Re: [RFC PATCH v3 10/29] KVM: arm64: Make ID_AA64DFR0_EL1 writable

[Eric Auger <eauger@redhat.com>]

Hi Reiji,

On 11/17/21 7:43 AM, Reiji Watanabe wrote:
> This patch adds id_reg_info for ID_AA64DFR0_EL1 to make it writable
> by userspace.
> 
> Return an error if userspace tries to set PMUVER field of the
> register to a value that conflicts with the PMU configuration.
> 
> Since number of context-aware breakpoints must be no more than number
> of supported breakpoints according to Arm ARM, return an error
> if userspace tries to set CTX_CMPS field to such value.
> 
> Signed-off-by: Reiji Watanabe <reijiw@google.com>
> ---
>  arch/arm64/kvm/sys_regs.c | 84 ++++++++++++++++++++++++++++++++++-----
>  1 file changed, 73 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 772e3d3067b2..0faf458b0efb 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -626,6 +626,45 @@ static int validate_id_aa64mmfr0_el1(struct kvm_vcpu *vcpu,
>  	return 0;
>  }
>  
> +static bool id_reg_has_pmu(u64 val, u64 shift, unsigned int min)
I would rename the function as the name currently is misleading. The
function validate the val filed @shift againt @min
> +{
> +	unsigned int pmu = cpuid_feature_extract_unsigned_field(val, shift);
> +
> +	/*
> +	 * Treat IMPLEMENTATION DEFINED functionality as unimplemented for
> +	 * ID_AA64DFR0_EL1.PMUVer/ID_DFR0_EL1.PerfMon.
> +	 */
> +	if (pmu == 0xf)
> +		pmu = 0;
Shouldn't we simply forbid the userspace to set 0xF?
> +
> +	return (pmu >= min);
> +}
> +
> +static int validate_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
> +				    const struct id_reg_info *id_reg, u64 val)
> +{
> +	unsigned int brps, ctx_cmps;
> +	bool vcpu_pmu, dfr0_pmu;
> +
> +	brps = cpuid_feature_extract_unsigned_field(val, ID_AA64DFR0_BRPS_SHIFT);
> +	ctx_cmps = cpuid_feature_extract_unsigned_field(val, ID_AA64DFR0_CTX_CMPS_SHIFT);
> +
> +	/*
> +	 * Number of context-aware breakpoints can be no more than number of
> +	 * supported breakpoints.
> +	 */
> +	if (ctx_cmps > brps)
> +		return -EINVAL;
> +
> +	vcpu_pmu = kvm_vcpu_has_pmu(vcpu);
> +	dfr0_pmu = id_reg_has_pmu(val, ID_AA64DFR0_PMUVER_SHIFT, ID_AA64DFR0_PMUVER_8_0);
> +	/* Check if there is a conflict with a request via KVM_ARM_VCPU_INIT */
> +	if (vcpu_pmu ^ dfr0_pmu)
> +		return -EPERM;
> +
> +	return 0;
> +}
> +
>  static void init_id_aa64pfr0_el1_info(struct id_reg_info *id_reg)
>  {
>  	u64 limit = id_reg->vcpu_limit_val;
> @@ -669,6 +708,23 @@ static void init_id_aa64isar1_el1_info(struct id_reg_info *id_reg)
>  		id_reg->vcpu_limit_val &= ~PTRAUTH_MASK;
>  }
>  
> +static void init_id_aa64dfr0_el1_info(struct id_reg_info *id_reg)
> +{
> +	u64 limit = id_reg->vcpu_limit_val;
> +
> +	/* Limit guests to PMUv3 for ARMv8.4 */
> +	limit = cpuid_feature_cap_perfmon_field(limit, ID_AA64DFR0_PMUVER_SHIFT,
> +						ID_AA64DFR0_PMUVER_8_4);
> +	/* Limit debug to ARMv8.0 */
> +	limit &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER);
> +	limit |= (FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER), 6));
> +
> +	/* Hide SPE from guests */
> +	limit &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMSVER);
> +
> +	id_reg->vcpu_limit_val = limit;
> +}
> +
>  static u64 get_reset_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
>  				     const struct id_reg_info *idr)
>  {
> @@ -698,6 +754,14 @@ static u64 get_reset_id_aa64isar1_el1(struct kvm_vcpu *vcpu,
>  	       idr->vcpu_limit_val : (idr->vcpu_limit_val & ~PTRAUTH_MASK);
>  }
>  
> +static u64 get_reset_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
> +				     const struct id_reg_info *idr)
> +{
> +	return kvm_vcpu_has_pmu(vcpu) ?
> +	       idr->vcpu_limit_val :
> +	       (idr->vcpu_limit_val & ~(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER)));
> +}
> +
>  static struct id_reg_info id_aa64pfr0_el1_info = {
>  	.sys_reg = SYS_ID_AA64PFR0_EL1,
>  	.ftr_check_types = S_FCT(ID_AA64PFR0_ASIMD_SHIFT, FCT_LOWER_SAFE) |
> @@ -742,6 +806,14 @@ static struct id_reg_info id_aa64mmfr0_el1_info = {
>  	.validate = validate_id_aa64mmfr0_el1,
>  };
>  
> +static struct id_reg_info id_aa64dfr0_el1_info = {
> +	.sys_reg = SYS_ID_AA64DFR0_EL1,
> +	.ftr_check_types = S_FCT(ID_AA64DFR0_DOUBLELOCK_SHIFT, FCT_LOWER_SAFE),
> +	.init = init_id_aa64dfr0_el1_info,
> +	.validate = validate_id_aa64dfr0_el1,
> +	.get_reset_val = get_reset_id_aa64dfr0_el1,
> +};
> +
>  /*
>   * An ID register that needs special handling to control the value for the
>   * guest must have its own id_reg_info in id_reg_info_table.
> @@ -753,6 +825,7 @@ static struct id_reg_info id_aa64mmfr0_el1_info = {
>  static struct id_reg_info *id_reg_info_table[KVM_ARM_ID_REG_MAX_NUM] = {
>  	[IDREG_IDX(SYS_ID_AA64PFR0_EL1)] = &id_aa64pfr0_el1_info,
>  	[IDREG_IDX(SYS_ID_AA64PFR1_EL1)] = &id_aa64pfr1_el1_info,
> +	[IDREG_IDX(SYS_ID_AA64DFR0_EL1)] = &id_aa64dfr0_el1_info,
>  	[IDREG_IDX(SYS_ID_AA64ISAR0_EL1)] = &id_aa64isar0_el1_info,
>  	[IDREG_IDX(SYS_ID_AA64ISAR1_EL1)] = &id_aa64isar1_el1_info,
>  	[IDREG_IDX(SYS_ID_AA64MMFR0_EL1)] = &id_aa64mmfr0_el1_info,
> @@ -1604,17 +1677,6 @@ static u64 __read_id_reg(const struct kvm_vcpu *vcpu, u32 id)
>  			val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_GIC), gic_lim);
>  		}
>  		break;
> -	case SYS_ID_AA64DFR0_EL1:
> -		/* Limit debug to ARMv8.0 */
> -		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER);
> -		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER), 6);
> -		/* Limit guests to PMUv3 for ARMv8.4 */
> -		val = cpuid_feature_cap_perfmon_field(val,
> -						      ID_AA64DFR0_PMUVER_SHIFT,
> -						      kvm_vcpu_has_pmu(vcpu) ? ID_AA64DFR0_PMUVER_8_4 : 0);
> -		/* Hide SPE from guests */
> -		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMSVER);
> -		break;
>  	case SYS_ID_DFR0_EL1:
>  		/* Limit guests to PMUv3 for ARMv8.4 */
>  		val = cpuid_feature_cap_perfmon_field(val,
> 
Eric


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