[PATCH v3 0/2] arm64: Relax ICC_PMR_EL1 synchronisation when possible

[PATCH v3 0/2] arm64: Relax ICC_PMR_EL1 synchronisation when possible

[Marc Zyngier]

This is a very late update on [1], fixing the 32bit compilation issue that
was present in v2, and adding an extra message in the kernel log to find out
what is going on.

[1] http://lore.kernel.org/r/20190802125208.73162-1-maz@kernel.org

Marc Zyngier (2):
  arm64: Relax ICC_PMR_EL1 accesses when ICC_CTLR_EL1.PMHE is clear
  arm64: Document ICC_CTLR_EL3.PMHE setting requirements

 Documentation/arm64/booting.rst    |  3 +++
 arch/arm64/include/asm/barrier.h   | 12 ++++++++++++
 arch/arm64/include/asm/daifflags.h |  3 ++-
 arch/arm64/include/asm/irqflags.h  | 19 ++++++++++---------
 arch/arm64/include/asm/kvm_host.h  |  3 +--
 arch/arm64/kernel/entry.S          |  6 ++++--
 arch/arm64/kvm/hyp/switch.c        |  4 ++--
 drivers/irqchip/irq-gic-v3.c       | 20 ++++++++++++++++++++
 include/linux/irqchip/arm-gic-v3.h |  2 ++
 9 files changed, 56 insertions(+), 16 deletions(-)

-- 
2.20.1

[PATCH v3 1/2] arm64: Relax ICC_PMR_EL1 accesses when ICC_CTLR_EL1.PMHE is clear

[Marc Zyngier]

The GICv3 architecture specification is incredibly misleading when it
comes to PMR and the requirement for a DSB. It turns out that this DSB
is only required if the CPU interface sends an Upstream Control
message to the redistributor in order to update the RD's view of PMR.

This message is only sent when ICC_CTLR_EL1.PMHE is set, which isn't
the case in Linux. It can still be set from EL3, so some special care
is required. But the upshot is that in the (hopefuly large) majority
of the cases, we can drop the DSB altogether.

This relies on a new static key being set if the boot CPU has PMHE
set. The drawback is that this static key has to be exported to
modules.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/barrier.h   | 12 ++++++++++++
 arch/arm64/include/asm/daifflags.h |  3 ++-
 arch/arm64/include/asm/irqflags.h  | 19 ++++++++++---------
 arch/arm64/include/asm/kvm_host.h  |  3 +--
 arch/arm64/kernel/entry.S          |  6 ++++--
 arch/arm64/kvm/hyp/switch.c        |  4 ++--
 drivers/irqchip/irq-gic-v3.c       | 20 ++++++++++++++++++++
 include/linux/irqchip/arm-gic-v3.h |  2 ++
 8 files changed, 53 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index e0e2b1946f42..7d9cc5ec4971 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -29,6 +29,18 @@
 						 SB_BARRIER_INSN"nop\n",	\
 						 ARM64_HAS_SB))
 
+#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);				\
+	} while(0)
+#else
+#define pmr_sync()	do {} while (0)
+#endif
+
 #define mb()		dsb(sy)
 #define rmb()		dsb(ld)
 #define wmb()		dsb(st)
diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
index 063c964af705..53cd5fab79a8 100644
--- a/arch/arm64/include/asm/daifflags.h
+++ b/arch/arm64/include/asm/daifflags.h
@@ -8,6 +8,7 @@
 #include <linux/irqflags.h>
 
 #include <asm/arch_gicv3.h>
+#include <asm/barrier.h>
 #include <asm/cpufeature.h>
 
 #define DAIF_PROCCTX		0
@@ -65,7 +66,7 @@ static inline void local_daif_restore(unsigned long flags)
 
 		if (system_uses_irq_prio_masking()) {
 			gic_write_pmr(GIC_PRIO_IRQON);
-			dsb(sy);
+			pmr_sync();
 		}
 	} else if (system_uses_irq_prio_masking()) {
 		u64 pmr;
diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
index 1a59f0ed1ae3..aa4b6521ef14 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -6,6 +6,7 @@
 #define __ASM_IRQFLAGS_H
 
 #include <asm/alternative.h>
+#include <asm/barrier.h>
 #include <asm/ptrace.h>
 #include <asm/sysreg.h>
 
@@ -34,14 +35,14 @@ static inline void arch_local_irq_enable(void)
 	}
 
 	asm volatile(ALTERNATIVE(
-		"msr	daifclr, #2		// arch_local_irq_enable\n"
-		"nop",
-		__msr_s(SYS_ICC_PMR_EL1, "%0")
-		"dsb	sy",
+		"msr	daifclr, #2		// arch_local_irq_enable",
+		__msr_s(SYS_ICC_PMR_EL1, "%0"),
 		ARM64_HAS_IRQ_PRIO_MASKING)
 		:
 		: "r" ((unsigned long) GIC_PRIO_IRQON)
 		: "memory");
+
+	pmr_sync();
 }
 
 static inline void arch_local_irq_disable(void)
@@ -116,14 +117,14 @@ static inline unsigned long arch_local_irq_save(void)
 static inline void arch_local_irq_restore(unsigned long flags)
 {
 	asm volatile(ALTERNATIVE(
-			"msr	daif, %0\n"
-			"nop",
-			__msr_s(SYS_ICC_PMR_EL1, "%0")
-			"dsb	sy",
-			ARM64_HAS_IRQ_PRIO_MASKING)
+		"msr	daif, %0",
+		__msr_s(SYS_ICC_PMR_EL1, "%0"),
+		ARM64_HAS_IRQ_PRIO_MASKING)
 		:
 		: "r" (flags)
 		: "memory");
+
+	pmr_sync();
 }
 
 #endif /* __ASM_IRQFLAGS_H */
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f656169db8c3..5ecb091c8576 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -600,8 +600,7 @@ static inline void kvm_arm_vhe_guest_enter(void)
 	 * local_daif_mask() already sets GIC_PRIO_PSR_I_SET, we just need a
 	 * dsb to ensure the redistributor is forwards EL2 IRQs to the CPU.
 	 */
-	if (system_uses_irq_prio_masking())
-		dsb(sy);
+	pmr_sync();
 }
 
 static inline void kvm_arm_vhe_guest_exit(void)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 84a822748c84..3e0eb4f5253b 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -269,8 +269,10 @@ alternative_else_nop_endif
 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
+	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\@:
 alternative_else_nop_endif
 
 	ldp	x21, x22, [sp, #S_PC]		// load ELR, SPSR
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index bd978ad71936..85832c5bf9f5 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -12,7 +12,7 @@
 
 #include <kvm/arm_psci.h>
 
-#include <asm/arch_gicv3.h>
+#include <asm/barrier.h>
 #include <asm/cpufeature.h>
 #include <asm/kprobes.h>
 #include <asm/kvm_asm.h>
@@ -605,7 +605,7 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
 	 */
 	if (system_uses_irq_prio_masking()) {
 		gic_write_pmr(GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET);
-		dsb(sy);
+		pmr_sync();
 	}
 
 	vcpu = kern_hyp_va(vcpu);
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 422664ac5f53..0abc5a13adaa 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -87,6 +87,15 @@ 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);
+
 /* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
 static refcount_t *ppi_nmi_refs;
 
@@ -1502,6 +1511,17 @@ 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("%s ICC_PMR_EL1 synchronisation\n",
+		static_branch_unlikely(&gic_pmr_sync) ? "Forcing" : "Relaxing");
+
 	static_branch_enable(&supports_pseudo_nmis);
 
 	if (static_branch_likely(&supports_deactivate_key))
diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
index 5cc10cf7cb3e..a0bde9e12efa 100644
--- a/include/linux/irqchip/arm-gic-v3.h
+++ b/include/linux/irqchip/arm-gic-v3.h
@@ -487,6 +487,8 @@
 #define ICC_CTLR_EL1_EOImode_MASK	(1 << ICC_CTLR_EL1_EOImode_SHIFT)
 #define ICC_CTLR_EL1_CBPR_SHIFT		0
 #define ICC_CTLR_EL1_CBPR_MASK		(1 << ICC_CTLR_EL1_CBPR_SHIFT)
+#define ICC_CTLR_EL1_PMHE_SHIFT		6
+#define ICC_CTLR_EL1_PMHE_MASK		(1 << ICC_CTLR_EL1_PMHE_SHIFT)
 #define ICC_CTLR_EL1_PRI_BITS_SHIFT	8
 #define ICC_CTLR_EL1_PRI_BITS_MASK	(0x7 << ICC_CTLR_EL1_PRI_BITS_SHIFT)
 #define ICC_CTLR_EL1_ID_BITS_SHIFT	11
-- 
2.20.1

[PATCH v3 2/2] arm64: Document ICC_CTLR_EL3.PMHE setting requirements

[Marc Zyngier]

It goes without saying, but better saying it: the kernel expects
ICC_CTLR_EL3.PMHE to have the same value across all CPUs, and
for that setting not to change during the lifetime of the kernel.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/arm64/booting.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
index d3f3a60fbf25..5d78a6f5b0ae 100644
--- a/Documentation/arm64/booting.rst
+++ b/Documentation/arm64/booting.rst
@@ -213,6 +213,9 @@ Before jumping into the kernel, the following conditions must be met:
 
       - ICC_SRE_EL3.Enable (bit 3) must be initialiased to 0b1.
       - ICC_SRE_EL3.SRE (bit 0) must be initialised to 0b1.
+      - 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.
 
   - If the kernel is entered at EL1:
 
-- 
2.20.1

Re: [PATCH v3 0/2] arm64: Relax ICC_PMR_EL1 synchronisation when possible

[Catalin Marinas]

On Wed, Oct 02, 2019 at 10:06:11AM +0100, Marc Zyngier wrote:
> This is a very late update on [1], fixing the 32bit compilation issue that
> was present in v2, and adding an extra message in the kernel log to find out
> what is going on.
> 
> [1] http://lore.kernel.org/r/20190802125208.73162-1-maz@kernel.org
> 
> Marc Zyngier (2):
>   arm64: Relax ICC_PMR_EL1 accesses when ICC_CTLR_EL1.PMHE is clear
>   arm64: Document ICC_CTLR_EL3.PMHE setting requirements

Queued for 5.5. Thanks.

-- 
Catalin

Re: [PATCH v3 1/2] arm64: Relax ICC_PMR_EL1 accesses when ICC_CTLR_EL1.PMHE is clear

[liwei (GF)]

Hi Marc,

On 2019/10/2 17:06, Marc Zyngier wrote:
> The GICv3 architecture specification is incredibly misleading when it
> comes to PMR and the requirement for a DSB. It turns out that this DSB
> is only required if the CPU interface sends an Upstream Control
> message to the redistributor in order to update the RD's view of PMR.
> 
> This message is only sent when ICC_CTLR_EL1.PMHE is set, which isn't
> the case in Linux. It can still be set from EL3, so some special care
> is required. But the upshot is that in the (hopefuly large) majority
> of the cases, we can drop the DSB altogether.
> 
> This relies on a new static key being set if the boot CPU has PMHE
> set. The drawback is that this static key has to be exported to
> modules.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: James Morse <james.morse@arm.com>
> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/include/asm/barrier.h   | 12 ++++++++++++
>  arch/arm64/include/asm/daifflags.h |  3 ++-
>  arch/arm64/include/asm/irqflags.h  | 19 ++++++++++---------
>  arch/arm64/include/asm/kvm_host.h  |  3 +--
>  arch/arm64/kernel/entry.S          |  6 ++++--
>  arch/arm64/kvm/hyp/switch.c        |  4 ++--
>  drivers/irqchip/irq-gic-v3.c       | 20 ++++++++++++++++++++
>  include/linux/irqchip/arm-gic-v3.h |  2 ++
>  8 files changed, 53 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> index e0e2b1946f42..7d9cc5ec4971 100644
> --- a/arch/arm64/include/asm/barrier.h
> +++ b/arch/arm64/include/asm/barrier.h
> @@ -29,6 +29,18 @@
>  						 SB_BARRIER_INSN"nop\n",	\
>  						 ARM64_HAS_SB))
>  
> +#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);				\
> +	} while(0)
> +#else
> +#define pmr_sync()	do {} while (0)
> +#endif
> +

Thank you for solving this problem, it helps a lot indeed.

The pmr_sync() will call dsb(sy) when ARM64_PSEUDO_NMI=y and gic_pmr_sync=force,
but if pseudo nmi is not enabled through boot option, it just take one more
redundant calling than before at the following two place.

I think change dsb(sy) to
+                       asm volatile(ALTERNATIVE("nop", "dsb sy",       \
+                               ARM64_HAS_IRQ_PRIO_MASKING)     \
+                               : : : "memory");                \
may be more appropriate.

Thanks,
Wei

>  
> @@ -34,14 +35,14 @@ static inline void arch_local_irq_enable(void)
>  	}
>  
>  	asm volatile(ALTERNATIVE(
> -		"msr	daifclr, #2		// arch_local_irq_enable\n"
> -		"nop",
> -		__msr_s(SYS_ICC_PMR_EL1, "%0")
> -		"dsb	sy",
> +		"msr	daifclr, #2		// arch_local_irq_enable",
> +		__msr_s(SYS_ICC_PMR_EL1, "%0"),
>  		ARM64_HAS_IRQ_PRIO_MASKING)
>  		:
>  		: "r" ((unsigned long) GIC_PRIO_IRQON)
>  		: "memory");
> +
> +	pmr_sync();
>  }
>  
>  static inline void arch_local_irq_disable(void)
> @@ -116,14 +117,14 @@ static inline unsigned long arch_local_irq_save(void)
>  static inline void arch_local_irq_restore(unsigned long flags)
>  {
>  	asm volatile(ALTERNATIVE(
> -			"msr	daif, %0\n"
> -			"nop",
> -			__msr_s(SYS_ICC_PMR_EL1, "%0")
> -			"dsb	sy",
> -			ARM64_HAS_IRQ_PRIO_MASKING)
> +		"msr	daif, %0",
> +		__msr_s(SYS_ICC_PMR_EL1, "%0"),
> +		ARM64_HAS_IRQ_PRIO_MASKING)
>  		:
>  		: "r" (flags)
>  		: "memory");
> +
> +	pmr_sync();
>  }
>  

Re: [PATCH v3 1/2] arm64: Relax ICC_PMR_EL1 accesses when ICC_CTLR_EL1.PMHE is clear

[Marc Zyngier]

Hi Wei,

On 2019-10-23 09:38, liwei (GF) wrote:
> Hi Marc,
>
> On 2019/10/2 17:06, Marc Zyngier wrote:
>> The GICv3 architecture specification is incredibly misleading when 
>> it
>> comes to PMR and the requirement for a DSB. It turns out that this 
>> DSB
>> is only required if the CPU interface sends an Upstream Control
>> message to the redistributor in order to update the RD's view of 
>> PMR.
>>
>> This message is only sent when ICC_CTLR_EL1.PMHE is set, which isn't
>> the case in Linux. It can still be set from EL3, so some special 
>> care
>> is required. But the upshot is that in the (hopefuly large) majority
>> of the cases, we can drop the DSB altogether.
>>
>> This relies on a new static key being set if the boot CPU has PMHE
>> set. The drawback is that this static key has to be exported to
>> modules.
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: James Morse <james.morse@arm.com>
>> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
>> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>>  arch/arm64/include/asm/barrier.h   | 12 ++++++++++++
>>  arch/arm64/include/asm/daifflags.h |  3 ++-
>>  arch/arm64/include/asm/irqflags.h  | 19 ++++++++++---------
>>  arch/arm64/include/asm/kvm_host.h  |  3 +--
>>  arch/arm64/kernel/entry.S          |  6 ++++--
>>  arch/arm64/kvm/hyp/switch.c        |  4 ++--
>>  drivers/irqchip/irq-gic-v3.c       | 20 ++++++++++++++++++++
>>  include/linux/irqchip/arm-gic-v3.h |  2 ++
>>  8 files changed, 53 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/barrier.h 
>> b/arch/arm64/include/asm/barrier.h
>> index e0e2b1946f42..7d9cc5ec4971 100644
>> --- a/arch/arm64/include/asm/barrier.h
>> +++ b/arch/arm64/include/asm/barrier.h
>> @@ -29,6 +29,18 @@
>>  						 SB_BARRIER_INSN"nop\n",	\
>>  						 ARM64_HAS_SB))
>>
>> +#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);				\
>> +	} while(0)
>> +#else
>> +#define pmr_sync()	do {} while (0)
>> +#endif
>> +
>
> Thank you for solving this problem, it helps a lot indeed.
>
> The pmr_sync() will call dsb(sy) when ARM64_PSEUDO_NMI=y and
> gic_pmr_sync=force,
> but if pseudo nmi is not enabled through boot option, it just take 
> one more
> redundant calling than before at the following two place.
>
> I think change dsb(sy) to
> +                       asm volatile(ALTERNATIVE("nop", "dsb sy",     
>  \
> +                               ARM64_HAS_IRQ_PRIO_MASKING)     \
> +                               : : : "memory");                \
> may be more appropriate.

I'm not sure I understand what you mean. The static key defaults to 
false,
so if pseudo_nmi is not enabled, this dsb(sy) is simply never executed.

Am I missing something obvious?

Thanks,

         M.

>
> Thanks,
> Wei
>
>>
>> @@ -34,14 +35,14 @@ static inline void arch_local_irq_enable(void)
>>  	}
>>
>>  	asm volatile(ALTERNATIVE(
>> -		"msr	daifclr, #2		// arch_local_irq_enable\n"
>> -		"nop",
>> -		__msr_s(SYS_ICC_PMR_EL1, "%0")
>> -		"dsb	sy",
>> +		"msr	daifclr, #2		// arch_local_irq_enable",
>> +		__msr_s(SYS_ICC_PMR_EL1, "%0"),
>>  		ARM64_HAS_IRQ_PRIO_MASKING)
>>  		:
>>  		: "r" ((unsigned long) GIC_PRIO_IRQON)
>>  		: "memory");
>> +
>> +	pmr_sync();
>>  }
>>
>>  static inline void arch_local_irq_disable(void)
>> @@ -116,14 +117,14 @@ static inline unsigned long 
>> arch_local_irq_save(void)
>>  static inline void arch_local_irq_restore(unsigned long flags)
>>  {
>>  	asm volatile(ALTERNATIVE(
>> -			"msr	daif, %0\n"
>> -			"nop",
>> -			__msr_s(SYS_ICC_PMR_EL1, "%0")
>> -			"dsb	sy",
>> -			ARM64_HAS_IRQ_PRIO_MASKING)
>> +		"msr	daif, %0",
>> +		__msr_s(SYS_ICC_PMR_EL1, "%0"),
>> +		ARM64_HAS_IRQ_PRIO_MASKING)
>>  		:
>>  		: "r" (flags)
>>  		: "memory");
>> +
>> +	pmr_sync();
>>  }
>>

-- 
Jazz is not dead. It just smells funny...

Re: [PATCH v3 1/2] arm64: Relax ICC_PMR_EL1 accesses when ICC_CTLR_EL1.PMHE is clear

[liwei (GF)]

Hi Marc,

On 2019/10/23 20:13, Marc Zyngier wrote:
> Hi Wei,
> 
> On 2019-10-23 09:38, liwei (GF) wrote:
>> Hi Marc,
>>
>> On 2019/10/2 17:06, Marc Zyngier wrote:
>>> The GICv3 architecture specification is incredibly misleading when it
>>> comes to PMR and the requirement for a DSB. It turns out that this DSB
>>> is only required if the CPU interface sends an Upstream Control
>>> message to the redistributor in order to update the RD's view of PMR.
>>>
>>> This message is only sent when ICC_CTLR_EL1.PMHE is set, which isn't
>>> the case in Linux. It can still be set from EL3, so some special care
>>> is required. But the upshot is that in the (hopefuly large) majority
>>> of the cases, we can drop the DSB altogether.
>>>
>>> This relies on a new static key being set if the boot CPU has PMHE
>>> set. The drawback is that this static key has to be exported to
>>> modules.
>>>
>>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>>> Cc: Will Deacon <will@kernel.org>
>>> Cc: James Morse <james.morse@arm.com>
>>> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
>>> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>>  arch/arm64/include/asm/barrier.h   | 12 ++++++++++++
>>>  arch/arm64/include/asm/daifflags.h |  3 ++-
>>>  arch/arm64/include/asm/irqflags.h  | 19 ++++++++++---------
>>>  arch/arm64/include/asm/kvm_host.h  |  3 +--
>>>  arch/arm64/kernel/entry.S          |  6 ++++--
>>>  arch/arm64/kvm/hyp/switch.c        |  4 ++--
>>>  drivers/irqchip/irq-gic-v3.c       | 20 ++++++++++++++++++++
>>>  include/linux/irqchip/arm-gic-v3.h |  2 ++
>>>  8 files changed, 53 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
>>> index e0e2b1946f42..7d9cc5ec4971 100644
>>> --- a/arch/arm64/include/asm/barrier.h
>>> +++ b/arch/arm64/include/asm/barrier.h
>>> @@ -29,6 +29,18 @@
>>>                           SB_BARRIER_INSN"nop\n",    \
>>>                           ARM64_HAS_SB))
>>>
>>> +#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);                \
>>> +    } while(0)
>>> +#else
>>> +#define pmr_sync()    do {} while (0)
>>> +#endif
>>> +
>>
>> Thank you for solving this problem, it helps a lot indeed.
>>
>> The pmr_sync() will call dsb(sy) when ARM64_PSEUDO_NMI=y and
>> gic_pmr_sync=force,
>> but if pseudo nmi is not enabled through boot option, it just take one more
>> redundant calling than before at the following two place.
>>
>> I think change dsb(sy) to
>> +                       asm volatile(ALTERNATIVE("nop", "dsb sy",      \
>> +                               ARM64_HAS_IRQ_PRIO_MASKING)     \
>> +                               : : : "memory");                \
>> may be more appropriate.
> 
> I'm not sure I understand what you mean. The static key defaults to false,
> so if pseudo_nmi is not enabled, this dsb(sy) is simply never executed.
> 
> Am I missing something obvious?
> 
> Thanks,
> 
>         M.
> 
You are right, my mistake. Sorry for confusing you.

Thanks,
Wei