Re: [PATCH 13/31] KVM: arm64: vgic-v3: Add ICV_IAR1_EL1 handler

[Auger Eric <eric.auger@redhat.com>]

Hi Marc,

On 22/05/2017 19:52, Marc Zyngier wrote:
> Hi Eric,
> 
> On 18/05/17 08:41, Auger Eric wrote:
>> Hi Marc,
>>
>> On 03/05/2017 12:45, Marc Zyngier wrote:
>>> Add a handler for reading the guest's view of the ICC_IAR1_EL1
>>> register. This involves finding the highest priority Group-1
>>> interrupt, checking against both PMR and the active group
>>> priority, activating the interrupt and setting the group
>>> priority as active.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>> ---
>>>  include/linux/irqchip/arm-gic-v3.h |   1 +
>>>  virt/kvm/arm/hyp/vgic-v3-sr.c      | 134 +++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 135 insertions(+)
>>>
>>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>>> index 97cbca19430d..7610ea4e8337 100644
>>> --- a/include/linux/irqchip/arm-gic-v3.h
>>> +++ b/include/linux/irqchip/arm-gic-v3.h
>>> @@ -391,6 +391,7 @@
>>>  #define ICH_LR_PHYS_ID_SHIFT		32
>>>  #define ICH_LR_PHYS_ID_MASK		(0x3ffULL << ICH_LR_PHYS_ID_SHIFT)
>>>  #define ICH_LR_PRIORITY_SHIFT		48
>>> +#define ICH_LR_PRIORITY_MASK		(0xffULL << ICH_LR_PRIORITY_SHIFT)
>>>  
>>>  /* These are for GICv2 emulation only */
>>>  #define GICH_LR_VIRTUALID		(0x3ffUL << 0)
>>> diff --git a/virt/kvm/arm/hyp/vgic-v3-sr.c b/virt/kvm/arm/hyp/vgic-v3-sr.c
>>> index 473ef22508e6..49aad1de3ac8 100644
>>> --- a/virt/kvm/arm/hyp/vgic-v3-sr.c
>>> +++ b/virt/kvm/arm/hyp/vgic-v3-sr.c
>>> @@ -375,6 +375,77 @@ void __hyp_text __vgic_v3_write_vmcr(u32 vmcr)
>>>  
>>>  #ifdef CONFIG_ARM64
>>>  
>>> +static int __hyp_text __vgic_v3_get_group(struct kvm_vcpu *vcpu)
>>> +{
>>> +	u32 esr = kvm_vcpu_get_hsr(vcpu);
>>> +	u8 crm = (esr & ESR_ELx_SYS64_ISS_CRM_MASK) >> ESR_ELx_SYS64_ISS_CRM_SHIFT;
>>> +
>>> +	return crm != 8;
>>> +}
>>> +
>>> +#define GICv3_IDLE_PRIORITY	0xff
>>> +
>>> +static int __hyp_text __vgic_v3_highest_priority_lr(struct kvm_vcpu *vcpu,
>>> +						    u32 vmcr,
>>> +						    u64 *lr_val)
>>> +{
>>> +	unsigned int used_lrs = vcpu->arch.vgic_cpu.used_lrs;
>>> +	u8 priority = GICv3_IDLE_PRIORITY;
>>> +	int i, lr = -1;
>>> +
>>> +	for (i = 0; i < used_lrs; i++) {
>>> +		u64 val = __gic_v3_get_lr(i);
>>> +		u8 lr_prio = (val & ICH_LR_PRIORITY_MASK) >> ICH_LR_PRIORITY_SHIFT;
>>> +
>>> +		/* Not pending in the state? */
>>> +		if ((val & ICH_LR_STATE) != ICH_LR_PENDING_BIT)
>>> +			continue;
>>> +
>>> +		/* Group-0 interrupt, but Group-0 disabled? */
>>> +		if (!(val & ICH_LR_GROUP) && !(vmcr & ICH_VMCR_ENG0_MASK))
>>> +			continue;
>>> +
>>> +		/* Group-1 interrupt, but Group-1 disabled? */
>>> +		if ((val & ICH_LR_GROUP) && !(vmcr & ICH_VMCR_ENG1_MASK))
>>> +			continue;
>>> +
>>> +		/* Not the highest priority? */
>>> +		if (lr_prio >= priority)
>>> +			continue;
>>> +
>>> +		/* This is a candidate */
>>> +		priority = lr_prio;
>>> +		*lr_val = val;
>>> +		lr = i;
>>> +	}
>>> +
>>> +	if (lr == -1)
>>> +		*lr_val = ICC_IAR1_EL1_SPURIOUS;
>>> +
>>> +	return lr;
>>> +}
>>> +
>>> +static int __hyp_text __vgic_v3_get_highest_active_priority(void)
>>> +{
>>> +	u8 nr_pre_bits = vtr_to_nr_pre_bits(read_gicreg(ICH_VTR_EL2));
>>> +	u8 nr_aprs = 1 << (nr_pre_bits - 5);
>> s/nr_aprs/nr_apr_regs ?
> 
> Sure, I can do that if that helps.
> 
>>> +	u32 hap = 0;
>>> +	int i;
>>> +
>>> +	for (i = 0; i < nr_aprs; i++) {
>>> +		u32 val;
>>> +
>>> +		val  = __vgic_v3_read_ap0rn(i);
>>> +		val |= __vgic_v3_read_ap1rn(i);
>>> +		if (val)
>>> +			return (hap + __ffs(val)) << (8 - nr_pre_bits);
>> here don't we need to shift by the actual number of subpriority bits?
>> isn't nr_pre_bits the max implemented preemption bits but not
>> necessarily the actual chosen number set by bpr?
> 
> Hmmm. I don't think that works. If you did that, you could end-up in a
> bizarre situation where you can completely miss the current active
> priority. Try for example:
> 
> 	nr_pre_bits=5
> 	set BPR1=3 (5 preemption bits)
> 	read IAR, interrupt priority = 0x10, set bit 2 in AP1R0
> 	set BPR=4 (4 preemption bits)
> 
> With this setting, you've changed the active priority from being 0x10
> (with BPR1=3) to being 8. This is wrong, as this should be an invariant.
> 
> The only way to avoid this unfortunate state of affair is to always
> normalize the active priority to always be stored as if BPR had its
> smallest possible value (which happens to be nr_pre_bits).

Hum ok. I get your point now and that looks correct to me too. Maybe a
small comment for subsequent readers would avoid the same question.
> 
>>> +
>>> +		hap += 32;
>>> +	}
>>> +
>>> +	return GICv3_IDLE_PRIORITY;
>>> +}
>>> +
>>>  static unsigned int __hyp_text __vgic_v3_get_bpr0(u32 vmcr)
>>>  {
>>>  	return (vmcr & ICH_VMCR_BPR0_MASK) >> ICH_VMCR_BPR0_SHIFT;
>>> @@ -395,6 +466,66 @@ static unsigned int __hyp_text __vgic_v3_get_bpr1(u32 vmcr)
>>>  	return bpr;
>>>  }
>>>  
>> Would be nice to have a short doc comment.
>> I understand this zeros the subpriority field in the priority value, is
>> it correct? pseudocode PriorityGroup()?
> 
> Yes, I should probably add some references to the pseudocode.
> 
>>> +static u8 __hyp_text __vgic_v3_pri_to_pre(u8 pri, u32 vmcr, int grp)
>>> +{
>>> +	unsigned int bpr;
>>> +
>>> +	if (!grp)
>>> +		bpr = __vgic_v3_get_bpr0(vmcr) + 1;
>>> +	else
>>> +		bpr = __vgic_v3_get_bpr1(vmcr);
>>> +
>>> +	return pri & (GENMASK(7, 0) << bpr);
>>  & GENMASK(7, bpr)?
> 
> Not sure about that. If grp==0, bpr can range from 1 to 8. If it is 8,
> what is the meaning of GENMASK(7,8)?

OK forget it ;-)
> 
>>> +}
>>> +
>>> +static void __hyp_text __vgic_v3_set_active_priority(u8 pre)
>>> +{
>>> +	u8 nr_pre_bits = vtr_to_nr_pre_bits(read_gicreg(ICH_VTR_EL2));
>>> +	u8 hap = pre >> (8 - nr_pre_bits);
>> Could you add a comment about what is hap. I tend to think it is the
>> group priority but then I don't get why we don't shift by 8 -bpr
> 
> "hap" stands for Highest Active Priority. And for the reasons describer
> above, we need to normalize it, irrespective of the BPR.
> 
> Does it make sense?

yes it does.

So Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> 
> Thanks,
> 
> 	M.
>