Re: [RFC PATCH 16/45] KVM: arm/arm64: vgic-new: Add PENDING registers handlers

Andre Przywara
2016-04-11T11:29:44Z

On 31/03/16 10:35, Christoffer Dall wrote:
> On Fri, Mar 25, 2016 at 02:04:39AM +0000, Andre Przywara wrote:
>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>> ---
>> virt/kvm/arm/vgic/vgic_mmio.c | 87 ++++++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 85 insertions(+), 2 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic_mmio.c b/virt/kvm/arm/vgic/vgic_mmio.c
>> index 0688a69..8514f92 100644
>> --- a/virt/kvm/arm/vgic/vgic_mmio.c
>> +++ b/virt/kvm/arm/vgic/vgic_mmio.c
>> @@ -206,6 +206,89 @@ static int vgic_mmio_write_cenable(struct kvm_vcpu *vcpu,
>> return 0;
>> }
>>
>> +static int vgic_mmio_read_pending(struct kvm_vcpu *vcpu,
>> + struct kvm_io_device *this,
>> + gpa_t addr, int len, void *val)
>> +{
>> + struct vgic_io_device *iodev = container_of(this,
>> + struct vgic_io_device, dev);
>> + u32 intid = (addr - iodev->base_addr) * 8;
>> + u32 value = 0;
>> + int i;
>> +
>> + if (iodev->redist_vcpu)
>> + vcpu = iodev->redist_vcpu;
>> +
>> + /* Loop over all IRQs affected by this read */
>> + for (i = 0; i < len * 8; i++) {
>> + struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
>> +
>> + spin_lock(&irq->irq_lock);
>> + if (irq->pending)
>> + value |= (1U << i);
>> + spin_unlock(&irq->irq_lock);
>
> here there clearly is no need to take the lock (because a bool read is
> atomic), but that should be explained in a one-line comment.

Is that really true? Isn't it that another lock holder expects full
control over the IRQ struct, including the freedom to change values at
will without caring about other observers?
I might be too paranoid here, but I think I explicitly added the lock
here for a reason (which I don't remember anymore, sadly).

Cheers,
Andre.

>> + }
>> +
>> + write_mask32(value, addr & 3, len, val);
>> + return 0;
>> +}
>> +
>> +static int vgic_mmio_write_spending(struct kvm_vcpu *vcpu,
>> + struct kvm_io_device *this,
>> + gpa_t addr, int len, const void *val)
>> +{
>> + struct vgic_io_device *iodev = container_of(this,
>> + struct vgic_io_device, dev);
>> + u32 intid = (addr - iodev->base_addr) * 8;
>> + int i;
>> +
>> + if (iodev->redist_vcpu)
>> + vcpu = iodev->redist_vcpu;
>> +
>> + for_each_set_bit(i, val, len * 8) {
>> + struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
>> +
>> + spin_lock(&irq->irq_lock);
>> + irq->pending = true;
>> + if (irq->config == VGIC_CONFIG_LEVEL)
>> + irq->soft_pending = true;
>> +
>> + vgic_queue_irq(vcpu->kvm, irq);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int vgic_mmio_write_cpending(struct kvm_vcpu *vcpu,
>> + struct kvm_io_device *this,
>> + gpa_t addr, int len, const void *val)
>> +{
>> + struct vgic_io_device *iodev = container_of(this,
>> + struct vgic_io_device, dev);
>> + u32 intid = (addr - iodev->base_addr) * 8;
>> + int i;
>> +
>> + if (iodev->redist_vcpu)
>> + vcpu = iodev->redist_vcpu;
>> +
>> + for_each_set_bit(i, val, len * 8) {
>> + struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
>> +
>> + spin_lock(&irq->irq_lock);
>> +
>> + if (irq->config == VGIC_CONFIG_LEVEL) {
>> + irq->soft_pending = false;
>> + irq->pending = irq->line_level;
>> + } else {
>> + irq->pending = false;
>> + }
>> + /* TODO: Does the exit/entry code take care of "unqueuing"? */
>
> see previous patch comment
>
>> +
>> + spin_unlock(&irq->irq_lock);
>> + }
>> + return 0;
>> +}
>> +
>> struct vgic_register_region vgic_v2_dist_registers[] = {
>> REGISTER_DESC_WITH_LENGTH(GIC_DIST_CTRL,
>> vgic_mmio_read_v2_misc, vgic_mmio_write_v2_misc, 12),
>> @@ -216,9 +299,9 @@ struct vgic_register_region vgic_v2_dist_registers[] = {
>> REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_ENABLE_CLEAR,
>> vgic_mmio_read_enable, vgic_mmio_write_cenable, 1),
>> REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_PENDING_SET,
>> - vgic_mmio_read_nyi, vgic_mmio_write_nyi, 1),
>> + vgic_mmio_read_pending, vgic_mmio_write_spending, 1),
>> REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_PENDING_CLEAR,
>> - vgic_mmio_read_nyi, vgic_mmio_write_nyi, 1),
>> + vgic_mmio_read_pending, vgic_mmio_write_cpending, 1),
>> REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_ACTIVE_SET,
>> vgic_mmio_read_nyi, vgic_mmio_write_nyi, 1),
>> REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_ACTIVE_CLEAR,
>> --
>> 2.7.3
>>
>