Re: [PATCH v6 14/24] KVM: arm64: vgic-v3: vgic_v3_lpi_sync_pending_status

Auger Eric
2017-05-05T09:45:55Z

Hi,

On 05/05/2017 10:11, Christoffer Dall wrote:
> On Thu, May 04, 2017 at 01:44:34PM +0200, Eric Auger wrote:
>> this new helper synchronizes the irq pending_latch
>> with the LPI pending bit status found in rdist pending table.
>> As the status is consumed, we reset the bit in pending table.
>>
>> As we need the PENDBASER_ADDRESS() in vgic-v3, let's move its
>> definition in the irqchip header. We restore the full length
>> of the field, ie [51:16]. Same for PROPBASER_ADDRESS with full
>> field length of [51:12].
>
> why into irqchip and not just the vgic header file?
Well most register field shift/masks are located there. This may be
useful as well for the ITS driver if power management gets implemented
>
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>>
>> v6: new
>> ---
>> include/linux/irqchip/arm-gic-v3.h | 2 ++
>> virt/kvm/arm/vgic/vgic-its.c | 6 ++----
>> virt/kvm/arm/vgic/vgic-v3.c | 44 ++++++++++++++++++++++++++++++++++++++
>> virt/kvm/arm/vgic/vgic.h | 1 +
>> 4 files changed, 49 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>> index 9519c7b..e09e5d7 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -159,6 +159,8 @@
>> #define GICR_PROPBASER_RaWaWb GIC_BASER_CACHEABILITY(GICR_PROPBASER, INNER, RaWaWb)
>>
>> #define GICR_PROPBASER_IDBITS_MASK (0x1f)
>> +#define GICR_PROPBASER_ADDRESS(x) ((x) & GENMASK_ULL(51, 12))
>> +#define GICR_PENDBASER_ADDRESS(x) ((x) & GENMASK_ULL(51, 16))
>>
>> #define GICR_PENDBASER_SHAREABILITY_SHIFT (10)
>> #define GICR_PENDBASER_INNER_CACHEABILITY_SHIFT (7)
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index e7bb86a..f43ea30c 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -198,8 +198,6 @@ static struct its_ite *find_ite(struct vgic_its *its, u32 device_id,
>> */
>> #define BASER_ADDRESS(x) ((x) & GENMASK_ULL(47, 16))
>> #define CBASER_ADDRESS(x) ((x) & GENMASK_ULL(47, 12))
>> -#define PENDBASER_ADDRESS(x) ((x) & GENMASK_ULL(47, 16))
>> -#define PROPBASER_ADDRESS(x) ((x) & GENMASK_ULL(47, 12))
>>
>> #define GIC_LPI_OFFSET 8192
>>
>> @@ -234,7 +232,7 @@ static struct its_collection *find_collection(struct vgic_its *its, int coll_id)
>> static int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
>> struct kvm_vcpu *filter_vcpu)
>> {
>> - u64 propbase = PROPBASER_ADDRESS(kvm->arch.vgic.propbaser);
>> + u64 propbase = GICR_PROPBASER_ADDRESS(kvm->arch.vgic.propbaser);
>> u8 prop;
>> int ret;
>>
>> @@ -346,7 +344,7 @@ static u32 max_lpis_propbaser(u64 propbaser)
>> */
>> static int its_sync_lpi_pending_table(struct kvm_vcpu *vcpu)
>> {
>> - gpa_t pendbase = PENDBASER_ADDRESS(vcpu->arch.vgic_cpu.pendbaser);
>> + gpa_t pendbase = GICR_PENDBASER_ADDRESS(vcpu->arch.vgic_cpu.pendbaser);
>> struct vgic_irq *irq;
>> int last_byte_offset = -1;
>> int ret = 0;
>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
>> index be0f4c3..0d753ae 100644
>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>> @@ -252,6 +252,50 @@ void vgic_v3_enable(struct kvm_vcpu *vcpu)
>> vgic_v3->vgic_hcr = ICH_HCR_EN;
>> }
>>
>> +int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq)
>> +{
>> + struct kvm_vcpu *vcpu;
>> + int byte_offset, bit_nr;
>> + gpa_t pendbase, ptr;
>> + bool status;
>> + u8 val;
>> + int ret;
>> +
>> +retry:
>> + vcpu = irq->target_vcpu;
>> + if (!vcpu)
>> + return 0;
>> +
>> + pendbase = GICR_PENDBASER_ADDRESS(vcpu->arch.vgic_cpu.pendbaser);
>> +
>> + byte_offset = irq->intid / BITS_PER_BYTE;
>> + bit_nr = irq->intid % BITS_PER_BYTE;
>> + ptr = pendbase + byte_offset;
>> +
>> + ret = kvm_read_guest(kvm, ptr, &val, 1);
>> + if (ret)
>> + return ret;
>> +
>> + status = val & (1 << bit_nr);
>> +
>> + spin_lock(&irq->irq_lock);
>> + if (irq->target_vcpu != vcpu) {
>> + spin_unlock(&irq->irq_lock);
>> + goto retry;
>
> Can the guest be continuously changing the configuration of the LPI and
> cause this function to be called, which will efficiently hog this CPU
> from the system, or am I being overly cautious here?
Yes but on the other hand, there is a risk the target_vcpu has changed,
isn't it? So the alternative you be to return -EBUSY. and caller, ie.
its_add_lpi would return that error?
>
>> + }
>> + irq->pending_latch = status;
>> + vgic_queue_irq_unlock(vcpu->kvm, irq);
>> +
>> + if (status) {
>> + /* clear consumed data */
>> + val &= ~(1 << bit_nr);
>> + ret = kvm_write_guest(kvm, ptr, &val, 1);
>> + if (ret)
>> + return ret;
>
> Do we have a problem that if this is done twice within the same byte (on
> different LPIs) then the data could be strangely out of sync?
Not sure I get what you mean here? I reset a single bit within the byte.
Do you mean there could be a concurrency issue?

In principle we are not obliged to reset the bit, right? Why do we care?
The table will be updated on next pending table save.

Thanks

Eric

>
> Do we care?
>
>
> Thanks,
> -Christoffer
>
>> + }
>> + return 0;
>> +}
>> +
>> /* check for overlapping regions and for regions crossing the end of memory */
>> static bool vgic_v3_check_base(struct kvm *kvm)
>> {
>> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
>> index b87f1c6..309ab64 100644
>> --- a/virt/kvm/arm/vgic/vgic.h
>> +++ b/virt/kvm/arm/vgic/vgic.h
>> @@ -157,6 +157,7 @@ void vgic_v3_get_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcr);
>> void vgic_v3_enable(struct kvm_vcpu *vcpu);
>> int vgic_v3_probe(const struct gic_kvm_info *info);
>> int vgic_v3_map_resources(struct kvm *kvm);
>> +int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq);
>> int vgic_register_redist_iodevs(struct kvm *kvm, gpa_t dist_base_address);
>>
>> int vgic_register_its_iodevs(struct kvm *kvm);
>> --
>> 2.5.5
>>