Hi,
On 2024-01-26 4:38 PM, Nam Cao wrote:
> RISC-V PLIC cannot EOI disabled interrupts, as explained in the
> description of Interrupt Completion in the PLIC spec:
>
> "The PLIC signals it has completed executing an interrupt handler by
> writing the interrupt ID it received from the claim to the claim/complete
> register. The PLIC does not check whether the completion ID is the same
> as the last claim ID for that target. If the completion ID does not match
> an interrupt source that *is currently enabled* for the target, the
> completion is silently ignored."
>
> Commit 69ea463021be ("irqchip/sifive-plic: Fixup EOI failed when masked")
> ensured that by enabling the interrupt if needed before EOI.
>
> Commit a1706a1c5062 ("irqchip/sifive-plic: Separate the enable and mask
> operations") removed the interrupt enabling code from the previous
> commit, because it assumes that interrupt should be enabled at the point
> of EOI. However, this is incorrect: there is a small window after a hart
> claiming an interrupt and before irq_desc->lock getting acquired,
> interrupt can be disabled during this window. Thus, EOI can be invoked
> while the interrupt is disabled, effectively nullify this EOI.
>
> Make sure that interrupt is really enabled before EOI.
Could you please try the patch I previously sent for this issue[1]? It
should fix the bug without complicating the IRQ hot path.
Thanks,
Samuel
[1]: https://lore.kernel.org/lkml/20230717185841.1294425-1-samuel.holland@xxxxxxxxxx/
> Fixes: a1706a1c5062 ("irqchip/sifive-plic: Separate the enable and mask operations")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Nam Cao <namcao@xxxxxxxxxxxxx>
> ---
> drivers/irqchip/irq-sifive-plic.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
> index 5b7bc4fd9517..0857a516c35b 100644
> --- a/drivers/irqchip/irq-sifive-plic.c
> +++ b/drivers/irqchip/irq-sifive-plic.c
> @@ -148,7 +148,13 @@ static void plic_irq_eoi(struct irq_data *d)
> {
> struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
>
> - writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
> + if (irqd_irq_disabled(d)) {
> + plic_toggle(handler, d->hwirq, 1);
> + writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
> + plic_toggle(handler, d->hwirq, 0);
> + } else {
> + writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
> + }
> }
>
> #ifdef CONFIG_SMP
