Re: [PATCH] arm64: KVM: Hide PMU from guests when disabled

[Christoffer Dall <cdall@linaro.org>]

On Sat, Nov 25, 2017 at 06:40:31PM +0100, Andrew Jones wrote:
> Since commit 93390c0a1b20 ("arm64: KVM: Hide unsupported AArch64 CPU
> features from guests") we can hide cpu features from guests. Apply
> this to a long standing issue where guests see a PMU available, but
> it's not, because it was not enabled by KVM's userspace.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>

> ---
>  arch/arm64/kvm/sys_regs.c | 35 +++++++++++++++++++++--------------
>  1 file changed, 21 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 1830ebc227d1..503144f13af0 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -881,18 +881,25 @@ static bool access_cntp_cval(struct kvm_vcpu *vcpu,
>  }
>  
>  /* Read a sanitised cpufeature ID register by sys_reg_desc */
> -static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
> +static u64 read_id_reg(struct kvm_vcpu *vcpu,
> +		       struct sys_reg_desc const *r,
> +		       bool raz)
>  {
>  	u32 id = sys_reg((u32)r->Op0, (u32)r->Op1,
>  			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
>  	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
>  
> -	if (id == SYS_ID_AA64PFR0_EL1) {
> +	switch (id) {
> +	case SYS_ID_AA64DFR0_EL1:
> +		if (!kvm_arm_pmu_v3_ready(vcpu))
> +			val &= ~(0xfUL << ID_AA64DFR0_PMUVER_SHIFT);
> +		break;
> +	case SYS_ID_AA64PFR0_EL1:
>  		if (val & (0xfUL << ID_AA64PFR0_SVE_SHIFT))
>  			pr_err_once("kvm [%i]: SVE unsupported for guests, suppressing\n",
>  				    task_pid_nr(current));
> -
>  		val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
> +		break;
>  	}
>  
>  	return val;
> @@ -908,7 +915,7 @@ static bool __access_id_reg(struct kvm_vcpu *vcpu,
>  	if (p->is_write)
>  		return write_to_read_only(vcpu, p, r);
>  
> -	p->regval = read_id_reg(r, raz);
> +	p->regval = read_id_reg(vcpu, r, raz);
>  	return true;
>  }
>  
> @@ -937,17 +944,17 @@ static u64 sys_reg_to_index(const struct sys_reg_desc *reg);
>   * are stored, and for set_id_reg() we don't allow the effective value
>   * to be changed.
>   */
> -static int __get_id_reg(const struct sys_reg_desc *rd, void __user *uaddr,
> -			bool raz)
> +static int __get_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> +			void __user *uaddr, bool raz)
>  {
>  	const u64 id = sys_reg_to_index(rd);
> -	const u64 val = read_id_reg(rd, raz);
> +	const u64 val = read_id_reg(vcpu, rd, raz);
>  
>  	return reg_to_user(uaddr, &val, id);
>  }
>  
> -static int __set_id_reg(const struct sys_reg_desc *rd, void __user *uaddr,
> -			bool raz)
> +static int __set_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> +			void __user *uaddr, bool raz)
>  {
>  	const u64 id = sys_reg_to_index(rd);
>  	int err;
> @@ -958,7 +965,7 @@ static int __set_id_reg(const struct sys_reg_desc *rd, void __user *uaddr,
>  		return err;
>  
>  	/* This is what we mean by invariant: you can't change it. */
> -	if (val != read_id_reg(rd, raz))
> +	if (val != read_id_reg(vcpu, rd, raz))
>  		return -EINVAL;
>  
>  	return 0;
> @@ -967,25 +974,25 @@ static int __set_id_reg(const struct sys_reg_desc *rd, void __user *uaddr,
>  static int get_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>  		      const struct kvm_one_reg *reg, void __user *uaddr)
>  {
> -	return __get_id_reg(rd, uaddr, false);
> +	return __get_id_reg(vcpu, rd, uaddr, false);
>  }
>  
>  static int set_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>  		      const struct kvm_one_reg *reg, void __user *uaddr)
>  {
> -	return __set_id_reg(rd, uaddr, false);
> +	return __set_id_reg(vcpu, rd, uaddr, false);
>  }
>  
>  static int get_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>  			  const struct kvm_one_reg *reg, void __user *uaddr)
>  {
> -	return __get_id_reg(rd, uaddr, true);
> +	return __get_id_reg(vcpu, rd, uaddr, true);
>  }
>  
>  static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>  			  const struct kvm_one_reg *reg, void __user *uaddr)
>  {
> -	return __set_id_reg(rd, uaddr, true);
> +	return __set_id_reg(vcpu, rd, uaddr, true);
>  }
>  
>  /* sys_reg_desc initialiser for known cpufeature ID registers */
> -- 
> 2.13.6
>