Re: [PATCH v8 05/11] KVM: arm64: Enable writable for ID_AA64DFR0_EL1 and ID_DFR0_EL1

[Marc Zyngier <maz@kernel.org>]

On Mon, 07 Aug 2023 17:22:03 +0100,
Jing Zhang <jingzhangos@google.com> wrote:
> 
> All valid fields in ID_AA64DFR0_EL1 and ID_DFR0_EL1 are writable
> from usrespace with this change.

nit: userspace

> 
> Signed-off-by: Jing Zhang <jingzhangos@google.com>
> ---
>  arch/arm64/kvm/sys_regs.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index afade7186675..5f6c2be12e44 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2006,7 +2006,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	  .set_user = set_id_dfr0_el1,
>  	  .visibility = aa32_id_visibility,
>  	  .reset = read_sanitised_id_dfr0_el1,
> -	  .val = ID_DFR0_EL1_PerfMon_MASK, },
> +	  .val = GENMASK(63, 0), },

For obvious reasons, this cannot be a 64 bit mask...

>  	ID_HIDDEN(ID_AFR0_EL1),
>  	AA32_ID_SANITISED(ID_MMFR0_EL1),
>  	AA32_ID_SANITISED(ID_MMFR1_EL1),
> @@ -2055,7 +2055,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	  .get_user = get_id_reg,
>  	  .set_user = set_id_aa64dfr0_el1,
>  	  .reset = read_sanitised_id_aa64dfr0_el1,
> -	  .val = ID_AA64DFR0_EL1_PMUVer_MASK, },
> +	  .val = GENMASK(63, 0), },

What is the actual justification to go from "only the PMU version is
writable" to "everything is writable"?

Also, what about the RES0 fields?

Thanks,

	M.

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