[PATCH v2 1/2] arm64: Move handling of erratum 1418040 into C code
Will Deacon
will at kernel.org
Fri Jul 31 06:41:21 EDT 2020
On Fri, Jul 31, 2020 at 09:33:57AM +0100, Marc Zyngier wrote:
> Instead of dealing with erratum 1418040 on each entry and exit,
> let's move the handling to __switch_to() instead, which has
> several advantages:
>
> - It can be applied when it matters (switching between 32 and 64
> bit tasks).
> - It is written in C (yay!)
> - It can rely on static keys rather than alternatives
>
> Tested-by: Sai Prakash Ranjan <saiprakash.ranjan at codeaurora.org>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
> arch/arm64/kernel/entry.S | 21 ---------------------
> arch/arm64/kernel/process.c | 35 +++++++++++++++++++++++++++++++++++
> 2 files changed, 35 insertions(+), 21 deletions(-)
[...]
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 6089638c7d43..8bbf066224ab 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -515,6 +515,40 @@ static void entry_task_switch(struct task_struct *next)
> __this_cpu_write(__entry_task, next);
> }
>
> +/*
> + * ARM erratum 1418040 handling, affecting the 32bit view of CNTVCT.
> + * Assuming the virtual counter is enabled at the beginning of times:
> + *
> + * - disable access when switching from a 64bit task to a 32bit task
> + * - enable access when switching from a 32bit task to a 64bit task
> + */
> +static __always_inline
Do we need the __always_inline? None of the other calls from __switch_to()
have it.
> +void erratum_1418040_thread_switch(struct task_struct *prev,
> + 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 = is_compat_thread(task_thread_info(prev));
> + next32 = is_compat_thread(task_thread_info(next));
> +
> + if (prev32 == next32)
> + return;
> +
> + val = read_sysreg(cntkctl_el1);
> +
> + if (prev32 & !next32)
I know they're bools but this is perverse!
Why can't it just be:
if (next32)
val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN;
else
val |= ARCH_TIMER_USR_VCT_ACCESS_EN;
?
Will
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