[PATCH 1/2] arm64: Move handling of erratum 1418040 into C code
Stephen Boyd
swboyd at chromium.org
Tue Jul 28 16:04:08 EDT 2020
Quoting Marc Zyngier (2020-07-28 02:21:11)
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 35de8ba60e3d..44445d471442 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -169,19 +169,6 @@ alternative_cb_end
> stp x28, x29, [sp, #16 * 14]
>
> .if \el == 0
> - .if \regsize == 32
> - /*
> - * If we're returning from a 32-bit task on a system affected by
> - * 1418040 then re-enable userspace access to the virtual counter.
> - */
Can this comment go above the function in C?
> -#ifdef CONFIG_ARM64_ERRATUM_1418040
> -alternative_if ARM64_WORKAROUND_1418040
> - mrs x0, cntkctl_el1
> - orr x0, x0, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN
> - msr cntkctl_el1, x0
> -alternative_else_nop_endif
> -#endif
> - .endif
> clear_gp_regs
> mrs x21, sp_el0
> ldr_this_cpu tsk, __entry_task, x20
> @@ -337,14 +324,6 @@ alternative_else_nop_endif
> tst x22, #PSR_MODE32_BIT // native task?
> b.eq 3f
>
> -#ifdef CONFIG_ARM64_ERRATUM_1418040
> -alternative_if ARM64_WORKAROUND_1418040
> - mrs x0, cntkctl_el1
> - bic x0, x0, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN
> - msr cntkctl_el1, x0
> -alternative_else_nop_endif
> -#endif
> -
> #ifdef CONFIG_ARM64_ERRATUM_845719
> alternative_if ARM64_WORKAROUND_845719
> #ifdef CONFIG_PID_IN_CONTEXTIDR
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 6089638c7d43..87c33f7c536b 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -515,6 +515,34 @@ static void entry_task_switch(struct task_struct *next)
> __this_cpu_write(__entry_task, next);
> }
>
> +static void erratum_1418040_thread_switch(struct task_struct *prev,
Should it be marked __always_inline so that the cpus_have_const_cap()
check can avoid the branch to this function when there's nothing to do?
> + struct task_struct *next)
> +{
> + bool prev32, next32;
> + u64 val;
> +
> + if (!(IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) &&
> + cpus_have_const_cap(ARM64_WORKAROUND_1418040)))
> + return;
> +
> + prev32 = (!(prev->flags & PF_KTHREAD) &&
> + is_compat_thread(task_thread_info(prev)));
> + next32 = (!(next->flags & PF_KTHREAD) &&
> + is_compat_thread(task_thread_info(next)));
> +
> + if (prev32 == next32)
> + return;
> +
> + val = read_sysreg(cntkctl_el1);
> +
> + if (prev32 & !next32)
> + val |= ARCH_TIMER_USR_VCT_ACCESS_EN;
> + else
> + val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN;
> +
> + write_sysreg(val, cntkctl_el1);
> +}
> +
> /*
> * Thread switching.
> */
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