Re: [PATCH v9 24/26] arm64: Skip preemption when exiting an NMI
From: Marc Zyngier
Date: Mon Jan 28 2019 - 07:34:15 EST
On Mon, 21 Jan 2019 15:33:43 +0000,
Julien Thierry <julien.thierry@xxxxxxx> wrote:
> Handling of an NMI should not set any TIF flags. For NMIs received from
> EL0 the current exit path is safe to use.
> However, an NMI received at EL1 could have interrupted some task context
> that has set the TIF_NEED_RESCHED flag. Preempting a task should not
> happen as a result of an NMI.
> Skip preemption after handling an NMI from EL1.
> Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> arch/arm64/kernel/entry.S | 8 ++++++++
> 1 file changed, 8 insertions(+)
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 35a47f6..a0b0a22 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -624,6 +624,14 @@ el1_irq:
> #ifdef CONFIG_PREEMPT
> ldr x24, [tsk, #TSK_TI_PREEMPT] // get preempt count
> +alternative_if ARM64_HAS_IRQ_PRIO_MASKING
> + /*
> + * DA_F were cleared at start of handling. If anything is set in DAIF,
> + * we come back from an NMI, so skip preemption
> + */
> + mrs x0, daif
> + orr x24, x24, x0
> cbnz x24, 1f // preempt count != 0
> bl el1_preempt
I find this a bit ugly, as what we have in x24 is not the preempt
count anymore. Maybe amend the comment above?
The code being nonetheless correct:
Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Jazz is not dead, it just smell funny.