[PATCH v8 12/26] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking

[Julien Thierry <julien.thierry@arm.com>]

Instead disabling interrupts by setting the PSR.I bit, use a priority
higher than the one used for interrupts to mask them via PMR.

When using PMR to disable interrupts, the value of PMR will be used
instead of PSR.[DAIF] for the irqflags.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Suggested-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Oleg Nesterov <oleg@redhat.com>
---
 arch/arm64/include/asm/efi.h      |  11 ++++
 arch/arm64/include/asm/irqflags.h | 123 +++++++++++++++++++++++++++++---------
 2 files changed, 106 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index 7ed3208..134ff6e 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -44,6 +44,17 @@
 
 #define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
 
+#define arch_efi_save_flags(state_flags)		\
+	do {						\
+		(state_flags) =	read_sysreg(daif);	\
+	} while (0)
+
+#define arch_efi_restore_flags(state_flags)		\
+	do {						\
+		write_sysreg(state_flags, daif);	\
+	} while (0)
+
+
 /* arch specific definitions used by the stub code */
 
 /*
diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
index 24692ed..fa3b06f 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -18,7 +18,9 @@
 
 #ifdef __KERNEL__
 
+#include <asm/alternative.h>
 #include <asm/ptrace.h>
+#include <asm/sysreg.h>
 
 /*
  * Aarch64 has flags for masking: Debug, Asynchronous (serror), Interrupts and
@@ -36,47 +38,96 @@
 /*
  * CPU interrupt mask handling.
  */
-static inline unsigned long arch_local_irq_save(void)
-{
-	unsigned long flags;
-	asm volatile(
-		"mrs	%0, daif		// arch_local_irq_save\n"
-		"msr	daifset, #2"
-		: "=r" (flags)
-		:
-		: "memory");
-	return flags;
-}
-
 static inline void arch_local_irq_enable(void)
 {
-	asm volatile(
-		"msr	daifclr, #2		// arch_local_irq_enable"
-		:
+	unsigned long unmasked = GIC_PRIO_IRQON;
+
+	asm volatile(ALTERNATIVE(
+		"msr	daifclr, #2		// arch_local_irq_enable\n"
+		"nop",
+		"msr_s  " __stringify(SYS_ICC_PMR_EL1) ",%0\n"
+		"dsb	sy",
+		ARM64_HAS_IRQ_PRIO_MASKING)
 		:
+		: "r" (unmasked)
 		: "memory");
 }
 
 static inline void arch_local_irq_disable(void)
 {
-	asm volatile(
-		"msr	daifset, #2		// arch_local_irq_disable"
-		:
+	unsigned long masked = GIC_PRIO_IRQOFF;
+
+	asm volatile(ALTERNATIVE(
+		"msr	daifset, #2		// arch_local_irq_disable",
+		"msr_s  " __stringify(SYS_ICC_PMR_EL1) ", %0",
+		ARM64_HAS_IRQ_PRIO_MASKING)
 		:
+		: "r" (masked)
 		: "memory");
 }
 
 /*
+ * Having two ways to control interrupt status is a bit complicated. Some
+ * locations like exception entries will have PSR.I bit set by the architecture
+ * while PMR is unmasked.
+ * We need the irqflags to represent that interrupts are disabled in such cases.
+ *
+ * For this, we lower the value read from PMR when the I bit is set so it is
+ * considered as an irq masking priority. (With PMR, lower value means masking
+ * more interrupts).
+ */
+#define _get_irqflags(daif_bits, pmr)					\
+({									\
+	unsigned long flags;						\
+									\
+	BUILD_BUG_ON(GIC_PRIO_IRQOFF < (GIC_PRIO_IRQON & ~PSR_I_BIT));	\
+	asm volatile(ALTERNATIVE(					\
+		"mov	%0, %1\n"					\
+		"nop\n"							\
+		"nop",							\
+		"and	%0, %1, #" __stringify(PSR_I_BIT) "\n"		\
+		"mvn	%0, %0\n"					\
+		"and	%0, %0, %2",					\
+		ARM64_HAS_IRQ_PRIO_MASKING)				\
+		: "=&r" (flags)						\
+		: "r" (daif_bits), "r" (pmr)				\
+		: "memory");						\
+									\
+	flags;								\
+})
+
+/*
  * Save the current interrupt enable state.
  */
 static inline unsigned long arch_local_save_flags(void)
 {
-	unsigned long flags;
-	asm volatile(
-		"mrs	%0, daif		// arch_local_save_flags"
-		: "=r" (flags)
+	unsigned long daif_bits;
+	unsigned long pmr; // Only used if alternative is on
+
+	daif_bits = read_sysreg(daif);
+
+	// Get PMR
+	asm volatile(ALTERNATIVE(
+			"nop",
+			"mrs_s	%0, " __stringify(SYS_ICC_PMR_EL1),
+			ARM64_HAS_IRQ_PRIO_MASKING)
+		: "=&r" (pmr)
 		:
 		: "memory");
+
+	return _get_irqflags(daif_bits, pmr);
+}
+
+#undef _get_irqflags
+
+static inline unsigned long arch_local_irq_save(void)
+{
+	unsigned long flags;
+
+	flags = arch_local_save_flags();
+
+	arch_local_irq_disable();
+
 	return flags;
 }
 
@@ -85,16 +136,32 @@ static inline unsigned long arch_local_save_flags(void)
  */
 static inline void arch_local_irq_restore(unsigned long flags)
 {
-	asm volatile(
-		"msr	daif, %0		// arch_local_irq_restore"
-	:
-	: "r" (flags)
-	: "memory");
+	asm volatile(ALTERNATIVE(
+			"msr	daif, %0\n"
+			"nop",
+			"msr_s	" __stringify(SYS_ICC_PMR_EL1) ", %0\n"
+			"dsb	sy",
+			ARM64_HAS_IRQ_PRIO_MASKING)
+		: "+r" (flags)
+		:
+		: "memory");
 }
 
 static inline int arch_irqs_disabled_flags(unsigned long flags)
 {
-	return flags & PSR_I_BIT;
+	int res;
+
+	asm volatile(ALTERNATIVE(
+			"and	%w0, %w1, #" __stringify(PSR_I_BIT) "\n"
+			"nop",
+			"cmp	%w1, #" __stringify(GIC_PRIO_IRQOFF) "\n"
+			"cset	%w0, ls",
+			ARM64_HAS_IRQ_PRIO_MASKING)
+		: "=&r" (res)
+		: "r" ((int) flags)
+		: "memory");
+
+	return res;
 }
 #endif
 #endif
-- 
1.9.1