Re: [Xen-devel] [PATCH v3 18/39] ARM: new VGIC: Add CTLR, TYPER and IIDR handlers

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 27/03/18 21:38, Stefano Stabellini wrote:
> On Wed, 21 Mar 2018, Andre Przywara wrote:
>> Those three registers are v2 emulation specific, so their implementation
>> lives entirely in vgic-mmio-v2.c. Also they are handled in one function,
>> as their implementation is pretty simple.
>> We choose to piggy-back on the existing KVM identification registers,
>> but use a different variant (major revision).
> 
> CC'ing Marc.
> 
> Reusing the KVM product ID could cause issues, for instance we could
> clash with KVM if Linux changes the Major number. If we were to actually
> reuse KVM's PRODUCT_ID we would need a better coordination in place.

Marc is aware of this, as this approach was decided after a brief
discussion with Julien and him last week.
If we need a quirk on the (guest) GIC driver side for the KVM VGIC, KVM
would bump the revision number, not the variant.
This is a good as coordination can realistically ever get.

> I suggest to either introduce a Xen specific PRODUCT_ID,

This is a bit of a stretch. Firstly, by the nature of this port the two
implementations are really close. Secondly: we can't really just occupy
any product ID. Technically the "K" isn't even reserved, but this ship
has sailed, so we could just piggy back on that for simplicity.

> or simply reuse
> the hardware value like the old vgic does for now. We can fix this
> later.

This implementation is totally different from anything existing. And we
don't want the guest to apply any errata fixes for the particular
hardware GIC. So using the hardware ID is not the best idea.

Cheers,
Andre

> In fact, I would be happy to swith to KVM's product id after appropriate
> discussions with the KVM community. At the very least, it would need to
> be written down somewhere under docs/ and/or Documentation.
> 
> Marc, what do you think?
> 
> 
>> When the guest enables the distributor, we kick all VCPUs to get
>> potentially pending interrupts serviced.
>>
>> This is based on Linux commit 2b0cda878965, written by Marc Zyngier.
>>
>> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxx>
>> ---
>> Changelog v2 ... v3:
>> - fix misleading comment about PRODUCT_ID letter
>> - clarify on meaning of VARIANT_ID_XEN
>>
>> Changelog v1 ... v2:
>> use new IIDR values (KVM product ID, Xen revision)
>> - add comment on handling GICD enablement
>> - use new vcpu_kick() function
>>
>>  xen/arch/arm/vgic/vgic-mmio-v2.c | 63 
>> +++++++++++++++++++++++++++++++++++++++-
>>  xen/arch/arm/vgic/vgic.c         | 15 ++++++++++
>>  xen/arch/arm/vgic/vgic.h         |  9 ++++++
>>  3 files changed, 86 insertions(+), 1 deletion(-)
>>
>> diff --git a/xen/arch/arm/vgic/vgic-mmio-v2.c 
>> b/xen/arch/arm/vgic/vgic-mmio-v2.c
>> index 6f10cf16ca..43c1ab5906 100644
>> --- a/xen/arch/arm/vgic/vgic-mmio-v2.c
>> +++ b/xen/arch/arm/vgic/vgic-mmio-v2.c
>> @@ -20,9 +20,70 @@
>>  #include "vgic.h"
>>  #include "vgic-mmio.h"
>>  
>> +static unsigned long vgic_mmio_read_v2_misc(struct vcpu *vcpu,
>> +                                            paddr_t addr, unsigned int len)
>> +{
>> +    uint32_t value;
>> +
>> +    switch ( addr & 0x0c )      /* filter for the 4 registers handled here 
>> */
>> +    {
>> +    case GICD_CTLR:
>> +        value = vcpu->domain->arch.vgic.enabled ? GICD_CTL_ENABLE : 0;
>> +        break;
>> +    case GICD_TYPER:
>> +        value = vcpu->domain->arch.vgic.nr_spis + VGIC_NR_PRIVATE_IRQS;
>> +        value = (value >> 5) - 1;
>> +        value |= (vcpu->domain->max_vcpus - 1) << 5;
> 
> NIT: You can reuse GICD_TYPE_CPUS_SHIFT
> 
> 
>> +        break;
>> +    case GICD_IIDR:
>> +        value = (PRODUCT_ID_KVM << 24) |
>> +                (VARIANT_ID_XEN << 16) |
>> +                (IMPLEMENTER_ARM << 0);
>> +        break;
>> +    default:
>> +        return 0;
>> +    }
>> +
>> +    return value;
>> +}
>> +
>> +static void vgic_mmio_write_v2_misc(struct vcpu *vcpu,
>> +                                    paddr_t addr, unsigned int len,
>> +                                    unsigned long val)
>> +{
>> +    struct vgic_dist *dist = &vcpu->domain->arch.vgic;
>> +    bool enabled;
>> +
>> +    switch ( addr & 0x0c )      /* filter for the 4 registers handled here 
>> */
>> +    {
>> +    case GICD_CTLR:
>> +        domain_lock(vcpu->domain);
>> +
>> +        /*
>> +         * Store the new enabled state in our distributor structure.
>> +         * Work out whether it was disabled before and now got enabled,
>> +         * so that we signal all VCPUs to check for interrupts to be 
>> injected.
>> +         */
>> +        enabled = dist->enabled;
>> +        dist->enabled = val & GICD_CTL_ENABLE;
>> +        enabled = !enabled && dist->enabled;
>> +
>> +        domain_unlock(vcpu->domain);
>> +
>> +        if ( enabled )
>> +            vgic_kick_vcpus(vcpu->domain);
>> +
>> +        break;
>> +    case GICD_TYPER:
>> +    case GICD_IIDR:
>> +        /* read-only, writes ignored */
>> +        return;
>> +    }
>> +}
>> +
>>  static const struct vgic_register_region vgic_v2_dist_registers[] = {
>>      REGISTER_DESC_WITH_LENGTH(GICD_CTLR,
>> -        vgic_mmio_read_raz, vgic_mmio_write_wi, 12,
>> +        vgic_mmio_read_v2_misc, vgic_mmio_write_v2_misc, 12,
>>          VGIC_ACCESS_32bit),
>>      REGISTER_DESC_WITH_BITS_PER_IRQ(GICD_IGROUPR,
>>          vgic_mmio_read_rao, vgic_mmio_write_wi, 1,
>> diff --git a/xen/arch/arm/vgic/vgic.c b/xen/arch/arm/vgic/vgic.c
>> index 925cda4580..37b425a16c 100644
>> --- a/xen/arch/arm/vgic/vgic.c
>> +++ b/xen/arch/arm/vgic/vgic.c
>> @@ -684,6 +684,21 @@ int vgic_vcpu_pending_irq(struct vcpu *vcpu)
>>      return ret;
>>  }
>>  
>> +void vgic_kick_vcpus(struct domain *d)
>> +{
>> +    struct vcpu *vcpu;
>> +
>> +    /*
>> +     * We've injected an interrupt, time to find out who deserves
>> +     * a good kick...
>> +     */
>> +    for_each_vcpu( d, vcpu )
>> +    {
>> +        if ( vgic_vcpu_pending_irq(vcpu) )
>> +            vcpu_kick(vcpu);
>> +    }
>> +}
>> +
>>  /*
>>   * Local variables:
>>   * mode: C
>> diff --git a/xen/arch/arm/vgic/vgic.h b/xen/arch/arm/vgic/vgic.h
>> index 7f221fd195..aed7e4179a 100644
>> --- a/xen/arch/arm/vgic/vgic.h
>> +++ b/xen/arch/arm/vgic/vgic.h
>> @@ -17,6 +17,14 @@
>>  #ifndef __XEN_ARM_VGIC_VGIC_H__
>>  #define __XEN_ARM_VGIC_VGIC_H__
>>  
>> +/*
>> + * We piggy-back on the already used KVM product ID,  but use a different
>> + * variant (major revision) for Xen.
>> + */
>> +#define PRODUCT_ID_KVM          0x4b        /* ASCII code K */
>> +#define VARIANT_ID_XEN          0x01
>> +#define IMPLEMENTER_ARM         0x43b
>> +
>>  #define vgic_irq_is_sgi(intid) ((intid) < VGIC_NR_SGIS)
>>  
>>  static inline bool irq_is_pending(struct vgic_irq *irq)
>> @@ -37,6 +45,7 @@ struct vgic_irq *vgic_get_irq(struct domain *d, struct 
>> vcpu *vcpu,
>>  void vgic_put_irq(struct domain *d, struct vgic_irq *irq);
>>  void vgic_queue_irq_unlock(struct domain *d, struct vgic_irq *irq,
>>                             unsigned long flags);
>> +void vgic_kick_vcpus(struct domain *d);
>>  
>>  static inline void vgic_get_irq_kref(struct vgic_irq *irq)
>>  {

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