Re: [PATCH 7/8] KVM: assigned dev: Introduce io_device for MSI-X MMIO accessing

Sheng Yang
2010-10-21T06:45:41Z

On Wednesday 20 October 2010 17:46:47 Avi Kivity wrote:
> On 10/20/2010 10:26 AM, Sheng Yang wrote:
> > It would be work with KVM_CAP_DEVICE_MSIX_MASK, which we would enable in
> > the last patch.
> >
> >
> > +struct kvm_assigned_msix_mmio {
> > + __u32 assigned_dev_id;
> > + __u64 base_addr;
>
> Different alignment and size on 32 and 64 bits.
>
> Is base_addr a guest physical address? Do we need a size or it it fixed?

Yes it is. The size would be implicit showed when guest using
KVM_ASSIGN_SET_MSIX_ENTRY(say, entry number).

>
> > + __u32 flags;
> > + __u32 reserved[2];
> > +};
> > +
> >
> > @@ -465,6 +465,8 @@ struct kvm_assigned_dev_kernel {
> >
> > struct pci_dev *dev;
> > struct kvm *kvm;
> > spinlock_t assigned_dev_lock;
> >
> > + u64 msix_mmio_base;
>
> gpa_t.
>
> > + struct kvm_io_device msix_mmio_dev;
> >
> > };
> >
> > struct kvm_irq_mask_notifier {
> >
> > diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> > index bf96ea7..5d2adc4 100644
> > --- a/virt/kvm/assigned-dev.c
> > +++ b/virt/kvm/assigned-dev.c
> >
> > @@ -739,6 +739,137 @@ msix_entry_out:
> > return r;
> >
> > }
> >
> > +
> > +static bool msix_mmio_in_range(struct kvm_assigned_dev_kernel *adev,
> > + gpa_t addr, int len, int *idx)
> > +{
> > + int i;
> > +
> > + if (!(adev->irq_requested_type& KVM_DEV_IRQ_HOST_MSIX))
> > + return false;
>
> Just don't install the io_device in that case.

Yeah, I meant to remove this line, because entries_nr = 0 in the case.
>
> > + BUG_ON(adev->msix_mmio_base == 0);
> > + for (i = 0; i< adev->entries_nr; i++) {
> > + u64 start, end;
> > + start = adev->msix_mmio_base +
> > + adev->guest_msix_entries[i].entry * PCI_MSIX_ENTRY_SIZE;
> > + end = start + PCI_MSIX_ENTRY_SIZE;
> > + if (addr>= start&& addr + len<= end) {
> > + *idx = i;
> > + return true;
> > + }
>
> What if it's a partial hit? write part of an entry and part of another
> entry?

Can't be. The spec said the accessing must be DWORD aligned. And I forced the
checking later.
>
> > + }
> > + return false;
> > +}
> > +
> > +static int msix_mmio_read(struct kvm_io_device *this, gpa_t addr, int
> > len, + void *val)
> > +{
> > + struct kvm_assigned_dev_kernel *adev =
> > + container_of(this, struct kvm_assigned_dev_kernel,
> > + msix_mmio_dev);
> > + int idx, r = 0;
> > + u32 entry[4];
> > + struct kvm_kernel_irq_routing_entry *e;
> > +
> > + mutex_lock(&adev->kvm->lock);
> > + if (!msix_mmio_in_range(adev, addr, len,&idx)) {
> > + r = -EOPNOTSUPP;
> > + goto out;
> > + }
> > + if ((addr& 0x3) || len != 4) {
> > + printk(KERN_WARNING
> > + "KVM: Unaligned reading for device MSI-X MMIO! "
> > + "addr 0x%llx, len %d\n", addr, len);
>
> Guest exploitable printk()
>
> > + r = -EOPNOTSUPP;
>
> If the guest assigned the device to another guest, it allows the nested
> guest to kill the non-nested guest. Need to exit in a graceful fashion.

Don't understand... It wouldn't result in kill but return to QEmu/userspace.
>
> > + goto out;
> > + }
> > +
> > + e = kvm_get_irq_routing_entry(adev->kvm,
> > + adev->guest_msix_entries[idx].vector);
> > + if (!e || e->type != KVM_IRQ_ROUTING_MSI) {
> > + printk(KERN_WARNING "KVM: Wrong MSI-X routing entry! "
> > + "addr 0x%llx, len %d\n", addr, len);
> > + r = -EOPNOTSUPP;
> > + goto out;
> > + }
> > + entry[0] = e->msi.address_lo;
> > + entry[1] = e->msi.address_hi;
> > + entry[2] = e->msi.data;
> > + entry[3] = !!(adev->guest_msix_entries[idx].flags&
> > + KVM_ASSIGNED_MSIX_MASK);
> > + memcpy(val,&entry[addr % PCI_MSIX_ENTRY_SIZE / 4], len);
> > +
> > +out:
> > + mutex_unlock(&adev->kvm->lock);
> > + return r;
> > +}
> > +
> > +static int msix_mmio_write(struct kvm_io_device *this, gpa_t addr, int
> > len, + const void *val)
> > +{
> > + struct kvm_assigned_dev_kernel *adev =
> > + container_of(this, struct kvm_assigned_dev_kernel,
> > + msix_mmio_dev);
> > + int idx, r = 0;
> > + unsigned long new_val = *(unsigned long *)val;
> > + bool entry_masked;
> > +
> > + mutex_lock(&adev->kvm->lock);
> > + if (!msix_mmio_in_range(adev, addr, len,&idx)) {
> > + r = -EOPNOTSUPP;
> > + goto out;
> > + }
> > + if ((addr& 0x3) || len != 4) {
> > + printk(KERN_WARNING
> > + "KVM: Unaligned writing for device MSI-X MMIO! "
> > + "addr 0x%llx, len %d, val 0x%lx\n",
> > + addr, len, new_val);
> > + r = -EOPNOTSUPP;
> > + goto out;
> > + }
> > + entry_masked = adev->guest_msix_entries[idx].flags&
> > + KVM_ASSIGNED_MSIX_MASK;
> > + if (addr % PCI_MSIX_ENTRY_SIZE != PCI_MSIX_ENTRY_VECTOR_CTRL) {
> > + /* Only allow entry modification when entry was masked */
> > + if (!entry_masked) {
> > + printk(KERN_WARNING
> > + "KVM: guest try to write unmasked MSI-X entry. "
> > + "addr 0x%llx, len %d, val 0x%lx\n",
> > + addr, len, new_val);
> > + r = 0;
>
> What does the spec says about this situation?

As Michael pointed out. The spec said the result is "undefined" indeed.

>
> > + } else
> > + /* Leave it to QEmu */
>
> s/qemu/userspace/
>
> > + r = -EOPNOTSUPP;
>
> What would userspace do in this situation? I hope you documented
> precisely what the kernel handles and what it doesn't?
>
> I prefer more kernel code in the kernel to having an interface which is
> hard to use correctly.
>
> > + goto out;
> > + }
> > + if (new_val& ~1ul) {
>
> Is there a #define for this bit?

Sorry I didn't find it. mask_msi_irq() also use the number 1... Maybe we can add
one.

--
regards
Yang, Sheng

>
> > + printk(KERN_WARNING
> > + "KVM: Bad writing for device MSI-X MMIO! "
> > + "addr 0x%llx, len %d, val 0x%lx\n",
> > + addr, len, new_val);
> > + r = -EOPNOTSUPP;
> > + goto out;
> > + }
> > + if (new_val == 1&& !entry_masked) {
> > + adev->guest_msix_entries[idx].flags |=
> > + KVM_ASSIGNED_MSIX_MASK;
> > + update_msix_mask(adev, idx);
> > + } else if (new_val == 0&& entry_masked) {
> > + adev->guest_msix_entries[idx].flags&=
> > + ~KVM_ASSIGNED_MSIX_MASK;
> > + update_msix_mask(adev, idx);
> > + }
>
> Ah, I see you do reuse update_msix_mask().
>
> > +out:
> > + mutex_unlock(&adev->kvm->lock);
> > +
> > + return r;
> > +}
> > +
> > +static const struct kvm_io_device_ops msix_mmio_ops = {
> > + .read = msix_mmio_read,
> > + .write = msix_mmio_write,
> > +};
> > +
> >
> > #endif
> >
> > long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,