arm64: Make PMR part of task context

In order to replace PSR.I interrupt disabling/enabling with ICC_PMR_EL1
interrupt masking, ICC_PMR_EL1 needs to be saved/restored when
taking/returning from an exception. This mimics the way hardware saves
and restores PSR.I bit in spsr_el1 for exceptions and ERET.

Add PMR to the registers to save in the pt_regs struct upon kernel entry,
and restore it before ERET. Also, initialize it to a sane value when
creating new tasks.
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/processor.h

@@ -191,6 +191,9 @@ static inline void start_thread_common(struct pt_regs *regs, unsigned long pc)
 	memset(regs, 0, sizeof(*regs));
 	forget_syscall(regs);
 	regs->pc = pc;
+
+	if (system_uses_irq_prio_masking())
+		regs->pmr_save = GIC_PRIO_IRQON;
 }
 
 static inline void start_thread(struct pt_regs *regs, unsigned long pc,

arch/arm64/include/asm/ptrace.h

@@ -19,6 +19,8 @@
 #ifndef __ASM_PTRACE_H
 #define __ASM_PTRACE_H
 
+#include <asm/cpufeature.h>
+
 #include <uapi/asm/ptrace.h>
 
 /* Current Exception Level values, as contained in CurrentEL */
@@ -179,7 +181,8 @@ struct pt_regs {
 #endif
 
 	u64 orig_addr_limit;
-	u64 unused;	// maintain 16 byte alignment
+	/* Only valid when ARM64_HAS_IRQ_PRIO_MASKING is enabled. */
+	u64 pmr_save;
 	u64 stackframe[2];
 };
 
@@ -214,8 +217,13 @@ static inline void forget_syscall(struct pt_regs *regs)
 #define processor_mode(regs) \
 	((regs)->pstate & PSR_MODE_MASK)
 
+#define irqs_priority_unmasked(regs)					\
+	(system_uses_irq_prio_masking() ?				\
+		(regs)->pmr_save == GIC_PRIO_IRQON :			\
+		true)
+
 #define interrupts_enabled(regs)			\
-	(!((regs)->pstate & PSR_I_BIT))
+	(!((regs)->pstate & PSR_I_BIT) && irqs_priority_unmasked(regs))
 
 #define fast_interrupts_enabled(regs) \
 	(!((regs)->pstate & PSR_F_BIT))

arch/arm64/kernel/asm-offsets.c

@@ -73,6 +73,7 @@ int main(void)
   DEFINE(S_PC,			offsetof(struct pt_regs, pc));
   DEFINE(S_SYSCALLNO,		offsetof(struct pt_regs, syscallno));
   DEFINE(S_ORIG_ADDR_LIMIT,	offsetof(struct pt_regs, orig_addr_limit));
+  DEFINE(S_PMR_SAVE,		offsetof(struct pt_regs, pmr_save));
   DEFINE(S_STACKFRAME,		offsetof(struct pt_regs, stackframe));
   DEFINE(S_FRAME_SIZE,		sizeof(struct pt_regs));
   BLANK();

arch/arm64/kernel/entry.S

@@ -249,6 +249,12 @@ alternative_else_nop_endif
 	msr	sp_el0, tsk
 	.endif
 
+	/* Save pmr */
+alternative_if ARM64_HAS_IRQ_PRIO_MASKING
+	mrs_s	x20, SYS_ICC_PMR_EL1
+	str	x20, [sp, #S_PMR_SAVE]
+alternative_else_nop_endif
+
 	/*
 	 * Registers that may be useful after this macro is invoked:
 	 *
@@ -269,6 +275,14 @@ alternative_else_nop_endif
 	/* No need to restore UAO, it will be restored from SPSR_EL1 */
 	.endif
 
+	/* Restore pmr */
+alternative_if ARM64_HAS_IRQ_PRIO_MASKING
+	ldr	x20, [sp, #S_PMR_SAVE]
+	msr_s	SYS_ICC_PMR_EL1, x20
+	/* Ensure priority change is seen by redistributor */
+	dsb	sy
+alternative_else_nop_endif
+
 	ldp	x21, x22, [sp, #S_PC]		// load ELR, SPSR
 	.if	\el == 0
 	ct_user_enter

arch/arm64/kernel/process.c

@@ -232,6 +232,9 @@ void __show_regs(struct pt_regs *regs)
 
 	printk("sp : %016llx\n", sp);
 
+	if (system_uses_irq_prio_masking())
+		printk("pmr_save: %08llx\n", regs->pmr_save);
+
 	i = top_reg;
 
 	while (i >= 0) {
@@ -363,6 +366,9 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
 		if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE)
 			childregs->pstate |= PSR_SSBS_BIT;
 
+		if (system_uses_irq_prio_masking())
+			childregs->pmr_save = GIC_PRIO_IRQON;
+
 		p->thread.cpu_context.x19 = stack_start;
 		p->thread.cpu_context.x20 = stk_sz;
 	}