arm64: smp: avoid NMI IPIs with broken MediaTek FW

Some MediaTek devices have broken firmware which corrupts some GICR
registers behind the back of the OS, and pseudo-NMIs cannot be used on
these devices. For more details see commit:

  44bd78dd ("irqchip/gic-v3: Disable pseudo NMIs on Mediatek devices w/ firmware issues")

We did not take this problem into account in commit:

  331a1b3a ("arm64: smp: Add arch support for backtrace using pseudo-NMI")

Since that commit arm64's SMP code will try to setup some IPIs as
pseudo-NMIs, even on systems with broken FW. The GICv3 code will
(rightly) reject attempts to request interrupts as pseudo-NMIs,
resulting in boot-time failures.

Avoid the problem by taking the broken FW into account when deciding to
request IPIs as pseudo-NMIs. The GICv3 driver maintains a static_key
named "supports_pseudo_nmis" which is false on systems with broken FW,
and we can consult this within ipi_should_be_nmi().

Fixes: 331a1b3a ("arm64: smp: Add arch support for backtrace using pseudo-NMI")
Reported-by: Chen-Yu Tsai <wenst@chromium.org>
Closes: https://issuetracker.google.com/issues/197061987#comment68Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/smp.c

@@ -964,7 +964,10 @@ static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
 
 static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
 {
-	if (!system_uses_irq_prio_masking())
+	DECLARE_STATIC_KEY_FALSE(supports_pseudo_nmis);
+
+	if (!system_uses_irq_prio_masking() ||
+	    !static_branch_likely(&supports_pseudo_nmis))
 		return false;
 
 	switch (ipi) {

drivers/irqchip/irq-gic-v3.c

@@ -106,7 +106,7 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
  * - Figure 4-7 Secure read of the priority field for a Non-secure Group 1
  *   interrupt.
  */
-static DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
+DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
 
 DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
 EXPORT_SYMBOL(gic_nonsecure_priorities);