Re: [PATCH] irqchip/gic-v3: Fix priority comparison when non-secure priorities are used

From: Marc Zyngier
Date: Wed Aug 11 2021 - 14:31:43 EST


+ Alex, who introduced this.

On Wed, 11 Aug 2021 18:15:05 +0100,
Chen-Yu Tsai <wenst@xxxxxxxxxxxx> wrote:
>
> When non-secure priorities are used, compared to the raw priority set,
> the value read back from RPR is also right-shifted by one and the
> highest bit set.
>
> Add a macro to do the modifications to the raw priority when doing the
> comparison against the RPR value. This corrects the pseudo-NMI behavior
> when non-secure priorities in the GIC are used. Tested on 5.10 with
> the "IPI as pseudo-NMI" series [1] applied on MT8195.
>
> [1] https://lore.kernel.org/linux-arm-kernel/1604317487-14543-1-git-send-email-sumit.garg@xxxxxxxxxx/
>
> Fixes: 336780590990 ("irqchip/gic-v3: Support pseudo-NMIs when SCR_EL3.FIQ == 0")
> Signed-off-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx>
> ---
> drivers/irqchip/irq-gic-v3.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index e0f4debe64e1..e7a0b55413db 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -100,6 +100,15 @@ EXPORT_SYMBOL(gic_pmr_sync);
> DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
> EXPORT_SYMBOL(gic_nonsecure_priorities);
>
> +#define GICD_INT_RPR_PRI(priority) \
> + ({ \
> + u32 __priority = (priority); \
> + if (static_branch_unlikely(&gic_nonsecure_priorities)) \
> + __priority = 0x80 | (__priority >> 1); \
> + \
> + __priority; \

This doesn't reflect what the pseudocode says of a read of ICC_RPR_EL1
AFAICS. When the priority is activated, it is indeed shifted. But a
read of RPR does appear to shift things back (and you loose the lowest
bit in the process). Please see 'aarch64/support/ICC_RPR_EL1' in the
architecture spec.

Can you confirm that SCR_EL3.FIQ is set on your system?

Thanks,

M.

> + })
> +
> /* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
> static refcount_t *ppi_nmi_refs;
>
> @@ -687,7 +696,7 @@ static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs
> return;
>
> if (gic_supports_nmi() &&
> - unlikely(gic_read_rpr() == GICD_INT_NMI_PRI)) {
> + unlikely(gic_read_rpr() == GICD_INT_RPR_PRI(GICD_INT_NMI_PRI))) {
> gic_handle_nmi(irqnr, regs);
> return;
> }


--
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