linux-kernel - Re: [PATCH v3 56/59] KVM: arm/arm64: GICv4: Prevent heterogenous systems from using GICv4

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Message-ID: <bcd17108-b035-a95f-67a4-4433e2be20ae@arm.com>
Date:   Wed, 30 Aug 2017 17:03:51 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Christoffer Dall <cdall@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Eric Auger <eric.auger@...hat.com>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v3 56/59] KVM: arm/arm64: GICv4: Prevent heterogenous
 systems from using GICv4

On 28/08/17 19:35, Christoffer Dall wrote:
> On Mon, Jul 31, 2017 at 06:26:34PM +0100, Marc Zyngier wrote:
>> The GICv4 architecture doesn't prevent CPUs implementing GICv4 to
>> cohabit with CPUs limited to GICv3 in the same system.
>>
>> This is mad (the sheduler would have to be made aware of the v4
> 
> *scheduler
> 
>> capability), and we're certainly not going to support this any
>> time soon. So let's check that all online CPUs are GICv4 capable,
>> and disable the functionnality if not.
> 
> *functionality
> 
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
>> ---
>>  include/linux/irqchip/arm-gic-v3.h |  2 ++
>>  virt/kvm/arm/vgic/vgic-v3.c        | 22 +++++++++++++++++++++-
>>  2 files changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>> index 1ea576c8126f..dfa4a51643d6 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -532,6 +532,8 @@
>>  #define ICH_VTR_SEIS_MASK		(1 << ICH_VTR_SEIS_SHIFT)
>>  #define ICH_VTR_A3V_SHIFT		21
>>  #define ICH_VTR_A3V_MASK		(1 << ICH_VTR_A3V_SHIFT)
>> +#define ICH_VTR_nV4_SHIFT		20
>> +#define ICH_VTR_nV4_MASK		(1 << ICH_VTR_nV4_SHIFT)
>>  
>>  #define ICC_IAR1_EL1_SPURIOUS		0x3ff
>>  
>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
>> index 405733678c2f..252268e83ade 100644
>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>> @@ -466,6 +466,18 @@ static int __init early_gicv4_enable(char *buf)
>>  }
>>  early_param("kvm-arm.vgic_v4_enable", early_gicv4_enable);
>>  
>> +static void vgic_check_v4_cpuif(void *param)
>> +{
>> +	u32 ich_vtr_el2 = kvm_call_hyp(__vgic_v3_get_ich_vtr_el2);
>> +	bool *v4 = param, this_cpu_is_v4;
>> +
>> +	this_cpu_is_v4 = !(ich_vtr_el2 & ICH_VTR_nV4_MASK);
>> +	if (!this_cpu_is_v4)
>> +		kvm_info("CPU%d is not GICv4 capable\n", smp_processor_id());
>> +
>> +	*v4 &= this_cpu_is_v4;
> 
> nit: You could make this function look slightly less scary by declaring
> this_cpu_is_v4 on a separate line and not use a bitwise operator on a
> boolean type.  Actually, having a function called 'check' with a side
> effect is not the nicest thing either, so why not just return what this
> particular CPU does and do the comparison in the calling loop.

Fair enough.

> #bikeshedding

How about this on top:

diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
index 01eaf4ee2f63..e471750dc0a1 100644
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c
@@ -469,18 +469,16 @@ early_param("kvm-arm.vgic_v4_enable", early_gicv4_enable);
 static void vgic_check_v4_cpuif(void *param)
 {
 	u32 ich_vtr_el2 = kvm_call_hyp(__vgic_v3_get_ich_vtr_el2);
-	bool *v4 = param, this_cpu_is_v4;
+	bool *v4 = param;
 
-	this_cpu_is_v4 = !(ich_vtr_el2 & ICH_VTR_nV4_MASK);
-	if (!this_cpu_is_v4)
+	*v4 = !(ich_vtr_el2 & ICH_VTR_nV4_MASK);
+	if (!*v4)
 		kvm_info("CPU%d is not GICv4 capable\n", smp_processor_id());
-
-	*v4 &= this_cpu_is_v4;
 }
 
 /**
  * vgic_v3_probe - probe for a GICv3 compatible interrupt controller in DT
- * @node:	pointer to the DT node
+ * @info:	pointer to the firmware-agnostic GIC information
  *
  * Returns 0 if a GICv3 has been found, returns an error code otherwise
  */
@@ -504,9 +502,14 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
 	if (info->has_v4) {
 		int cpu;
 
-		for_each_online_cpu(cpu)
+		for_each_online_cpu(cpu) {
+			bool enable;
+
 			smp_call_function_single(cpu, vgic_check_v4_cpuif,
-						 &gicv4_enable, 1);
+						 &enable, 1);
+			gicv4_enable = gicv4_enable && enable;
+		}
+
 		kvm_vgic_global_state.has_gicv4 = gicv4_enable;
 		kvm_info("GICv4 support %sabled\n",
 			 gicv4_enable ? "en" : "dis");

Thanks,

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