[PATCH v2 3/6] KVM: arm64: Allow guest to set the OSLK bit

[Reiji Watanabe]

On Tue, Nov 2, 2021 at 2:47 AM Oliver Upton <oupton at google.com> wrote:
>
> Allow writes to OSLAR and forward the OSLK bit to OSLSR. Change the
> reset value of the OSLK bit to 1. Allow the value to be migrated by
> making OSLSR_EL1.OSLK writable from userspace.
>
> Signed-off-by: Oliver Upton <oupton at google.com>
> ---
>  arch/arm64/include/asm/sysreg.h |  6 ++++++
>  arch/arm64/kvm/sys_regs.c       | 35 +++++++++++++++++++++++++--------
>  2 files changed, 33 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index b268082d67ed..6ba4dc97b69d 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -127,7 +127,13 @@
>  #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 0326b3df0736..acd8aa2e5a44 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;
>
> +       __vcpu_sys_reg(vcpu, rd->reg) = val;
>         return 0;
>  }
>
> @@ -1176,10 +1199,6 @@ static bool access_raz_id_reg(struct kvm_vcpu *vcpu,
>         return __access_id_reg(vcpu, p, r, true);
>  }
>
> -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);
> -
>  /* Visibility overrides for SVE-specific control registers */
>  static unsigned int sve_visibility(const struct kvm_vcpu *vcpu,
>                                    const struct sys_reg_desc *rd)
> @@ -1456,8 +1475,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>         DBG_BCR_BVR_WCR_WVR_EL1(15),
>
>         { SYS_DESC(SYS_MDRAR_EL1), trap_raz_wi },
> -       { SYS_DESC(SYS_OSLAR_EL1), trap_raz_wi },
> -       { SYS_DESC(SYS_OSLSR_EL1), trap_oslsr_el1, reset_val, OSLSR_EL1, 0x00000008,
> +       { SYS_DESC(SYS_OSLAR_EL1), trap_oslar_el1 },
> +       { SYS_DESC(SYS_OSLSR_EL1), trap_oslsr_el1, reset_val, OSLSR_EL1, 0x0000000A,
>                 .set_user = set_oslsr_el1, },

Reviewed-by: Reiji Watanabe <reijiw at google.com>

I assume the reason why you changed the reset value for the
register is because Arm ARM says "the On a Cold reset,
this field resets to 1".

"4.82 KVM_ARM_VCPU_INIT" in Documentation/virt/kvm/api.rst says:
-------------------------------------------------------------
  - System registers: Reset to their architecturally defined
    values as for a warm reset to EL1 (resp. SVC)
-------------------------------------------------------------

Since Arm ARM doesn't say anything about a warm reset for the field,
I would guess the bit doesn't necessarily need to be set.

Thanks,
Reiji


>         { SYS_DESC(SYS_OSDLR_EL1), trap_raz_wi },
>         { SYS_DESC(SYS_DBGPRCR_EL1), trap_raz_wi },
> @@ -1930,7 +1949,7 @@ static const struct sys_reg_desc cp14_regs[] = {
>
>         DBGBXVR(0),
>         /* DBGOSLAR */
> -       { Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_raz_wi },
> +       { Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_oslar_el1 },
>         DBGBXVR(1),
>         /* DBGOSLSR */
>         { Op1( 0), CRn( 1), CRm( 1), Op2( 4), trap_oslsr_el1, NULL, OSLSR_EL1 },
> --
> 2.33.1.1089.g2158813163f-goog
>