Re: [PATCH 01/19] KVM: arm64: Add get_reg_by_id() as a sys_reg_desc retrieving helper

[Reiji Watanabe <reijiw@xxxxxxxxxx>]

Hi Marc,

On Wed, Jul 6, 2022 at 9:43 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> find_reg_by_id() requires a sys_reg_param as input, which most
> users provide as a on-stack variable, but don't make any use of
> the result.
>
> Provide a helper that doesn't have this requirement and simplify
> the callers (all but one).
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
>  arch/arm64/kvm/sys_regs.c        | 28 +++++++++++++++++-----------
>  arch/arm64/kvm/sys_regs.h        |  4 ++++
>  arch/arm64/kvm/vgic-sys-reg-v3.c |  8 ++------
>  3 files changed, 23 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index c06c0477fab5..1f410283c592 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2650,21 +2650,29 @@ const struct sys_reg_desc *find_reg_by_id(u64 id,
>         return find_reg(params, table, num);
>  }
>
> +const struct sys_reg_desc *get_reg_by_id(u64 id,
> +                                        const struct sys_reg_desc table[],
> +                                        unsigned int num)
> +{
> +       struct sys_reg_params params;
> +
> +       if (!index_to_params(id, &params))
> +               return NULL;
> +
> +       return find_reg(&params, table, num);
> +}

Since all the callers of get_reg_id() specify ARRAY_SIZE(array) for
the 3rd argument, and I think future callers of it are also likely to
do the same, perhaps it might be more convenient if we make get_reg_id()
a wrapper macro like below (and rename "get_reg_by_id()" to
"__get_reg_by_id()") ?

#define get_reg_id(id, table)   __get_reg_id(id, table, ARRAY_SIZE(table))

Thanks,
Reiji


> +
>  /* Decode an index value, and find the sys_reg_desc entry. */
>  static const struct sys_reg_desc *index_to_sys_reg_desc(struct kvm_vcpu *vcpu,
>                                                     u64 id)
>  {
>         const struct sys_reg_desc *r;
> -       struct sys_reg_params params;
>
>         /* We only do sys_reg for now. */
>         if ((id & KVM_REG_ARM_COPROC_MASK) != KVM_REG_ARM64_SYSREG)
>                 return NULL;
>
> -       if (!index_to_params(id, &params))
> -               return NULL;
> -
> -       r = find_reg(&params, sys_reg_descs, ARRAY_SIZE(sys_reg_descs));
> +       r = get_reg_by_id(id, sys_reg_descs, ARRAY_SIZE(sys_reg_descs));
>
>         /* Not saved in the sys_reg array and not otherwise accessible? */
>         if (r && !(r->reg || r->get_user))
> @@ -2723,11 +2731,10 @@ static int reg_to_user(void __user *uaddr, const u64 *val, u64 id)
>
>  static int get_invariant_sys_reg(u64 id, void __user *uaddr)
>  {
> -       struct sys_reg_params params;
>         const struct sys_reg_desc *r;
>
> -       r = find_reg_by_id(id, &params, invariant_sys_regs,
> -                          ARRAY_SIZE(invariant_sys_regs));
> +       r = get_reg_by_id(id, invariant_sys_regs,
> +                         ARRAY_SIZE(invariant_sys_regs));
>         if (!r)
>                 return -ENOENT;
>
> @@ -2736,13 +2743,12 @@ static int get_invariant_sys_reg(u64 id, void __user *uaddr)
>
>  static int set_invariant_sys_reg(u64 id, void __user *uaddr)
>  {
> -       struct sys_reg_params params;
>         const struct sys_reg_desc *r;
>         int err;
>         u64 val = 0; /* Make sure high bits are 0 for 32-bit regs */
>
> -       r = find_reg_by_id(id, &params, invariant_sys_regs,
> -                          ARRAY_SIZE(invariant_sys_regs));
> +       r = get_reg_by_id(id, invariant_sys_regs,
> +                         ARRAY_SIZE(invariant_sys_regs));
>         if (!r)
>                 return -ENOENT;
>
> diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
> index aee8ea054f0d..ce30ed9566ae 100644
> --- a/arch/arm64/kvm/sys_regs.h
> +++ b/arch/arm64/kvm/sys_regs.h
> @@ -195,6 +195,10 @@ const struct sys_reg_desc *find_reg_by_id(u64 id,
>                                           const struct sys_reg_desc table[],
>                                           unsigned int num);
>
> +const struct sys_reg_desc *get_reg_by_id(u64 id,
> +                                        const struct sys_reg_desc table[],
> +                                        unsigned int num);
> +
>  #define AA32(_x)       .aarch32_map = AA32_##_x
>  #define Op0(_x)        .Op0 = _x
>  #define Op1(_x)        .Op1 = _x
> diff --git a/arch/arm64/kvm/vgic-sys-reg-v3.c b/arch/arm64/kvm/vgic-sys-reg-v3.c
> index 07d5271e9f05..644acda33c7c 100644
> --- a/arch/arm64/kvm/vgic-sys-reg-v3.c
> +++ b/arch/arm64/kvm/vgic-sys-reg-v3.c
> @@ -263,14 +263,10 @@ static const struct sys_reg_desc gic_v3_icc_reg_descs[] = {
>  int vgic_v3_has_cpu_sysregs_attr(struct kvm_vcpu *vcpu, bool is_write, u64 id,
>                                 u64 *reg)
>  {
> -       struct sys_reg_params params;
>         u64 sysreg = (id & KVM_DEV_ARM_VGIC_SYSREG_MASK) | KVM_REG_SIZE_U64;
>
> -       params.regval = *reg;
> -       params.is_write = is_write;
> -
> -       if (find_reg_by_id(sysreg, &params, gic_v3_icc_reg_descs,
> -                             ARRAY_SIZE(gic_v3_icc_reg_descs)))
> +       if (get_reg_by_id(sysreg, gic_v3_icc_reg_descs,
> +                         ARRAY_SIZE(gic_v3_icc_reg_descs)))
>                 return 0;
>
>         return -ENXIO;
> --
> 2.34.1
>
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