On Tue, 26 Jul 2022 08:37:35 +0100,
Kalesh Singh <kaleshsingh@xxxxxxxxxx> wrote:
>
> Move common on_accessible_stack checks to stacktrace/common.h. This is
> used in the implementation of the nVHE hypervisor unwinder later in
> this series.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
> Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
> Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
> Tested-by: Fuad Tabba <tabba@xxxxxxxxxx>
> ---
>
> Changes in v6:
> - Add Fuad's Tested-by tag
>
> Changes in v5:
> - Add Reviewed-by tags from Mark Brown and Fuad
> - Remove random whitespace change, per Mark Brown
>
> arch/arm64/include/asm/stacktrace.h | 6 ++----
> arch/arm64/include/asm/stacktrace/common.h | 18 ++++++++++++++++++
> 2 files changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index 79f455b37c84..43f4b4a6d383 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -65,8 +65,8 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
> unsigned long sp, unsigned long size,
> struct stack_info *info)
> {
> - if (info)
> - info->type = STACK_TYPE_UNKNOWN;
> + if (on_accessible_stack_common(tsk, sp, size, info))
> + return true;
>
> if (on_task_stack(tsk, sp, size, info))
> return true;
> @@ -74,8 +74,6 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
> return false;
> if (on_irq_stack(sp, size, info))
> return true;
> - if (on_overflow_stack(sp, size, info))
> - return true;
> if (on_sdei_stack(sp, size, info))
> return true;
>
> diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
> index 64ae4f6b06fe..f58b786460d3 100644
> --- a/arch/arm64/include/asm/stacktrace/common.h
> +++ b/arch/arm64/include/asm/stacktrace/common.h
> @@ -62,6 +62,9 @@ struct unwind_state {
> struct task_struct *task;
> };
>
> +static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
> + struct stack_info *info);
> +
> static inline bool on_stack(unsigned long sp, unsigned long size,
> unsigned long low, unsigned long high,
> enum stack_type type, struct stack_info *info)
> @@ -80,6 +83,21 @@ static inline bool on_stack(unsigned long sp, unsigned long size,
> return true;
> }
>
> +static inline bool on_accessible_stack_common(const struct task_struct *tsk,
> + unsigned long sp,
> + unsigned long size,
> + struct stack_info *info)
> +{
> + if (info)
> + info->type = STACK_TYPE_UNKNOWN;
> +
> + /*
> + * Both the kernel and nvhe hypervisor make use of
> + * an overflow_stack
> + */
> + return on_overflow_stack(sp, size, info);
> +}
on_accessible_stack has the following comment:
/*
* We can only safely access per-cpu stacks from current in a non-preemptible
* context.
*/
With this change, I don't think we satisfy this requirement anymore,
as we're checking the overflow stack *before* the preemptible check,
which is a big change in behaviour.
The hypervisor doesn't have this requirement: the unwinding is either
done out of context (nVHE, where EL1 unwinds EL2) or in a
non-preemptible section (pKVM, where the whole thing is
non-preemptible). But the kernel is usually preemptible, so this patch
needs fixing.
I'll see if I can address it locally (I'm currently moving things
around, stay tuned).
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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