[PATCH v6 19/64] KVM: arm64: nv: Trap SPSR_EL1, ELR_EL1 and VBAR_EL1 from virtual EL2

[Alexandru Elisei]

Hi Marc,

On Fri, Jan 28, 2022 at 12:18:27PM +0000, Marc Zyngier wrote:
> From: Jintack Lim <jintack.lim at linaro.org>
> 
> For the same reason we trap virtual memory register accesses at virtual
> EL2, we need to trap SPSR_EL1, ELR_EL1 and VBAR_EL1 accesses. ARM v8.3
> introduces the HCR_EL2.NV1 bit to be able to trap on those register
> accesses in EL1. Do not set this bit until the whole nesting support is
> completed.
> 
> Signed-off-by: Jintack Lim <jintack.lim at linaro.org>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 9d3520f1d17a..4f2bcc1e0c25 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1650,6 +1650,30 @@ static bool access_sp_el1(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +static bool access_elr(struct kvm_vcpu *vcpu,
> +		       struct sys_reg_params *p,
> +		       const struct sys_reg_desc *r)
> +{
> +	if (p->is_write)
> +		vcpu_write_sys_reg(vcpu, p->regval, ELR_EL1);
> +	else
> +		p->regval = vcpu_read_sys_reg(vcpu, ELR_EL1);

Going over the patch again, I was a bit confused why access_elr() uses
vcpu_{read,write}_sys_reg(), but access_spsr() uses __vcpu_sys_reg(). In
the end, vcpu_{read,write}_sys_reg() will write to the shadow copy of the
registers, as the guest is executing at virtual non-VHE EL2, so the two are
equivalent.

It's obviously me nitpicking, but the inconsistency is unexpected. How
about using vcpu_{read,write}_sys_reg() for access_spsr() below?

Thanks,
Alex

> +
> +	return true;
> +}
> +
> +static bool access_spsr(struct kvm_vcpu *vcpu,
> +			struct sys_reg_params *p,
> +			const struct sys_reg_desc *r)
> +{
> +	if (p->is_write)
> +		__vcpu_sys_reg(vcpu, SPSR_EL1) = p->regval;
> +	else
> +		p->regval = __vcpu_sys_reg(vcpu, SPSR_EL1);
> +
> +	return true;
> +}
> +
>  static bool access_spsr_el2(struct kvm_vcpu *vcpu,
>  			    struct sys_reg_params *p,
>  			    const struct sys_reg_desc *r)
> @@ -1812,6 +1836,9 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	PTRAUTH_KEY(APDB),
>  	PTRAUTH_KEY(APGA),
>  
> +	{ SYS_DESC(SYS_SPSR_EL1), access_spsr},
> +	{ SYS_DESC(SYS_ELR_EL1), access_elr},
> +
>  	{ SYS_DESC(SYS_AFSR0_EL1), access_vm_reg, reset_unknown, AFSR0_EL1 },
>  	{ SYS_DESC(SYS_AFSR1_EL1), access_vm_reg, reset_unknown, AFSR1_EL1 },
>  	{ SYS_DESC(SYS_ESR_EL1), access_vm_reg, reset_unknown, ESR_EL1 },
> @@ -1859,7 +1886,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	{ SYS_DESC(SYS_LORC_EL1), trap_loregion },
>  	{ SYS_DESC(SYS_LORID_EL1), trap_loregion },
>  
> -	{ SYS_DESC(SYS_VBAR_EL1), NULL, reset_val, VBAR_EL1, 0 },
> +	{ SYS_DESC(SYS_VBAR_EL1), access_rw, reset_val, VBAR_EL1, 0 },
>  	{ SYS_DESC(SYS_DISR_EL1), NULL, reset_val, DISR_EL1, 0 },
>  
>  	{ SYS_DESC(SYS_ICC_IAR0_EL1), write_to_read_only },
> -- 
> 2.30.2
>