On Friday 05 November 2010 16:43:33 Michael S. Tsirkin wrote:
> On Fri, Nov 05, 2010 at 10:44:19AM +0800, Sheng Yang wrote:
> > > > +};
> > > > +
> > > > +This ioctl would enable in-kernel MSI-X emulation, which would
> > > > handle MSI-X +mask bit in the kernel.
> > >
> > > What happens on repeated calls when it's already enabled?
> > > How does one disable after it's enabled?
> >
> > Suppose this should only be called once. But again would update the MMIO
> > base.
>
> So maybe add this all to documentation.
>
> > It
> > would be disabled along with device deassignment.
>
> So what are you going to do when guest enables and later disables MSIX?
> Disable assignment completely?
This device goes with PCI resources allocation, rather than IRQ assignment.
>
> > We enable it explicitly because
> > not all devices have MSI-X capability.
> >
> > > > +
> > >
> > > This is very specialized for assigned devices. I would like an
> > > interface not tied to assigned devices explicitly
> > > (even if the implementation at the moment only works
> > > for assigned devices, I can patch that in later). E.g. vhost-net would
> > > benefit from such an extension too. Maybe tie this to a special
> > > GSI and this GSI can be an assigned device or not?
> >
> > You're talking about KVM_ASSIGN_GET_MSIX_ENTRY?
>
> Yes but also, and more importantly, about KVM_ASSIGN_REG_MSIX_MMIO
> and kvm_assigned_msix_mmio really.
>
> > We can't tie it to GSI, because we
> > should also cover entries without GSI. The entry number should be fine
> > for all kinds of devices using MSI-X.
>
> I don't completely understand: entries without GSI
> never need to inject an interrupt. Why do we care
> about them? Let's pass such accesses to userspace.
>
> In any case, I think MSIX GSIs are inexpensive (we never search them
> all), so we could create GSIs for all entries if we wanted to.
All mask bit accessing controlled by kernel, in order to keep consistent.
>
> > I am not sure about what PV one would looks like.
> > I use kvm_assigned_msix_entry
> > just because it can be easily reused.
>
> Not only PV, emulated devices too. OK let's try to figure out:
>
> What happens with userspace is, we inject interrupts either through
> ioctls or eventfds. Avoiding an exit to userspace on MSIX
> access is beneficial in exactly the same way.
>
> We could have an ioctl to pass in the table addresses, and mapping
> table to relevant GSIs. For example, add kvm_msix_mmio with table
> start/end, also specify which GSIs are covered.
> Maybe ask that userspace allocate all GSIs for a table consequitively?
> Or add kvm_irq_routing_msix which is same as msi but
> also has the mmio addresses? Bonus points for avoiding the need
> to scan all table on each write. For example, don't scan at all,
> instead just set a bit in KVM, and set irq entry on the next
> interrupt only: we have KVM_MAX_MSIX_PER_DEV as 256 so maybe a small 32
> byte bitmap would be enough for this, avoding a linear scan.
>
> When we pass in kvm_msix_mmio, kvm would start registering masked state.
>
> > > > +4.48 KVM_ASSIGN_GET_MSIX_ENTRY
> > > > +
> > > > +Capability: KVM_CAP_DEVICE_MSIX_MASK
> > > > +Architectures: x86
> > > > +Type: vm ioctl
> > > > +Parameters: struct kvm_assigned_msix_entry (in and out)
> > > > +Returns: 0 on success, !0 on error
> > > > +
> > > > +struct kvm_assigned_msix_entry {
> > > > + /* Assigned device's ID */
> > > > + __u32 assigned_dev_id;
> > > > + /* Ignored */
> > > > + __u32 gsi;
> > > > + /* The index of entry in the MSI-X table */
> > > > + __u16 entry;
> > > > + /* Querying flags and returning status */
> > > > + __u16 flags;
> > > > + /* Must be 0 */
> > > > + __u16 padding[2];
> > > > +};
> > > > +
> > > > +This ioctl would allow userspace to get the status of one specific
> > > > MSI-X +entry. Currently we support mask bit status querying.
> > > > +
> > > >
> > > > 5. The kvm_run structure
> > > >
> > > > Application code obtains a pointer to the kvm_run structure by
> > > >
> > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > > index f3f86b2..8fd5121 100644
> > > > --- a/arch/x86/kvm/x86.c
> > > > +++ b/arch/x86/kvm/x86.c
> > > > @@ -1926,6 +1926,7 @@ int kvm_dev_ioctl_check_extension(long ext)
> > > >
> > > > case KVM_CAP_DEBUGREGS:
> > > > case KVM_CAP_X86_ROBUST_SINGLESTEP:
> > > >
> > > > case KVM_CAP_XSAVE:
> > > > + case KVM_CAP_DEVICE_MSIX_MASK:
> > > > r = 1;
> > > > break;
> > > >
> > > > case KVM_CAP_COALESCED_MMIO:
> > > > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> > > > index 919ae53..eafafb1 100644
> > > > --- a/include/linux/kvm.h
> > > > +++ b/include/linux/kvm.h
> > > > @@ -540,6 +540,9 @@ struct kvm_ppc_pvinfo {
> > > >
> > > > #endif
> > > > #define KVM_CAP_PPC_GET_PVINFO 57
> > > > #define KVM_CAP_PPC_IRQ_LEVEL 58
> > > >
> > > > +#ifdef __KVM_HAVE_MSIX
> > > > +#define KVM_CAP_DEVICE_MSIX_MASK 59
> > > > +#endif
> > >
> > > We seem to have these HAVE macros all over.
> > > Avi, what's the idea? Let's drop them?
> >
> > Um? This kind of marcos are used here to avoid vendor specific string in
> > the header file.
>
> Am I the only one that dislikes the ifdefs we have all over this code then?
> Rest of linux tries to keep ifdefs local by stubbing functionality out.
>
> > > > + BUG_ON(adev->msix_mmio_base == 0);
> > >
> > > Below I see
> > >
> > > adev->msix_mmio_base = msix_mmio->base_addr;
> > >
> > > which comes from userspace. BUG_ON is an unfriendly way to
> > > tell user about a bug in qemu.
> > >
> > > Anyway, I don't think we should special-case 0 gpa.
> > > It's up to the user where to base the table.
> > > Use a separate flag to signal that table was initialized.
> >
> > Base_addr can't be 0 in any case. Only the unimplemented BAR are
> > hardwired to zero.
>
> No, the PCI spec does not say so. Check it out: the unimplemented BAR
> is hardwired to zero but implemented can be set to 0 as well.
OK, OK, OK, I would add one more flag.
>
> > Also if we get here with base_addr = 0, it is surely a bug.
> >
> > > > +
> > > > + return -EINVAL;
> > > > +}
> > > > +
> > > > +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)) {
> > > > + r = -EOPNOTSUPP;
> > > > + goto out;
> > > > + }
> > > > + if ((addr & 0x3) || len != 4)
> > > > + goto out;
> > > > +
> > > > + idx = msix_get_enabled_idx(adev, addr, len);
> > > > + if (idx < 0) {
> > > > + idx = (addr - adev->msix_mmio_base) /
> > > > PCI_MSIX_ENTRY_SIZE;
> > > > + if ((addr % PCI_MSIX_ENTRY_SIZE) ==
> > > > + PCI_MSIX_ENTRY_VECTOR_CTRL)
> > > > + *(unsigned long *)val =
> > > > + test_bit(idx, adev->msix_mask_bitmap) ?
> > > > + PCI_MSIX_ENTRY_CTRL_MASKBIT : 0;
> > >
> > > I suspect this is wrong for big endian platforms: PCI returns
> > > all values in little endian format.
> >
> > Let big endian platform take care of it later... There is only x86 has
> > __KVM_HAVE_MSIX now.
>
> Well it's easier to make the code correct when you write it than later.
Go back to me if someone want to implement MSI device assignment on big-endian
machine.
> > > > + else
> > > > + r = -EOPNOTSUPP;
> > > > + goto out;
> > > > + }
> > > > +
> > > > + r = kvm_get_irq_routing_entry(adev->kvm,
> > > > + adev->guest_msix_entries[idx].vector, &e);
> > > > + if (r || e.type != KVM_IRQ_ROUTING_MSI) {
> > > > + printk(KERN_WARNING "KVM: Wrong MSI-X routing entry! "
> > > > + "idx %d, addr 0x%llx, len %d\n", idx, addr,
> > > > len);
> > >
> > > Can a malicious userspace trigger this intentionally?
> >
> > No.
>
> Here's a scenario: bind an MSIX routing entry to device, then later
> change its type to regular interrupt. Fills the log with warnings,
> doesn't it?
Does QEmu suppose to discard the old routing?
> > > > + r = -EOPNOTSUPP;
> > > > + goto out;
> > > > + }
> > > > + entry[0] = e.msi.address_lo;
> > > > + entry[1] = e.msi.address_hi;
> > > > + entry[2] = e.msi.data;
> > > > + entry[3] = test_bit(adev->guest_msix_entries[idx].entry,
> > > > + adev->msix_mask_bitmap);
> > >
> > > I suspect this is wrong for big endian platforms: PCI returns
> > > all values in little endian format.
> > >
> > > > + memcpy(val, &entry[addr % PCI_MSIX_ENTRY_SIZE / 4
> > >
> > > 4 is sizeof *entry?
> >
> > 4 elements.
> > In fact "PCI_MSIX_ENTRY_SIZE / sizeof u32".
>
> Are you sure? This does not make sense to me. address in bytes, we
> take offset from start of entry in bytes, to figure which dword we need
> we divide by size of dword. No?
I've corrected this one.
--
regards
Yang, Sheng
>
> > > ], 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;
> > >
> > > I suspect this is wrong for big endian platforms: PCI returns
> > > all values in little endian format.
> > >
> > > > +
> > > > + mutex_lock(&adev->kvm->lock);
> > > > + if (!msix_mmio_in_range(adev, addr, len)) {
> > > > + r = -EOPNOTSUPP;
> > > > + goto out;
> > > > + }
> > > > + if ((addr & 0x3) || len != 4)
> > > > + goto out;
> > > > +
> > > > + idx = msix_get_enabled_idx(adev, addr, len);
> > > > + if (idx < 0) {
> > > > + idx = (addr - adev->msix_mmio_base) /
> > > > PCI_MSIX_ENTRY_SIZE;
> > > > + if (((addr % PCI_MSIX_ENTRY_SIZE) ==
> > > > + PCI_MSIX_ENTRY_VECTOR_CTRL)) {
> > > > + if (new_val & ~PCI_MSIX_ENTRY_CTRL_MASKBIT)
> > > > + goto out;
> > > > + if (new_val & PCI_MSIX_ENTRY_CTRL_MASKBIT)
> > > > + set_bit(idx, adev->msix_mask_bitmap);
> > > > + else
> > > > + clear_bit(idx, adev->msix_mask_bitmap);
> > > > + } else
> > > > + /* Userspace would handle other MMIO writing */
> > > > + r = -EOPNOTSUPP;
> > > > + goto out;
> > > > + }
> > > > + if (addr % PCI_MSIX_ENTRY_SIZE != PCI_MSIX_ENTRY_VECTOR_CTRL) {
> > > > + r = -EOPNOTSUPP;
> > > > + goto out;
> > > > + }
> > > > + if (new_val & ~PCI_MSIX_ENTRY_CTRL_MASKBIT)
> > > > + goto out;
> > > > + update_msix_mask(adev, idx, !!(new_val &
> > > > PCI_MSIX_ENTRY_CTRL_MASKBIT)); +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,
> > > > +};
> > > > +
> > > > +static int kvm_vm_ioctl_register_msix_mmio(struct kvm *kvm,
> > > > + struct kvm_assigned_msix_mmio
> > > > *msix_mmio)
> > > > +{
> > > > + int r = 0;
> > > > + struct kvm_assigned_dev_kernel *adev;
> > > > +
> > > > + mutex_lock(&kvm->lock);
> > > > + adev = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
> > > > + msix_mmio->assigned_dev_id);
> > > > + if (!adev) {
> > > > + r = -EINVAL;
> > > > + goto out;
> > > > + }
> > > > + if (msix_mmio->base_addr == 0) {
> > > > + r = -EINVAL;
> > > > + goto out;
> > > > + }
> > > > +
> > > > + mutex_lock(&kvm->slots_lock);
> > > > + if (adev->msix_mmio_base == 0) {
> > >
> > > What does this do? Handles case we are already registered?
> > > Also ! adev->msix_mmio_base
> >
> > We don't need to register again. Just update the address.
> >
> > Well, msix_mmio_base is an address. I think ==0 is more properly.
>
> Yes, there's a test above that validates for 0 and returns EINVAL.
> But using a separate flag that userspace can not control
> to mean 'already registered' will make the code clearer.
>
> > --
> > regards
> > Yang, Sheng
> >
> > > > + kvm_iodevice_init(&adev->msix_mmio_dev, &msix_mmio_ops);
> > > > + r = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS,
> > > > + &adev->msix_mmio_dev);
> > > > + if (r)
> > > > + goto out2;
> > > > + }
> > > > +
> > > > + adev->msix_mmio_base = msix_mmio->base_addr;
> > > > +out2:
> > > > + mutex_unlock(&kvm->slots_lock);
> > > > +out:
> > > > + mutex_unlock(&kvm->lock);
> > > > +
> > > > + return r;
> > > > +}
> > > >
> > > > #endif
> > > >
> > > > long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,
> > > >
> > > > @@ -812,6 +1065,36 @@ long kvm_vm_ioctl_assigned_device(struct kvm
> > > > *kvm, unsigned ioctl,
> > > >
> > > > goto out;
> > > >
> > > > break;
> > > >
> > > > }
> > > >
> > > > + case KVM_ASSIGN_GET_MSIX_ENTRY: {
> > > > + struct kvm_assigned_msix_entry entry;
> > > > + r = -EFAULT;
> > > > + if (copy_from_user(&entry, argp, sizeof entry))
> > > > + goto out;
> > > > + r = kvm_vm_ioctl_get_msix_entry(kvm, &entry);
> > > > + if (r)
> > > > + goto out;
> > > > + r = -EFAULT;
> > > > + if (copy_to_user(argp, &entry, sizeof entry))
> > > > + goto out;
> > > > + r = 0;
> > > > + break;
> > > > + }
> > > > + case KVM_ASSIGN_REG_MSIX_MMIO: {
> > > > + struct kvm_assigned_msix_mmio msix_mmio;
> > > > +
> > > > + r = -EFAULT;
> > > > + if (copy_from_user(&msix_mmio, argp, sizeof(msix_mmio)))
> > > > + goto out;
> > > > +
> > > > + r = -EINVAL;
> > > > + if (msix_mmio.flags != 0 || msix_mmio.reserved != 0)
> > > > + goto out;
> > > > +
> > > > + r = kvm_vm_ioctl_register_msix_mmio(kvm, &msix_mmio);
> > > > + if (r)
> > > > + goto out;
> > > > + break;
> > > > + }
> > > >
> > > > #endif
> > > >
> > > > }
> > > >
> > > > out:
--
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