[PATCH v3 0/5] arm64: pseudo-nmi: elide code when CONFIG_ARM64_PSEUDO_NMI=n

[PATCH v3 0/5] arm64: pseudo-nmi: elide code when CONFIG_ARM64_PSEUDO_NMI=n

[Mark Rutland]

This series addresses a couple of sub-optimal code generation issues with
arm64's pseudo-nmi support code:

* Even when CONFIG_ARM64_PSEUDO_NMI=n, we generate alternative code
  sequences and alt_instr entries which will never be used. This series
  reworks the irqflags code to use alternative branches (with an
  IS_ENABLED() check), which allows the alternatives to be elided when
  CONFIG_ARM64_PSEUDO_NMI=n.

* When PMHE is eanbled in HW, we must synchronize PMR updates using a
  DSB SY. We take pains to avoid this using a static key to skip the
  barrier when PMHE is not in use, but this results in unnecessarily
  branchy code. This series replaces the static key with an alternative,
  allowing the DSB SY to be relaxed to a NOP.

These changes make a defconfig kernel a little smaller, and does not
adversely affect the size of a CONFIG_ARM64_PSEUDO_NMI=y kernel. The
structural changes will also make it easier for a subsequent series to
rework the irqflag and daifflag management, addressing some
long-standing edge cases and preparing for ARMv8.8-A's FEAT_NMI.

I've tested this series under a QEM KVM VM on a ThunderX2 host, and a
QEMU TCG VM on an x86_64 host. I've tested with and without pseudo-NMI
support enabled, and with pseudo-NMI debug and lockdep enabled, using
perf record in system-wide mode.

Since v1 [1]:
* Rename ARM64_HAS_GIC_PRIO_NO_PMHE to ARM64_HAS_GIC_PRIO_RELAXED_SYNC
* Add explanatory comments for cpucap dependencies
* Add patch making ARM64_HAS_GIC_PRIO_MASKING depend on
  ARM64_HAS_GIC_PRIO_MASKING

Since v2 [2]:
* Fix typo in patch 3's subject to refer to ARM64_HAS_GIC_CPUIF_SYSREGS
* Re-home comment regarding PMHE and EL3
* Correct barriers in patch 5
* Explain barrier changes in patch 5's commit message
* Add Reviewed-by tags from Marc

[1] https://lore.kernel.org/linux-arm-kernel/20230123124042.718743-1-mark.rutland@arm.com/
[2] https://lore.kernel.org/linux-arm-kernel/20230125163826.496739-1-mark.rutland@arm.com/

Thanks,
Mark.

Mark Rutland (5):
  arm64: rename ARM64_HAS_SYSREG_GIC_CPUIF to
    ARM64_HAS_GIC_CPUIF_SYSREGS
  arm64: rename ARM64_HAS_IRQ_PRIO_MASKING to ARM64_HAS_GIC_PRIO_MASKING
  arm64: make ARM64_HAS_GIC_PRIO_MASKING depend on
    ARM64_HAS_GIC_CPUIF_SYSREGS
  arm64: add ARM64_HAS_GIC_PRIO_RELAXED_SYNC cpucap
  arm64: irqflags: use alternative branches for pseudo-NMI logic

 arch/arm/include/asm/arch_gicv3.h   |   5 +
 arch/arm64/include/asm/arch_gicv3.h |   5 +
 arch/arm64/include/asm/barrier.h    |  11 +-
 arch/arm64/include/asm/cpufeature.h |   2 +-
 arch/arm64/include/asm/irqflags.h   | 191 +++++++++++++++++++---------
 arch/arm64/include/asm/ptrace.h     |   2 +-
 arch/arm64/kernel/cpufeature.c      |  55 ++++++--
 arch/arm64/kernel/entry.S           |  25 ++--
 arch/arm64/kernel/image-vars.h      |   2 -
 arch/arm64/tools/cpucaps            |   5 +-
 drivers/irqchip/irq-gic-v3.c        |  19 +--
 drivers/irqchip/irq-gic.c           |   2 +-
 12 files changed, 219 insertions(+), 105 deletions(-)

-- 
2.30.2


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[PATCH v3 1/5] arm64: rename ARM64_HAS_SYSREG_GIC_CPUIF to ARM64_HAS_GIC_CPUIF_SYSREGS

[Mark Rutland]

Subsequent patches will add more GIC-related cpucaps. When we do so, it
would be nice to give them a consistent HAS_GIC_* prefix.

In preparation for doing so, this patch renames the existing
ARM64_HAS_SYSREG_GIC_CPUIF cap to ARM64_HAS_GIC_CPUIF_SYSREGS.

The 'CPUIF_SYSREGS' suffix is chosen so that this will be ordered ahead
of other ARM64_HAS_GIC_* definitions in subsequent patches.

The cpucaps file was hand-modified; all other changes were scripted
with:

  find . -type f -name '*.[chS]' -print0 | \
    xargs -0 sed -i
    's/ARM64_HAS_SYSREG_GIC_CPUIF/ARM64_HAS_GIC_CPUIF_SYSREGS/'

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/cpufeature.c | 2 +-
 arch/arm64/tools/cpucaps       | 2 +-
 drivers/irqchip/irq-gic.c      | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index a77315b338e6..ad2a1f5503f3 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2142,7 +2142,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	},
 	{
 		.desc = "GIC system register CPU interface",
-		.capability = ARM64_HAS_SYSREG_GIC_CPUIF,
+		.capability = ARM64_HAS_GIC_CPUIF_SYSREGS,
 		.type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE,
 		.matches = has_useable_gicv3_cpuif,
 		.sys_reg = SYS_ID_AA64PFR0_EL1,
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index a86ee376920a..373eb148498e 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -28,6 +28,7 @@ HAS_GENERIC_AUTH
 HAS_GENERIC_AUTH_ARCH_QARMA3
 HAS_GENERIC_AUTH_ARCH_QARMA5
 HAS_GENERIC_AUTH_IMP_DEF
+HAS_GIC_CPUIF_SYSREGS
 HAS_IRQ_PRIO_MASKING
 HAS_LDAPR
 HAS_LSE_ATOMICS
@@ -38,7 +39,6 @@ HAS_RAS_EXTN
 HAS_RNG
 HAS_SB
 HAS_STAGE2_FWB
-HAS_SYSREG_GIC_CPUIF
 HAS_TIDCP1
 HAS_TLB_RANGE
 HAS_VIRT_HOST_EXTN
diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index 210bc2f4d555..6ae697a3800d 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -54,7 +54,7 @@
 
 static void gic_check_cpu_features(void)
 {
-	WARN_TAINT_ONCE(this_cpu_has_cap(ARM64_HAS_SYSREG_GIC_CPUIF),
+	WARN_TAINT_ONCE(this_cpu_has_cap(ARM64_HAS_GIC_CPUIF_SYSREGS),
 			TAINT_CPU_OUT_OF_SPEC,
 			"GICv3 system registers enabled, broken firmware!\n");
 }
-- 
2.30.2


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[PATCH v3 2/5] arm64: rename ARM64_HAS_IRQ_PRIO_MASKING to ARM64_HAS_GIC_PRIO_MASKING

[Mark Rutland]

Subsequent patches will add more GIC-related cpucaps. When we do so, it
would be nice to give them a consistent HAS_GIC_* prefix.

In preparation for doing so, this patch renames the existing
ARM64_HAS_IRQ_PRIO_MASKING cap to ARM64_HAS_GIC_PRIO_MASKING.

The cpucaps file was hand-modified; all other changes were scripted
with:

  find . -type f -name '*.[chS]' -print0 | \
    xargs -0 sed -i 's/ARM64_HAS_IRQ_PRIO_MASKING/ARM64_HAS_GIC_PRIO_MASKING/'

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h |  2 +-
 arch/arm64/include/asm/irqflags.h   | 10 +++++-----
 arch/arm64/include/asm/ptrace.h     |  2 +-
 arch/arm64/kernel/cpufeature.c      |  2 +-
 arch/arm64/kernel/entry.S           |  4 ++--
 arch/arm64/tools/cpucaps            |  2 +-
 6 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 03d1c9d7af82..c50928398e4b 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -806,7 +806,7 @@ static inline bool system_has_full_ptr_auth(void)
 static __always_inline bool system_uses_irq_prio_masking(void)
 {
 	return IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) &&
-	       cpus_have_const_cap(ARM64_HAS_IRQ_PRIO_MASKING);
+	       cpus_have_const_cap(ARM64_HAS_GIC_PRIO_MASKING);
 }
 
 static inline bool system_supports_mte(void)
diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
index b57b9b1e4344..f51653fb90e4 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -35,7 +35,7 @@ static inline void arch_local_irq_enable(void)
 	asm volatile(ALTERNATIVE(
 		"msr	daifclr, #3		// arch_local_irq_enable",
 		__msr_s(SYS_ICC_PMR_EL1, "%0"),
-		ARM64_HAS_IRQ_PRIO_MASKING)
+		ARM64_HAS_GIC_PRIO_MASKING)
 		:
 		: "r" ((unsigned long) GIC_PRIO_IRQON)
 		: "memory");
@@ -54,7 +54,7 @@ static inline void arch_local_irq_disable(void)
 	asm volatile(ALTERNATIVE(
 		"msr	daifset, #3		// arch_local_irq_disable",
 		__msr_s(SYS_ICC_PMR_EL1, "%0"),
-		ARM64_HAS_IRQ_PRIO_MASKING)
+		ARM64_HAS_GIC_PRIO_MASKING)
 		:
 		: "r" ((unsigned long) GIC_PRIO_IRQOFF)
 		: "memory");
@@ -70,7 +70,7 @@ static inline unsigned long arch_local_save_flags(void)
 	asm volatile(ALTERNATIVE(
 		"mrs	%0, daif",
 		__mrs_s("%0", SYS_ICC_PMR_EL1),
-		ARM64_HAS_IRQ_PRIO_MASKING)
+		ARM64_HAS_GIC_PRIO_MASKING)
 		: "=&r" (flags)
 		:
 		: "memory");
@@ -85,7 +85,7 @@ static inline int arch_irqs_disabled_flags(unsigned long flags)
 	asm volatile(ALTERNATIVE(
 		"and	%w0, %w1, #" __stringify(PSR_I_BIT),
 		"eor	%w0, %w1, #" __stringify(GIC_PRIO_IRQON),
-		ARM64_HAS_IRQ_PRIO_MASKING)
+		ARM64_HAS_GIC_PRIO_MASKING)
 		: "=&r" (res)
 		: "r" ((int) flags)
 		: "memory");
@@ -122,7 +122,7 @@ static inline void arch_local_irq_restore(unsigned long flags)
 	asm volatile(ALTERNATIVE(
 		"msr	daif, %0",
 		__msr_s(SYS_ICC_PMR_EL1, "%0"),
-		ARM64_HAS_IRQ_PRIO_MASKING)
+		ARM64_HAS_GIC_PRIO_MASKING)
 		:
 		: "r" (flags)
 		: "memory");
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 41b332c054ab..47ec58031f11 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -194,7 +194,7 @@ struct pt_regs {
 	u32 unused2;
 #endif
 	u64 sdei_ttbr1;
-	/* Only valid when ARM64_HAS_IRQ_PRIO_MASKING is enabled. */
+	/* Only valid when ARM64_HAS_GIC_PRIO_MASKING is enabled. */
 	u64 pmr_save;
 	u64 stackframe[2];
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index ad2a1f5503f3..afd547a5309c 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2534,7 +2534,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		 * Depends on having GICv3
 		 */
 		.desc = "IRQ priority masking",
-		.capability = ARM64_HAS_IRQ_PRIO_MASKING,
+		.capability = ARM64_HAS_GIC_PRIO_MASKING,
 		.type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE,
 		.matches = can_use_gic_priorities,
 		.sys_reg = SYS_ID_AA64PFR0_EL1,
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 11cb99c4d298..e2d1d3d5de1d 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -312,7 +312,7 @@ alternative_else_nop_endif
 
 #ifdef CONFIG_ARM64_PSEUDO_NMI
 	/* Save pmr */
-alternative_if ARM64_HAS_IRQ_PRIO_MASKING
+alternative_if ARM64_HAS_GIC_PRIO_MASKING
 	mrs_s	x20, SYS_ICC_PMR_EL1
 	str	x20, [sp, #S_PMR_SAVE]
 	mov	x20, #GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET
@@ -337,7 +337,7 @@ alternative_else_nop_endif
 
 #ifdef CONFIG_ARM64_PSEUDO_NMI
 	/* Restore pmr */
-alternative_if ARM64_HAS_IRQ_PRIO_MASKING
+alternative_if ARM64_HAS_GIC_PRIO_MASKING
 	ldr	x20, [sp, #S_PMR_SAVE]
 	msr_s	SYS_ICC_PMR_EL1, x20
 	mrs_s	x21, SYS_ICC_CTLR_EL1
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 373eb148498e..c993d43624b3 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -29,7 +29,7 @@ HAS_GENERIC_AUTH_ARCH_QARMA3
 HAS_GENERIC_AUTH_ARCH_QARMA5
 HAS_GENERIC_AUTH_IMP_DEF
 HAS_GIC_CPUIF_SYSREGS
-HAS_IRQ_PRIO_MASKING
+HAS_GIC_PRIO_MASKING
 HAS_LDAPR
 HAS_LSE_ATOMICS
 HAS_NO_FPSIMD
-- 
2.30.2


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[PATCH v3 3/5] arm64: make ARM64_HAS_GIC_PRIO_MASKING depend on ARM64_HAS_GIC_CPUIF_SYSREGS

[Mark Rutland]

Currently the arm64_cpu_capabilities structure for
ARM64_HAS_GIC_PRIO_MASKING open-codes the same CPU field definitions as
the arm64_cpu_capabilities structure for ARM64_HAS_GIC_CPUIF_SYSREGS, so
that can_use_gic_priorities() can use has_useable_gicv3_cpuif().

This duplication isn't ideal for the legibility of the code, and sets a
bad example for any ARM64_HAS_GIC_* definitions added by subsequent
patches.

Instead, have ARM64_HAS_GIC_PRIO_MASKING check for the
ARM64_HAS_GIC_CPUIF_SYSREGS cpucap, and add a comment explaining why
this is safe. Subsequent patches will use the same pattern where one
cpucap depends upon another.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/cpufeature.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index afd547a5309c..515975f42d03 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2046,7 +2046,15 @@ early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
 static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
 				   int scope)
 {
-	return enable_pseudo_nmi && has_useable_gicv3_cpuif(entry, scope);
+	/*
+	 * ARM64_HAS_GIC_CPUIF_SYSREGS has a lower index, and is a boot CPU
+	 * feature, so will be detected earlier.
+	 */
+	BUILD_BUG_ON(ARM64_HAS_GIC_PRIO_MASKING <= ARM64_HAS_GIC_CPUIF_SYSREGS);
+	if (!cpus_have_cap(ARM64_HAS_GIC_CPUIF_SYSREGS))
+		return false;
+
+	return enable_pseudo_nmi;
 }
 #endif
 
@@ -2537,11 +2545,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.capability = ARM64_HAS_GIC_PRIO_MASKING,
 		.type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE,
 		.matches = can_use_gic_priorities,
-		.sys_reg = SYS_ID_AA64PFR0_EL1,
-		.field_pos = ID_AA64PFR0_EL1_GIC_SHIFT,
-		.field_width = 4,
-		.sign = FTR_UNSIGNED,
-		.min_field_value = 1,
 	},
 #endif
 #ifdef CONFIG_ARM64_E0PD
-- 
2.30.2


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[PATCH v3 4/5] arm64: add ARM64_HAS_GIC_PRIO_RELAXED_SYNC cpucap

[Mark Rutland]

When Priority Mask Hint Enable (PMHE) == 0b1, the GIC may use the PMR
value to determine whether to signal an IRQ to a PE, and consequently
after a change to the PMR value, a DSB SY may be required to ensure that
interrupts are signalled to a CPU in finite time. When PMHE == 0b0,
interrupts are always signalled to the relevant PE, and all masking
occurs locally, without requiring a DSB SY.

Since commit:

  f226650494c6aa87 ("arm64: Relax ICC_PMR_EL1 accesses when ICC_CTLR_EL1.PMHE is clear")

... we handle this dynamically: in most cases a static key is used to
determine whether to issue a DSB SY, but the entry code must read from
ICC_CTLR_EL1 as static keys aren't accessible from plain assembly.

It would be much nicer to use an alternative instruction sequence for
the DSB, as this would avoid the need to read from ICC_CTLR_EL1 in the
entry code, and for most other code this will result in simpler code
generation with fewer instructions and fewer branches.

This patch adds a new ARM64_HAS_GIC_PRIO_RELAXED_SYNC cpucap which is
only set when ICC_CTLR_EL1.PMHE == 0b0 (and GIC priority masking is in
use). This allows us to replace the existing users of the
`gic_pmr_sync` static key with alternative sequences which default to a
DSB SY and are relaxed to a NOP when PMHE is not in use.

The entry assembly management of the PMR is slightly restructured to use
a branch (rather than multiple NOPs) when priority masking is not in
use. This is more in keeping with other alternatives in the entry
assembly, and permits the use of a separate alternatives for the
PMHE-dependent DSB SY (and removal of the conditional branch this
currently requires). For consistency I've adjusted both the save and
restore paths.

According to bloat-o-meter, when building defconfig +
CONFIG_ARM64_PSEUDO_NMI=y this shrinks the kernel text by ~4KiB:

| add/remove: 4/2 grow/shrink: 42/310 up/down: 332/-5032 (-4700)

The resulting vmlinux is ~66KiB smaller, though the resulting Image size
is unchanged due to padding and alignment:

| [mark@lakrids:~/src/linux]% ls -al vmlinux-*
| -rwxr-xr-x 1 mark mark 137508344 Jan 17 14:11 vmlinux-after
| -rwxr-xr-x 1 mark mark 137575440 Jan 17 13:49 vmlinux-before
| [mark@lakrids:~/src/linux]% ls -al Image-*
| -rw-r--r-- 1 mark mark 38777344 Jan 17 14:11 Image-after
| -rw-r--r-- 1 mark mark 38777344 Jan 17 13:49 Image-before

Prior to this patch we did not verify the state of ICC_CTLR_EL1.PMHE on
secondary CPUs. As of this patch this is verified by the cpufeature code
when using GIC priority masking (i.e. when using pseudo-NMIs).

Note that since commit:

  7e3a57fa6ca831fa ("arm64: Document ICC_CTLR_EL3.PMHE setting requirements")

... Documentation/arm64/booting.rst specifies:

|      - ICC_CTLR_EL3.PMHE (bit 6) must be set to the same value across
|        all CPUs the kernel is executing on, and must stay constant
|        for the lifetime of the kernel.

... so that should not adversely affect any compliant systems, and as
we'll only check for the absense of PMHE when using pseudo-NMIs, this
will only fire when such mismatch will adversely affect the system.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm/include/asm/arch_gicv3.h   |  5 ++++
 arch/arm64/include/asm/arch_gicv3.h |  5 ++++
 arch/arm64/include/asm/barrier.h    | 11 +++++----
 arch/arm64/kernel/cpufeature.c      | 36 +++++++++++++++++++++++++++++
 arch/arm64/kernel/entry.S           | 25 ++++++++++++--------
 arch/arm64/kernel/image-vars.h      |  2 --
 arch/arm64/tools/cpucaps            |  1 +
 drivers/irqchip/irq-gic-v3.c        | 19 +--------------
 8 files changed, 71 insertions(+), 33 deletions(-)

diff --git a/arch/arm/include/asm/arch_gicv3.h b/arch/arm/include/asm/arch_gicv3.h
index f82a819eb0db..311e83038bdb 100644
--- a/arch/arm/include/asm/arch_gicv3.h
+++ b/arch/arm/include/asm/arch_gicv3.h
@@ -252,5 +252,10 @@ static inline void gic_arch_enable_irqs(void)
 	WARN_ON_ONCE(true);
 }
 
+static inline bool gic_has_relaxed_pmr_sync(void)
+{
+	return false;
+}
+
 #endif /* !__ASSEMBLY__ */
 #endif /* !__ASM_ARCH_GICV3_H */
diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
index 48d4473e8eee..01281a5336cf 100644
--- a/arch/arm64/include/asm/arch_gicv3.h
+++ b/arch/arm64/include/asm/arch_gicv3.h
@@ -190,5 +190,10 @@ static inline void gic_arch_enable_irqs(void)
 	asm volatile ("msr daifclr, #3" : : : "memory");
 }
 
+static inline bool gic_has_relaxed_pmr_sync(void)
+{
+	return cpus_have_cap(ARM64_HAS_GIC_PRIO_RELAXED_SYNC);
+}
+
 #endif /* __ASSEMBLY__ */
 #endif /* __ASM_ARCH_GICV3_H */
diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 2cfc4245d2e2..3dd8982a9ce3 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -11,6 +11,8 @@
 
 #include <linux/kasan-checks.h>
 
+#include <asm/alternative-macros.h>
+
 #define __nops(n)	".rept	" #n "\nnop\n.endr\n"
 #define nops(n)		asm volatile(__nops(n))
 
@@ -41,10 +43,11 @@
 #ifdef CONFIG_ARM64_PSEUDO_NMI
 #define pmr_sync()						\
 	do {							\
-		extern struct static_key_false gic_pmr_sync;	\
-								\
-		if (static_branch_unlikely(&gic_pmr_sync))	\
-			dsb(sy);				\
+		asm volatile(					\
+		ALTERNATIVE_CB("dsb sy",			\
+			       ARM64_HAS_GIC_PRIO_RELAXED_SYNC,	\
+			       alt_cb_patch_nops)		\
+		);						\
 	} while(0)
 #else
 #define pmr_sync()	do {} while (0)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 515975f42d03..bdabfc98226a 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2056,6 +2056,34 @@ static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
 
 	return enable_pseudo_nmi;
 }
+
+static bool has_gic_prio_relaxed_sync(const struct arm64_cpu_capabilities *entry,
+				      int scope)
+{
+	/*
+	 * If we're not using priority masking then we won't be poking PMR_EL1,
+	 * and there's no need to relax synchronization of writes to it, and
+	 * ICC_CTLR_EL1 might not be accessible and we must avoid reads from
+	 * that.
+	 *
+	 * ARM64_HAS_GIC_PRIO_MASKING has a lower index, and is a boot CPU
+	 * feature, so will be detected earlier.
+	 */
+	BUILD_BUG_ON(ARM64_HAS_GIC_PRIO_RELAXED_SYNC <= ARM64_HAS_GIC_PRIO_MASKING);
+	if (!cpus_have_cap(ARM64_HAS_GIC_PRIO_MASKING))
+		return false;
+
+	/*
+	 * When Priority Mask Hint Enable (PMHE) == 0b0, PMR is not used as a
+	 * hint for interrupt distribution, a DSB is not necessary when
+	 * unmasking IRQs via PMR, and we can relax the barrier to a NOP.
+	 *
+	 * Linux itself doesn't use 1:N distribution, so has no need to
+	 * set PMHE. The only reason to have it set is if EL3 requires it
+	 * (and we can't change it).
+	 */
+	return (gic_read_ctlr() & ICC_CTLR_EL1_PMHE_MASK) == 0;
+}
 #endif
 
 #ifdef CONFIG_ARM64_BTI
@@ -2546,6 +2574,14 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE,
 		.matches = can_use_gic_priorities,
 	},
+	{
+		/*
+		 * Depends on ARM64_HAS_GIC_PRIO_MASKING
+		 */
+		.capability = ARM64_HAS_GIC_PRIO_RELAXED_SYNC,
+		.type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE,
+		.matches = has_gic_prio_relaxed_sync,
+	},
 #endif
 #ifdef CONFIG_ARM64_E0PD
 	{
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index e2d1d3d5de1d..8427cdc0cfcb 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -311,13 +311,16 @@ alternative_else_nop_endif
 	.endif
 
 #ifdef CONFIG_ARM64_PSEUDO_NMI
-	/* Save pmr */
-alternative_if ARM64_HAS_GIC_PRIO_MASKING
+alternative_if_not ARM64_HAS_GIC_PRIO_MASKING
+	b	.Lskip_pmr_save\@
+alternative_else_nop_endif
+
 	mrs_s	x20, SYS_ICC_PMR_EL1
 	str	x20, [sp, #S_PMR_SAVE]
 	mov	x20, #GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET
 	msr_s	SYS_ICC_PMR_EL1, x20
-alternative_else_nop_endif
+
+.Lskip_pmr_save\@:
 #endif
 
 	/*
@@ -336,15 +339,19 @@ alternative_else_nop_endif
 	.endif
 
 #ifdef CONFIG_ARM64_PSEUDO_NMI
-	/* Restore pmr */
-alternative_if ARM64_HAS_GIC_PRIO_MASKING
+alternative_if_not ARM64_HAS_GIC_PRIO_MASKING
+	b	.Lskip_pmr_restore\@
+alternative_else_nop_endif
+
 	ldr	x20, [sp, #S_PMR_SAVE]
 	msr_s	SYS_ICC_PMR_EL1, x20
-	mrs_s	x21, SYS_ICC_CTLR_EL1
-	tbz	x21, #6, .L__skip_pmr_sync\@	// Check for ICC_CTLR_EL1.PMHE
-	dsb	sy				// Ensure priority change is seen by redistributor
-.L__skip_pmr_sync\@:
+
+	/* Ensure priority change is seen by redistributor */
+alternative_if_not ARM64_HAS_GIC_PRIO_RELAXED_SYNC
+	dsb	sy
 alternative_else_nop_endif
+
+.Lskip_pmr_restore\@:
 #endif
 
 	ldp	x21, x22, [sp, #S_PC]		// load ELR, SPSR
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index d0e9bb5c91fc..97e750a35f70 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -67,9 +67,7 @@ KVM_NVHE_ALIAS(__hyp_stub_vectors);
 KVM_NVHE_ALIAS(vgic_v2_cpuif_trap);
 KVM_NVHE_ALIAS(vgic_v3_cpuif_trap);
 
-/* Static key checked in pmr_sync(). */
 #ifdef CONFIG_ARM64_PSEUDO_NMI
-KVM_NVHE_ALIAS(gic_pmr_sync);
 /* Static key checked in GIC_PRIO_IRQOFF. */
 KVM_NVHE_ALIAS(gic_nonsecure_priorities);
 #endif
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index c993d43624b3..10ce8f88f86b 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -30,6 +30,7 @@ HAS_GENERIC_AUTH_ARCH_QARMA5
 HAS_GENERIC_AUTH_IMP_DEF
 HAS_GIC_CPUIF_SYSREGS
 HAS_GIC_PRIO_MASKING
+HAS_GIC_PRIO_RELAXED_SYNC
 HAS_LDAPR
 HAS_LSE_ATOMICS
 HAS_NO_FPSIMD
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 997104d4338e..3779836737c8 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -89,15 +89,6 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
  */
 static DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
 
-/*
- * Global static key controlling whether an update to PMR allowing more
- * interrupts requires to be propagated to the redistributor (DSB SY).
- * And this needs to be exported for modules to be able to enable
- * interrupts...
- */
-DEFINE_STATIC_KEY_FALSE(gic_pmr_sync);
-EXPORT_SYMBOL(gic_pmr_sync);
-
 DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
 EXPORT_SYMBOL(gic_nonsecure_priorities);
 
@@ -1768,16 +1759,8 @@ static void gic_enable_nmi_support(void)
 	for (i = 0; i < gic_data.ppi_nr; i++)
 		refcount_set(&ppi_nmi_refs[i], 0);
 
-	/*
-	 * Linux itself doesn't use 1:N distribution, so has no need to
-	 * set PMHE. The only reason to have it set is if EL3 requires it
-	 * (and we can't change it).
-	 */
-	if (gic_read_ctlr() & ICC_CTLR_EL1_PMHE_MASK)
-		static_branch_enable(&gic_pmr_sync);
-
 	pr_info("Pseudo-NMIs enabled using %s ICC_PMR_EL1 synchronisation\n",
-		static_branch_unlikely(&gic_pmr_sync) ? "forced" : "relaxed");
+		gic_has_relaxed_pmr_sync() ? "relaxed" : "forced");
 
 	/*
 	 * How priority values are used by the GIC depends on two things:
-- 
2.30.2


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[PATCH v3 5/5] arm64: irqflags: use alternative branches for pseudo-NMI logic

[Mark Rutland]

Due to the way we use alternatives in the irqflags code, even when
CONFIG_ARM64_PSEUDO_NMI=n, we generate unused alternative code for
pseudo-NMI management. This patch reworks the irqflags code to remove
the redundant code when CONFIG_ARM64_PSEUDO_NMI=n, which benefits the
more common case, and will permit further rework of our DAIF management
(e.g. in preparation for ARMv8.8-A's NMI feature).

Prior to this patch a defconfig kernel has hundreds of redundant
instructions to access ICC_PMR_EL1 (which should only need to be
manipulated in setup code), which this patch removes:

| [mark@lakrids:~/src/linux]% usekorg 12.1.0 aarch64-linux-objdump -d vmlinux-before-defconfig | grep icc_pmr_el1 | wc -l
| 885
| [mark@lakrids:~/src/linux]% usekorg 12.1.0 aarch64-linux-objdump -d vmlinux-after-defconfig | grep icc_pmr_el1 | wc -l
| 5

Those instructions alone account for more than 3KiB of kernel text, and
will be associated with additional alt_instr entries, padding and
branches, etc.

These redundant instructions exist because we use alternative sequences
for to choose between DAIF / PMR management in irqflags.h, and even when
CONFIG_ARM64_PSEUDO_NMI=n, those alternative sequences will generate the
code for PMR management, along with alt_instr entries. We use
alternatives here as this was necessary to ensure that we never
encounter a mismatched local_irq_save() ... local_irq_restore() sequence
in the middle of patching, which was possible to see if we used static
keys to choose between DAIF and PMR management.

Since commit:

  21fb26bfb01ffe0d ("arm64: alternatives: add alternative_has_feature_*()")

... we have a mechanism to use alternatives similarly to static keys,
allowing us to write the bulk of the logic in C code while also being
able to rely on all sites being patched in one go, and avoiding a
mismatched mismatched local_irq_save() ... local_irq_restore() sequence
during patching.

This patch rewrites arm64's local_irq_*() functions to use alternative
branches. This allows for the pseudo-NMI code to be entirely elided when
CONFIG_ARM64_PSEUDO_NMI=n, making a defconfig Image 64KiB smaller, and
not affectint the size of an Image with CONFIG_ARM64_PSEUDO_NMI=y:

| [mark@lakrids:~/src/linux]% ls -al vmlinux-*
| -rwxr-xr-x 1 mark mark 137473432 Jan 18 11:11 vmlinux-after-defconfig
| -rwxr-xr-x 1 mark mark 137918776 Jan 18 11:15 vmlinux-after-pnmi
| -rwxr-xr-x 1 mark mark 137380152 Jan 18 11:03 vmlinux-before-defconfig
| -rwxr-xr-x 1 mark mark 137523704 Jan 18 11:08 vmlinux-before-pnmi
| [mark@lakrids:~/src/linux]% ls -al Image-*
| -rw-r--r-- 1 mark mark 38646272 Jan 18 11:11 Image-after-defconfig
| -rw-r--r-- 1 mark mark 38777344 Jan 18 11:14 Image-after-pnmi
| -rw-r--r-- 1 mark mark 38711808 Jan 18 11:03 Image-before-defconfig
| -rw-r--r-- 1 mark mark 38777344 Jan 18 11:08 Image-before-pnmi

Some sensitive code depends on being run with interrupts enabled or with
interrupts disabled, and so when enabling or disabling interrupts we
must ensure that the compiler does not move such code around the actual
enable/disable. Before this patch, that was ensured by the combined asm
volatile blocks having memory clobbers (and any sensitive code either
being asm volatile, or touching memory). This patch consistently uses
explicit barrier() operations before and after the enable/disable, which
allows us to use the usual sysreg accessors (which are asm volatile) to
manipulate the interrupt masks. The use of pmr_sync() is pulled within
this critical section for consistency.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/irqflags.h | 191 +++++++++++++++++++++---------
 1 file changed, 132 insertions(+), 59 deletions(-)

diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
index f51653fb90e4..e0f5f6b73edd 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -21,43 +21,77 @@
  * exceptions should be unmasked.
  */
 
-/*
- * CPU interrupt mask handling.
- */
-static inline void arch_local_irq_enable(void)
+static __always_inline bool __irqflags_uses_pmr(void)
 {
-	if (system_has_prio_mask_debugging()) {
-		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
+	return IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) &&
+	       alternative_has_feature_unlikely(ARM64_HAS_GIC_PRIO_MASKING);
+}
 
+static __always_inline void __daif_local_irq_enable(void)
+{
+	barrier();
+	asm volatile("msr daifclr, #3");
+	barrier();
+}
+
+static __always_inline void __pmr_local_irq_enable(void)
+{
+	if (IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING)) {
+		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
 		WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
 	}
 
-	asm volatile(ALTERNATIVE(
-		"msr	daifclr, #3		// arch_local_irq_enable",
-		__msr_s(SYS_ICC_PMR_EL1, "%0"),
-		ARM64_HAS_GIC_PRIO_MASKING)
-		:
-		: "r" ((unsigned long) GIC_PRIO_IRQON)
-		: "memory");
-
+	barrier();
+	write_sysreg_s(GIC_PRIO_IRQON, SYS_ICC_PMR_EL1);
 	pmr_sync();
+	barrier();
 }
 
-static inline void arch_local_irq_disable(void)
+static inline void arch_local_irq_enable(void)
 {
-	if (system_has_prio_mask_debugging()) {
-		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
+	if (__irqflags_uses_pmr()) {
+		__pmr_local_irq_enable();
+	} else {
+		__daif_local_irq_enable();
+	}
+}
 
+static __always_inline void __daif_local_irq_disable(void)
+{
+	barrier();
+	asm volatile("msr daifset, #3");
+	barrier();
+}
+
+static __always_inline void __pmr_local_irq_disable(void)
+{
+	if (IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING)) {
+		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
 		WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
 	}
 
-	asm volatile(ALTERNATIVE(
-		"msr	daifset, #3		// arch_local_irq_disable",
-		__msr_s(SYS_ICC_PMR_EL1, "%0"),
-		ARM64_HAS_GIC_PRIO_MASKING)
-		:
-		: "r" ((unsigned long) GIC_PRIO_IRQOFF)
-		: "memory");
+	barrier();
+	write_sysreg_s(GIC_PRIO_IRQOFF, SYS_ICC_PMR_EL1);
+	barrier();
+}
+
+static inline void arch_local_irq_disable(void)
+{
+	if (__irqflags_uses_pmr()) {
+		__pmr_local_irq_disable();
+	} else {
+		__daif_local_irq_disable();
+	}
+}
+
+static __always_inline unsigned long __daif_local_save_flags(void)
+{
+	return read_sysreg(daif);
+}
+
+static __always_inline unsigned long __pmr_local_save_flags(void)
+{
+	return read_sysreg_s(SYS_ICC_PMR_EL1);
 }
 
 /*
@@ -65,69 +99,108 @@ static inline void arch_local_irq_disable(void)
  */
 static inline unsigned long arch_local_save_flags(void)
 {
-	unsigned long flags;
+	if (__irqflags_uses_pmr()) {
+		return __pmr_local_save_flags();
+	} else {
+		return __daif_local_save_flags();
+	}
+}
 
-	asm volatile(ALTERNATIVE(
-		"mrs	%0, daif",
-		__mrs_s("%0", SYS_ICC_PMR_EL1),
-		ARM64_HAS_GIC_PRIO_MASKING)
-		: "=&r" (flags)
-		:
-		: "memory");
+static __always_inline bool __daif_irqs_disabled_flags(unsigned long flags)
+{
+	return flags & PSR_I_BIT;
+}
 
-	return flags;
+static __always_inline bool __pmr_irqs_disabled_flags(unsigned long flags)
+{
+	return flags != GIC_PRIO_IRQON;
 }
 
-static inline int arch_irqs_disabled_flags(unsigned long flags)
+static inline bool arch_irqs_disabled_flags(unsigned long flags)
 {
-	int res;
+	if (__irqflags_uses_pmr()) {
+		return __pmr_irqs_disabled_flags(flags);
+	} else {
+		return __daif_irqs_disabled_flags(flags);
+	}
+}
 
-	asm volatile(ALTERNATIVE(
-		"and	%w0, %w1, #" __stringify(PSR_I_BIT),
-		"eor	%w0, %w1, #" __stringify(GIC_PRIO_IRQON),
-		ARM64_HAS_GIC_PRIO_MASKING)
-		: "=&r" (res)
-		: "r" ((int) flags)
-		: "memory");
+static __always_inline bool __daif_irqs_disabled(void)
+{
+	return __daif_irqs_disabled_flags(__daif_local_save_flags());
+}
 
-	return res;
+static __always_inline bool __pmr_irqs_disabled(void)
+{
+	return __pmr_irqs_disabled_flags(__pmr_local_save_flags());
 }
 
-static inline int arch_irqs_disabled(void)
+static inline bool arch_irqs_disabled(void)
 {
-	return arch_irqs_disabled_flags(arch_local_save_flags());
+	if (__irqflags_uses_pmr()) {
+		return __pmr_irqs_disabled();
+	} else {
+		return __daif_irqs_disabled();
+	}
 }
 
-static inline unsigned long arch_local_irq_save(void)
+static __always_inline unsigned long __daif_local_irq_save(void)
 {
-	unsigned long flags;
+	unsigned long flags = __daif_local_save_flags();
+
+	__daif_local_irq_disable();
+
+	return flags;
+}
 
-	flags = arch_local_save_flags();
+static __always_inline unsigned long __pmr_local_irq_save(void)
+{
+	unsigned long flags = __pmr_local_save_flags();
 
 	/*
 	 * There are too many states with IRQs disabled, just keep the current
 	 * state if interrupts are already disabled/masked.
 	 */
-	if (!arch_irqs_disabled_flags(flags))
-		arch_local_irq_disable();
+	if (!__pmr_irqs_disabled_flags(flags))
+		__pmr_local_irq_disable();
 
 	return flags;
 }
 
+static inline unsigned long arch_local_irq_save(void)
+{
+	if (__irqflags_uses_pmr()) {
+		return __pmr_local_irq_save();
+	} else {
+		return __daif_local_irq_save();
+	}
+}
+
+static __always_inline void __daif_local_irq_restore(unsigned long flags)
+{
+	barrier();
+	write_sysreg(flags, daif);
+	barrier();
+}
+
+static __always_inline void __pmr_local_irq_restore(unsigned long flags)
+{
+	barrier();
+	write_sysreg_s(flags, SYS_ICC_PMR_EL1);
+	pmr_sync();
+	barrier();
+}
+
 /*
  * restore saved IRQ state
  */
 static inline void arch_local_irq_restore(unsigned long flags)
 {
-	asm volatile(ALTERNATIVE(
-		"msr	daif, %0",
-		__msr_s(SYS_ICC_PMR_EL1, "%0"),
-		ARM64_HAS_GIC_PRIO_MASKING)
-		:
-		: "r" (flags)
-		: "memory");
-
-	pmr_sync();
+	if (__irqflags_uses_pmr()) {
+		__pmr_local_irq_restore(flags);
+	} else {
+		__daif_local_irq_restore(flags);
+	}
 }
 
 #endif /* __ASM_IRQFLAGS_H */
-- 
2.30.2


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Re: [PATCH v3 0/5] arm64: pseudo-nmi: elide code when CONFIG_ARM64_PSEUDO_NMI=n

[Catalin Marinas]

On Mon, 30 Jan 2023 14:54:24 +0000, Mark Rutland wrote:
> This series addresses a couple of sub-optimal code generation issues with
> arm64's pseudo-nmi support code:
> 
> * Even when CONFIG_ARM64_PSEUDO_NMI=n, we generate alternative code
>   sequences and alt_instr entries which will never be used. This series
>   reworks the irqflags code to use alternative branches (with an
>   IS_ENABLED() check), which allows the alternatives to be elided when
>   CONFIG_ARM64_PSEUDO_NMI=n.
> 
> [...]

Applied to arm64 (for-next/pseudo-nmi), thanks!

[1/5] arm64: rename ARM64_HAS_SYSREG_GIC_CPUIF to ARM64_HAS_GIC_CPUIF_SYSREGS
      https://git.kernel.org/arm64/c/0e62ccb9598d
[2/5] arm64: rename ARM64_HAS_IRQ_PRIO_MASKING to ARM64_HAS_GIC_PRIO_MASKING
      https://git.kernel.org/arm64/c/c888b7bd916c
[3/5] arm64: make ARM64_HAS_GIC_PRIO_MASKING depend on ARM64_HAS_GIC_CPUIF_SYSREGS
      https://git.kernel.org/arm64/c/4b43f1cd70df
[4/5] arm64: add ARM64_HAS_GIC_PRIO_RELAXED_SYNC cpucap
      https://git.kernel.org/arm64/c/8bf0a8048b15
[5/5] arm64: irqflags: use alternative branches for pseudo-NMI logic
      https://git.kernel.org/arm64/c/a5f61cc636f4

-- 
Catalin


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