Subject: Re: [PATCH v3 3/6] KVM: arm64: Allow guest to set the OSLK bit

From: Marc Zyngier <[email-masked]>
Date: Mon, 29 Nov 2021 11:50:58 +0000

On Tue, 23 Nov 2021 21:01:06 +0000,
Oliver Upton <[email-masked]> wrote:
> 
> Allow writes to OSLAR and forward the OSLK bit to OSLSR. Do nothing with
> the value for now.
> 
> Reviewed-by: Reiji Watanabe <[email-masked]>
> Signed-off-by: Oliver Upton <[email-masked]>
> ---
>  arch/arm64/include/asm/sysreg.h |  6 ++++++
>  arch/arm64/kvm/sys_regs.c       | 33 ++++++++++++++++++++++++++-------
>  2 files changed, 32 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 16b3f1a1d468..9fad61a82047 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -129,7 +129,13 @@
>  #define SYS_DBGWCRn_EL1(n)		sys_reg(2, 0, 0, n, 7)
>  #define SYS_MDRAR_EL1			sys_reg(2, 0, 1, 0, 0)
>  #define SYS_OSLAR_EL1			sys_reg(2, 0, 1, 0, 4)
> +
> +#define SYS_OSLAR_OSLK			BIT(0)
> +
>  #define SYS_OSLSR_EL1			sys_reg(2, 0, 1, 1, 4)
> +
> +#define SYS_OSLSR_OSLK			BIT(1)
> +
>  #define SYS_OSDLR_EL1			sys_reg(2, 0, 1, 3, 4)
>  #define SYS_DBGPRCR_EL1			sys_reg(2, 0, 1, 4, 4)
>  #define SYS_DBGCLAIMSET_EL1		sys_reg(2, 0, 7, 8, 6)
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 7bf350b3d9cd..5dbdb45d6d44 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -44,6 +44,10 @@
>   * 64bit interface.
>   */
>  
> +static int reg_from_user(u64 *val, const void __user *uaddr, u64 id);
> +static int reg_to_user(void __user *uaddr, const u64 *val, u64 id);
> +static u64 sys_reg_to_index(const struct sys_reg_desc *reg);
> +
>  static bool read_from_write_only(struct kvm_vcpu *vcpu,
>  				 struct sys_reg_params *params,
>  				 const struct sys_reg_desc *r)
> @@ -287,6 +291,24 @@ static bool trap_loregion(struct kvm_vcpu *vcpu,
>  	return trap_raz_wi(vcpu, p, r);
>  }
>  
> +static bool trap_oslar_el1(struct kvm_vcpu *vcpu,
> +			   struct sys_reg_params *p,
> +			   const struct sys_reg_desc *r)
> +{
> +	u64 oslsr;
> +
> +	if (!p->is_write)
> +		return read_from_write_only(vcpu, p, r);
> +
> +	/* Forward the OSLK bit to OSLSR */
> +	oslsr = __vcpu_sys_reg(vcpu, OSLSR_EL1) & ~SYS_OSLSR_OSLK;
> +	if (p->regval & SYS_OSLAR_OSLK)
> +		oslsr |= SYS_OSLSR_OSLK;
> +
> +	__vcpu_sys_reg(vcpu, OSLSR_EL1) = oslsr;
> +	return true;
> +}
> +
>  static bool trap_oslsr_el1(struct kvm_vcpu *vcpu,
>  			   struct sys_reg_params *p,
>  			   const struct sys_reg_desc *r)
> @@ -309,9 +331,10 @@ static int set_oslsr_el1(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>  	if (err)
>  		return err;
>  
> -	if (val != rd->val)
> +	if ((val & ~SYS_OSLSR_OSLK) != rd->val)
>  		return -EINVAL;

This looks odd. It means that once I have set the lock from userspace,
I can't clear it?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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