Re: [PATCH 4/4] KVM: riscv: selftests: Selectively filter-out AIA registers

[Andrew Jones]

On Mon, Sep 18, 2023 at 11:36:46PM +0530, Anup Patel wrote:
> Currently the AIA ONE_REG registers are reported by get-reg-list
> as new registers for various vcpu_reg_list configs whenever Ssaia
> is available on the host because Ssaia extension can only be
> disabled by Smstateen extension which is not always available.
> 
> To tackle this, we should filter-out AIA ONE_REG registers only
> when Ssaia can't be disabled for a VCPU.
> 
> Fixes: 477069398ed6 ("KVM: riscv: selftests: Add get-reg-list test")
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> ---
>  .../selftests/kvm/riscv/get-reg-list.c        | 23 +++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/riscv/get-reg-list.c b/tools/testing/selftests/kvm/riscv/get-reg-list.c
> index 76c0ad11e423..85907c86b835 100644
> --- a/tools/testing/selftests/kvm/riscv/get-reg-list.c
> +++ b/tools/testing/selftests/kvm/riscv/get-reg-list.c
> @@ -12,6 +12,8 @@
>  
>  #define REG_MASK (KVM_REG_ARCH_MASK | KVM_REG_SIZE_MASK)
>  
> +static bool isa_ext_cant_disable[KVM_RISCV_ISA_EXT_MAX];
> +
>  bool filter_reg(__u64 reg)
>  {
>  	switch (reg & ~REG_MASK) {
> @@ -48,6 +50,15 @@ bool filter_reg(__u64 reg)
>  	case KVM_REG_RISCV_ISA_EXT | KVM_RISCV_ISA_EXT_ZIFENCEI:
>  	case KVM_REG_RISCV_ISA_EXT | KVM_RISCV_ISA_EXT_ZIHPM:
>  		return true;
> +	/* AIA registers are always available when Ssaia can't be disabled */
> +	case KVM_REG_RISCV_CSR | KVM_REG_RISCV_CSR_AIA | KVM_REG_RISCV_CSR_AIA_REG(siselect):
> +	case KVM_REG_RISCV_CSR | KVM_REG_RISCV_CSR_AIA | KVM_REG_RISCV_CSR_AIA_REG(iprio1):
> +	case KVM_REG_RISCV_CSR | KVM_REG_RISCV_CSR_AIA | KVM_REG_RISCV_CSR_AIA_REG(iprio2):
> +	case KVM_REG_RISCV_CSR | KVM_REG_RISCV_CSR_AIA | KVM_REG_RISCV_CSR_AIA_REG(sieh):
> +	case KVM_REG_RISCV_CSR | KVM_REG_RISCV_CSR_AIA | KVM_REG_RISCV_CSR_AIA_REG(siph):
> +	case KVM_REG_RISCV_CSR | KVM_REG_RISCV_CSR_AIA | KVM_REG_RISCV_CSR_AIA_REG(iprio1h):
> +	case KVM_REG_RISCV_CSR | KVM_REG_RISCV_CSR_AIA | KVM_REG_RISCV_CSR_AIA_REG(iprio2h):
> +		return isa_ext_cant_disable[KVM_RISCV_ISA_EXT_SSAIA] ? true : false;

No need for the '? true : false'

>  	default:
>  		break;
>  	}
> @@ -71,14 +82,22 @@ static inline bool vcpu_has_ext(struct kvm_vcpu *vcpu, int ext)
>  
>  void finalize_vcpu(struct kvm_vcpu *vcpu, struct vcpu_reg_list *c)
>  {
> +	int rc;
>  	struct vcpu_reg_sublist *s;
> +	unsigned long isa_ext_state[KVM_RISCV_ISA_EXT_MAX] = { 0 };

nit: I think we prefer reverse xmas tree in kselftests, but whatever.

> +
> +	for (int i = 0; i < KVM_RISCV_ISA_EXT_MAX; i++)
> +		__vcpu_get_reg(vcpu, RISCV_ISA_EXT_REG(i), &isa_ext_state[i]);
>  
>  	/*
>  	 * Disable all extensions which were enabled by default
>  	 * if they were available in the risc-v host.
>  	 */
> -	for (int i = 0; i < KVM_RISCV_ISA_EXT_MAX; i++)
> -		__vcpu_set_reg(vcpu, RISCV_ISA_EXT_REG(i), 0);
> +	for (int i = 0; i < KVM_RISCV_ISA_EXT_MAX; i++) {
> +		rc = __vcpu_set_reg(vcpu, RISCV_ISA_EXT_REG(i), 0);
> +		if (rc && isa_ext_state[i])

How helpful is it to check that isa_ext_state[i] isn't zero? The value of
the register could be zero, right? Shouldn't we instead capture the return
values from __vcpu_get_reg and if the return value is zero for a get,
but nonzero for a set, then we know we have it, but can't disable it.

> +			isa_ext_cant_disable[i] = true;
> +	}
>  
>  	for_each_sublist(c, s) {
>  		if (!s->feature)
> -- 
> 2.34.1
>

Thanks,
drew