Re: [v2 18/25] KVM: kvm-vfio: implement the VFIO skeleton for VT-d Posted-Interrupts

[Alex Williamson]

On Mon, 2014-12-08 at 04:58 +0000, Wu, Feng wrote:
> 
> > -----Original Message-----
> > From: Eric Auger [mailto:eric.auger@xxxxxxxxxx]
> > Sent: Thursday, December 04, 2014 11:36 PM
> > To: Wu, Feng; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx;
> > x86@xxxxxxxxxx; gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> > dwmw2@xxxxxxxxxxxxx; joro@xxxxxxxxxx; alex.williamson@xxxxxxxxxx;
> > jiang.liu@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> > kvm@xxxxxxxxxxxxxxx
> > Subject: Re: [v2 18/25] KVM: kvm-vfio: implement the VFIO skeleton for VT-d
> > Posted-Interrupts
> > 
> > Hi Feng,
> > 
> > On 12/03/2014 08:39 AM, Feng Wu wrote:
> > > This patch adds the kvm-vfio interface for VT-d Posted-Interrrupts.
> > > When guests updates MSI/MSI-x information for an assigned-device,
> > update
> > > QEMU will use KVM_DEV_VFIO_DEVICE_POSTING_IRQ attribute to setup
> > > IRTE for VT-d PI. This patch implement this IRQ attribute.
> > s/implement/implements
> > >
> > > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > > ---
> > >  include/linux/kvm_host.h |   19 ++++++++
> > >  virt/kvm/vfio.c          |  103
> > ++++++++++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 122 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 5cd4420..8d06678 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -1134,6 +1134,25 @@ static inline int
> > kvm_arch_vfio_set_forward(struct kvm_fwd_irq *fwd_irq,
> > >  }
> > >  #endif
> > >
> > > +#ifdef __KVM_HAVE_ARCH_KVM_VFIO_POSTING
> > > +/*
> > > + * kvm_arch_vfio_update_pi_irte - set IRTE for Posted-Interrupts
> > > + *
> > > + * @kvm: kvm
> > > + * @host_irq: host irq of the interrupt
> > > + * @guest_irq: gsi of the interrupt
> > > + * returns 0 on success, < 0 on failure
> > > + */
> > > +int kvm_arch_vfio_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
> > > +				 uint32_t guest_irq);
> > > +#else
> > > +static int kvm_arch_vfio_update_pi_irte(struct kvm *kvm, unsigned int
> > host_irq,
> > > +					uint32_t guest_irq)
> > > +{
> > > +	return 0;
> > > +}
> > > +#endif
> > > +
> > >  #ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
> > >
> > >  static inline void kvm_vcpu_set_in_spin_loop(struct kvm_vcpu *vcpu, bool
> > val)
> > > diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> > > index 6bc7001..5e5515f 100644
> > > --- a/virt/kvm/vfio.c
> > > +++ b/virt/kvm/vfio.c
> > > @@ -446,6 +446,99 @@ out:
> > >  	return ret;
> > >  }
> > >
> > > +static int kvm_vfio_pci_get_irq_count(struct pci_dev *pdev, int irq_type)
> > > +{
> > > +	if (irq_type == VFIO_PCI_INTX_IRQ_INDEX) {
> > > +		u8 pin;
> > > +
> > > +		pci_read_config_byte(pdev, PCI_INTERRUPT_PIN, &pin);
> > > +		if (pin)
> > > +			return 1;
> > > +	} else if (irq_type == VFIO_PCI_MSI_IRQ_INDEX)
> > > +		return pci_msi_vec_count(pdev);
> > > +	else if (irq_type == VFIO_PCI_MSIX_IRQ_INDEX)
> > > +		return pci_msix_vec_count(pdev);
> > > +
> > > +	return 0;
> > > +}
> > for platform case I was asked to move the retrieval of absolute irq
> > number to the architecture specific part. I don't know if it should
> > apply to PCI stuff as well? This explains why I need to pass the VFIO
> > device (or struct device handle) to the arch specific part. Actually we
> > do the same job, we provide a phys/virt IRQ mapping to KVM, right? So to
> > me our architecture specific API should look quite similar?
> 
> In my patch, QEMU passes IRQ type(MSI/MSIx in my case), VFIO device index,
> and sub-index via "struct kvm_vfio_dev_irq" to KVM, then KVM will find the
> real host irq from the VFIO device index and the IRQ type. Is this something
> similar with your patch?
> 
> > 
> > > +
> > > +static int kvm_vfio_set_pi(struct kvm_device *kdev, int32_t __user *argp)
> > > +{
> > > +	struct kvm_vfio_dev_irq pi_info;
> > > +	uint32_t *gsi;
> > > +	unsigned long minsz;
> > > +	struct vfio_device *vdev;
> > > +	struct msi_desc *entry;
> > > +	struct device *dev;
> > > +	struct pci_dev *pdev;
> > > +	int i, max, ret;
> > > +
> > > +	minsz = offsetofend(struct kvm_vfio_dev_irq, count);
> > > +
> > > +	if (copy_from_user(&pi_info, (void __user *)argp, minsz))
> > > +		return -EFAULT;
> > > +
> > > +	if (pi_info.argsz < minsz || pi_info.index >= VFIO_PCI_NUM_IRQS)
> > PCI specific check, same remark as above but I will let Alex further
> > comment on this and possibly invalidate this commeny ;-)
> > > +		return -EINVAL;
> > > +
> > > +	vdev = kvm_vfio_get_vfio_device(pi_info.fd);
> > > +	if (IS_ERR(vdev))
> > > +		return PTR_ERR(vdev);
> > > +
> > > +	dev = kvm_vfio_external_base_device(vdev);
> > > +	if (!dev || !dev_is_pci(dev)) {
> > > +		ret = -EFAULT;
> > > +		goto put_vfio_device;
> > > +	}
> > > +
> > > +	pdev = to_pci_dev(dev);
> > > +
> > > +	max = kvm_vfio_pci_get_irq_count(pdev, pi_info.index);
> > > +	if (max <= 0) {
> > > +		ret = -EFAULT;
> > > +		goto put_vfio_device;
> > > +	}
> > > +
> > > +	if (pi_info.argsz - minsz < pi_info.count * sizeof(int) ||
> > shouldn' we use the actual datatype?
> 
> I am afraid I don't get this, could you please be more specific? Thanks a lot!

We could have a platform that supports 64bit INTs.

> > > +	    pi_info.start >= max || pi_info.start + pi_info.count > max) {
> > > +		ret = -EINVAL;
> > > +		goto put_vfio_device;
> > > +	}
> > > +
> > > +	gsi = memdup_user((void __user *)((unsigned long)argp + minsz),
> > > +			   pi_info.count * sizeof(int));
> > same question as above
> > > +	if (IS_ERR(gsi)) {
> > > +		ret = PTR_ERR(gsi);
> > > +		goto put_vfio_device;
> > > +	}
> > > +
> > > +#ifdef CONFIG_PCI_MSI
> > > +	for (i = 0; i < pi_info.count; i++) {
> > > +		list_for_each_entry(entry, &pdev->msi_list, list) {
> > > +			if (entry->msi_attrib.entry_nr != pi_info.start+i)
> > > +				continue;
> > > +
> > > +			ret = kvm_arch_vfio_update_pi_irte(kdev->kvm,
> > > +							   entry->irq,
> > > +							   gsi[i]);
> > > +			if (ret) {
> > > +				ret = -EFAULT;
> > why -EFAULT? and not propagation of original error code?
> Yes, you are right. Thanks for the comments!
> 
> > you may have posting set for part of the subindexes and unset for rest.
> > Isn't it an issue?
> 
> QEMU will always set the posting for all the sub-indexes for MSI/MSIx,
> once the guest updates the configuration of some sub-indexes, KVM will
> update it accordingly. So in which case will what you mentioned above
> happen?

QEMU is just one userspace, not necessarily the only userspace.  The
kernel shouldn't expect a specific userspace behavior.

> > > +				goto free_gsi;
> > > +			}
> > > +		}
> > > +	}
> > > +#endif
> > > +
> > > +	ret = 0;
> > > +
> > > +free_gsi:
> > > +	kfree(gsi);
> > > +
> > > +put_vfio_device:
> > > +	kvm_vfio_put_vfio_device(vdev);
> > > +	return ret;
> > > +}
> > > +
> > >  static int kvm_vfio_set_device(struct kvm_device *kdev, long attr, u64 arg)
> > >  {
> > >  	int32_t __user *argp = (int32_t __user *)(unsigned long)arg;
> > > @@ -456,6 +549,11 @@ static int kvm_vfio_set_device(struct kvm_device
> > *kdev, long attr, u64 arg)
> > >  	case KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ:
> > >  		ret = kvm_vfio_control_irq_forward(kdev, attr, argp);
> > >  		break;
> > > +#ifdef __KVM_HAVE_ARCH_KVM_VFIO_POSTING
> > > +	case KVM_DEV_VFIO_DEVICE_POSTING_IRQ:
> > > +		ret = kvm_vfio_set_pi(kdev, argp);
> > > +		break;
> > > +#endif
> > >  	default:
> > >  		ret = -ENXIO;
> > >  	}
> > > @@ -511,6 +609,11 @@ static int kvm_vfio_has_attr(struct kvm_device
> > *dev,
> > >  		case KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ:
> > >  			return 0;
> > >  #endif
> > > +#ifdef __KVM_HAVE_ARCH_KVM_VFIO_POSTING
> > > +		case KVM_DEV_VFIO_DEVICE_POSTING_IRQ:
> > > +			return 0;
> > > +#endif
> > > +
> > >  		}
> > >  		break;
> > >  	}
> > >
> 
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