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

Marc Zyngier
2017-05-22T17:52:33Z

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).

>> +
>> + 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)?

>> +}
>> +
>> +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?

Thanks,

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