_lr_abt = return_address;
|		break;
|	case PSR_AA32_MODE_UND:
|		__vcpu_write_spsr_und(vcpu, host_spsr_to_spsr32(spsr));
|		vcpu_gp_regs(vcpu)->compat_lr_und = return_address;
|		break;

...as someone who has no clue about 32bit, this hides all the worrying magic-14==magic-22!



Thanks,

James

> +}