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Subject[PATCH v6 10/24] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking
Date
Instead disabling interrupts by setting the PSR.I bit, use a priority
higher than the one used for interrupts to mask them via PMR.

The value chosen for PMR to enable/disable interrupts encodes the status
of interrupts on a single bit. This information is stored in the irqflags
values used when saving/restoring IRQ status.

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 | 3 +-
arch/arm64/include/asm/irqflags.h | 132 +++++++++++++++++++++++++++++---------
2 files changed, 105 insertions(+), 30 deletions(-)

diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index 7ed3208..3e06891 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -42,7 +42,8 @@

efi_status_t __efi_rt_asm_wrapper(void *, const char *, ...);

-#define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
+#define ARCH_EFI_IRQ_FLAGS_MASK \
+ (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT | ARCH_FLAG_PMR_EN)

/* 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..e0a32e4 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -18,7 +18,27 @@

#ifdef __KERNEL__

+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
#include <asm/ptrace.h>
+#include <asm/sysreg.h>
+
+
+/*
+ * When ICC_PMR_EL1 is used for interrupt masking, only the bit indicating
+ * whether the normal interrupts are masked is kept along with the daif
+ * flags.
+ */
+#define ARCH_FLAG_PMR_EN 0x1
+
+#define MAKE_ARCH_FLAGS(daif, pmr) \
+ ((daif) | (((pmr) >> GIC_PRIO_STATUS_SHIFT) & ARCH_FLAG_PMR_EN))
+
+#define ARCH_FLAGS_GET_PMR(flags) \
+ ((((flags) & ARCH_FLAG_PMR_EN) << GIC_PRIO_STATUS_SHIFT) \
+ | GIC_PRIO_IRQOFF)
+
+#define ARCH_FLAGS_GET_DAIF(flags) ((flags) & ~ARCH_FLAG_PMR_EN)

/*
* Aarch64 has flags for masking: Debug, Asynchronous (serror), Interrupts and
@@ -34,35 +54,62 @@
*/

/*
- * CPU interrupt mask handling.
+ * Local definitions to help us manage between PMR and daif
*/
-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;
-}
+#define _save_daif(dest) \
+ asm volatile("mrs %0, daif" : "=&r" (dest) : : "memory")
+
+#define _restore_daif(daif) \
+ asm volatile("msr daif, %0" : : "r" (daif) : "memory")

+#define _save_pmr(dest) \
+ asm volatile(ALTERNATIVE( \
+ "mov %0, #" __stringify(GIC_PRIO_IRQON), \
+ "mrs_s %0, " __stringify(SYS_ICC_PMR_EL1), \
+ ARM64_HAS_IRQ_PRIO_MASKING) \
+ : "=&r" (dest) \
+ : \
+ : "memory")
+
+#define _restore_pmr(pmr) \
+ asm volatile(ALTERNATIVE( \
+ "nop\n" \
+ "nop", \
+ "msr_s " __stringify(SYS_ICC_PMR_EL1) ",%0\n" \
+ "dsb sy", \
+ ARM64_HAS_IRQ_PRIO_MASKING) \
+ : \
+ : "r" (pmr) \
+ : "memory")
+
+/*
+ * CPU interrupt mask handling.
+ */
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");
}

@@ -71,12 +118,24 @@ static inline void arch_local_irq_disable(void)
*/
static inline unsigned long arch_local_save_flags(void)
{
+ unsigned long daif_flags;
+ unsigned long pmr;
+
+ _save_daif(daif_flags);
+
+ _save_pmr(pmr);
+
+ return MAKE_ARCH_FLAGS(daif_flags, pmr);
+}
+
+static inline unsigned long arch_local_irq_save(void)
+{
unsigned long flags;
- asm volatile(
- "mrs %0, daif // arch_local_save_flags"
- : "=r" (flags)
- :
- : "memory");
+
+ flags = arch_local_save_flags();
+
+ arch_local_irq_disable();
+
return flags;
}

@@ -85,16 +144,31 @@ 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");
+ unsigned long pmr = ARCH_FLAGS_GET_PMR(flags);
+
+ flags = ARCH_FLAGS_GET_DAIF(flags);
+
+ /*
+ * Code switching from PSR.I interrupt disabling to PMR masking
+ * should not lie between consecutive calls to local_irq_save()
+ * and local_irq_restore() in the same context.
+ * So restoring PMR and then the daif flags should be safe.
+ */
+ _restore_pmr(pmr);
+
+ _restore_daif(flags);
}

static inline int arch_irqs_disabled_flags(unsigned long flags)
{
- return flags & PSR_I_BIT;
+ return (ARCH_FLAGS_GET_DAIF(flags) & (PSR_I_BIT)) |
+ !(ARCH_FLAGS_GET_PMR(flags) & GIC_PRIO_STATUS_BIT);
}
+
+#undef _save_daif
+#undef _restore_daif
+#undef _save_pmr
+#undef _restore_pmr
+
#endif
#endif
--
1.9.1
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