[PATCH v2 1/4] arm64: Introduce aarch32_enabled()
Robin Murphy
robin.murphy at arm.com
Tue Oct 24 04:56:12 PDT 2023
On 23/10/2023 3:42 pm, Andrea della Porta wrote:
> Aarch32 bit support on 64bit kernels depends on whether CONFIG_COMPAT
> is selected or not. As it is a compile time option it doesn't
> provide the flexibility to have distributions set their own policy for
> Aarch32 support and give the user the flexibility to override it.
>
> As a first step introduce aarch32_enabled() which abstracts whether 32
> bit compat is turned on or off. Upcoming patches will implement
> the ability to set Aarch32 compat state at boot time.
Other than patch #3, which as previously mentioned should be unnecessary
if the kernel correctly never starts an "unsupported" AArch32 process to
begin with, what does this do that simply overriding ID_AA64PFR0_EL1.EL0
via the existing idreg-override mechanism wouldn't?
Thanks,
Robin.
> Signed-off-by: Andrea della Porta <andrea.porta at suse.com>
> ---
> arch/arm64/include/asm/cpufeature.h | 15 +++++++++++++++
> arch/arm64/kernel/entry-common.c | 2 ++
> 2 files changed, 17 insertions(+)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 396af9b9c857..1180d68daaff 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -657,6 +657,21 @@ static inline bool supports_clearbhb(int scope)
> ID_AA64ISAR2_EL1_CLRBHB_SHIFT);
> }
>
> +#ifdef CONFIG_COMPAT
> +extern bool __aarch32_enabled;
> +
> +static inline bool aarch32_enabled(void)
> +{
> + return __aarch32_enabled;
> +}
> +#else /* !CONFIG_COMPAT */
> +
> +static inline bool aarch32_enabled(void)
> +{
> + return false;
> +}
> +#endif
> +
> const struct cpumask *system_32bit_el0_cpumask(void);
> DECLARE_STATIC_KEY_FALSE(arm64_mismatched_32bit_el0);
>
> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
> index 0fc94207e69a..69ff9b8c0bde 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
> @@ -877,6 +877,8 @@ asmlinkage void noinstr el0t_32_error_handler(struct pt_regs *regs)
> {
> __el0_error_handler_common(regs);
> }
> +
> +bool __aarch32_enabled __ro_after_init = true;
> #else /* CONFIG_COMPAT */
> UNHANDLED(el0t, 32, sync)
> UNHANDLED(el0t, 32, irq)
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