arm64: Always keep DAIF.[IF] in sync

Apple SoCs (A11 and newer) have some interrupt sources hardwired to the
FIQ line. We implement support for this by simply treating IRQs and FIQs
the same way in the interrupt vectors.

To support these systems, the FIQ mask bit needs to be kept in sync with
the IRQ mask bit, so both kinds of exceptions are masked together. No
other platforms should be delivering FIQ exceptions right now, and we
already unmask FIQ in normal process context, so this should not have an
effect on other systems - if spurious FIQs were arriving, they would
already panic the kernel.

Signed-off-by: Hector Martin <[e-mail]>
Signed-off-by: Mark Rutland <[e-mail]>
Tested-by: Hector Martin <[e-mail]>
Cc: James Morse <[e-mail]>
Cc: Marc Zyngier <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Will Deacon <[e-mail]>
Acked-by: Will Deacon <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Catalin Marinas <[e-mail]>

arch/arm64/include/asm/arch_gicv3.h

···
 
 static inline void gic_arch_enable_irqs(void)
 {
-	asm volatile ("msr daifclr, #2" : : : "memory");
+	asm volatile ("msr daifclr, #3" : : : "memory");
 }
 
 #endif /* __ASSEMBLY__ */

arch/arm64/include/asm/assembler.h

···
 	msr	daif, \flags
 	.endm
 
-	/* IRQ is the lowest priority flag, unconditionally unmask the rest. */
-	.macro enable_da_f
-	msr	daifclr, #(8 | 4 | 1)
+	/* IRQ/FIQ are the lowest priority flags, unconditionally unmask the rest. */
+	.macro enable_da
+	msr	daifclr, #(8 | 4)
 	.endm
 
 /*
···
  */
 	.macro	save_and_disable_irq, flags
 	mrs	\flags, daif
-	msr	daifset, #2
+	msr	daifset, #3
 	.endm
 
 	.macro	restore_irq, flags

arch/arm64/include/asm/daifflags.h

···
 #include <asm/ptrace.h>
 
 #define DAIF_PROCCTX		0
-#define DAIF_PROCCTX_NOIRQ	PSR_I_BIT
-#define DAIF_ERRCTX		(PSR_I_BIT | PSR_A_BIT)
+#define DAIF_PROCCTX_NOIRQ	(PSR_I_BIT | PSR_F_BIT)
+#define DAIF_ERRCTX		(PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
 #define DAIF_MASK		(PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
 
 
···
 	if (system_uses_irq_prio_masking()) {
 		/* If IRQs are masked with PMR, reflect it in the flags */
 		if (read_sysreg_s(SYS_ICC_PMR_EL1) != GIC_PRIO_IRQON)
-			flags |= PSR_I_BIT;
+			flags |= PSR_I_BIT | PSR_F_BIT;
 	}
 
 	return flags;
···
 	bool irq_disabled = flags & PSR_I_BIT;
 
 	WARN_ON(system_has_prio_mask_debugging() &&
-		!(read_sysreg(daif) & PSR_I_BIT));
+		(read_sysreg(daif) & (PSR_I_BIT | PSR_F_BIT)) != (PSR_I_BIT | PSR_F_BIT));
 
 	if (!irq_disabled) {
 		trace_hardirqs_on();
···
 			 * If interrupts are disabled but we can take
 			 * asynchronous errors, we can take NMIs
 			 */
-			flags &= ~PSR_I_BIT;
+			flags &= ~(PSR_I_BIT | PSR_F_BIT);
 			pmr = GIC_PRIO_IRQOFF;
 		} else {
 			pmr = GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET;

arch/arm64/include/asm/irqflags.h

···
 
 /*
  * Aarch64 has flags for masking: Debug, Asynchronous (serror), Interrupts and
- * FIQ exceptions, in the 'daif' register. We mask and unmask them in 'dai'
+ * FIQ exceptions, in the 'daif' register. We mask and unmask them in 'daif'
  * order:
  * Masking debug exceptions causes all other exceptions to be masked too/
- * Masking SError masks irq, but not debug exceptions. Masking irqs has no
- * side effects for other flags. Keeping to this order makes it easier for
- * entry.S to know which exceptions should be unmasked.
- *
- * FIQ is never expected, but we mask it when we disable debug exceptions, and
- * unmask it at all other times.
+ * Masking SError masks IRQ/FIQ, but not debug exceptions. IRQ and FIQ are
+ * always masked and unmasked together, and have no side effects for other
+ * flags. Keeping to this order makes it easier for entry.S to know which
+ * exceptions should be unmasked.
  */
 
 /*
···
 	}
 
 	asm volatile(ALTERNATIVE(
-		"msr	daifclr, #2		// arch_local_irq_enable",
+		"msr	daifclr, #3		// arch_local_irq_enable",
 		__msr_s(SYS_ICC_PMR_EL1, "%0"),
 		ARM64_HAS_IRQ_PRIO_MASKING)
 		:
···
 	}
 
 	asm volatile(ALTERNATIVE(
-		"msr	daifset, #2		// arch_local_irq_disable",
+		"msr	daifset, #3		// arch_local_irq_disable",
 		__msr_s(SYS_ICC_PMR_EL1, "%0"),
 		ARM64_HAS_IRQ_PRIO_MASKING)
 		:

arch/arm64/kernel/entry.S

···
 
 	.macro el1_interrupt_handler, handler:req
 	gic_prio_irq_setup pmr=x20, tmp=x1
-	enable_da_f
+	enable_da
 
 	mov	x0, sp
 	bl	enter_el1_irq_or_nmi
···
 	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
+	 * DA were cleared at start of handling, and IF are cleared by
+	 * the GIC irqchip driver using gic_arch_enable_irqs() for
+	 * normal IRQs. If anything is set, it means we come back from
+	 * an NMI instead of a normal IRQ, so skip preemption
 	 */
 	mrs	x0, daif
 	orr	x24, x24, x0
···
 	.macro el0_interrupt_handler, handler:req
 	gic_prio_irq_setup pmr=x20, tmp=x0
 	user_exit_irqoff
-	enable_da_f
+	enable_da
 
 	tbz	x22, #55, 1f
 	bl	do_el0_irq_bp_hardening
···
 	mov	x0, sp
 	mov	x1, x25
 	bl	do_serror
-	enable_da_f
+	enable_da
 	b	ret_to_user
 SYM_CODE_END(el0_error)
 

arch/arm64/kernel/process.c

···
 	unsigned long daif_bits;
 
 	daif_bits = read_sysreg(daif);
-	write_sysreg(daif_bits | PSR_I_BIT, daif);
+	write_sysreg(daif_bits | PSR_I_BIT | PSR_F_BIT, daif);
 
 	/*
 	 * Unmask PMR before going idle to make sure interrupts can

arch/arm64/kernel/smp.c

···
 	cpuflags = read_sysreg(daif);
 
 	WARN_ON(!(cpuflags & PSR_I_BIT));
+	WARN_ON(!(cpuflags & PSR_F_BIT));
 
 	gic_write_pmr(GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET);
 }