Re: [PATCH 2/3] KVM: Emulate MSI-X table in kernel

[Sheng Yang <sheng@linux.intel.com>]

On Mon, Jan 31, 2011 at 03:09:09PM +0200, Avi Kivity wrote:
> On 01/30/2011 06:38 AM, Sheng Yang wrote:
> >(Sorry, missed this mail...)
> >
> >On Mon, Jan 17, 2011 at 02:29:44PM +0200, Avi Kivity wrote:
> >>  On 01/06/2011 12:19 PM, Sheng Yang wrote:
> >>  >Then we can support mask bit operation of assigned devices now.
> >>  >
> >>  >
> >>  >
> >>  >+int kvm_assigned_device_update_msix_mask_bit(struct kvm *kvm,
> >>  >+				int assigned_dev_id, int entry, bool mask)
> >>  >+{
> >>  >+	int r = -EFAULT;
> >>  >+	struct kvm_assigned_dev_kernel *adev;
> >>  >+	int i;
> >>  >+
> >>  >+	if (!irqchip_in_kernel(kvm))
> >>  >+		return r;
> >>  >+
> >>  >+	mutex_lock(&kvm->lock);
> >>  >+	adev = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
> >>  >+				      assigned_dev_id);
> >>  >+	if (!adev)
> >>  >+		goto out;
> >>  >+
> >>  >+	for (i = 0; i<   adev->entries_nr; i++)
> >>  >+		if (adev->host_msix_entries[i].entry == entry) {
> >>  >+			if (mask)
> >>  >+				disable_irq_nosync(
> >>  >+					adev->host_msix_entries[i].vector);
> >>
> >>  Is it okay to call disable_irq_nosync() here?  IIRC we don't check
> >>  the mask bit on irq delivery, so we may forward an interrupt to the
> >>  guest after the mask bit was set.
> >>
> >>  What does pci say about the mask bit?  when does it take effect?
> >>
> >>  Another question is whether disable_irq_nosync() actually programs
> >>  the device mask bit, or not.  If it does, then it's slow, and it may
> >>  be better to leave interrupts enabled but have an internal pending
> >>  bit.  If it doesn't program the mask bit, it's fine.
> >
> >I think Michael and Jan had explained this.
> >>
> >>  >+			else
> >>  >+				enable_irq(adev->host_msix_entries[i].vector);
> >>  >+			r = 0;
> >>  >+			break;
> >>  >+		}
> >>  >+out:
> >>  >+	mutex_unlock(&kvm->lock);
> >>  >+	return r;
> >>  >+}
> >>  >
> >>  >+
> >>  >+static int msix_table_mmio_read(struct kvm_io_device *this, gpa_t addr, int len,
> >>  >+				void *val)
> >>  >+{
> >>  >+	struct kvm_msix_mmio_dev *mmio_dev =
> >>  >+		container_of(this, struct kvm_msix_mmio_dev, table_dev);
> >>  >+	struct kvm_msix_mmio *mmio;
> >>  >+	int idx, ret = 0, entry, offset, r;
> >>  >+
> >>  >+	mutex_lock(&mmio_dev->lock);
> >>  >+	idx = get_mmio_table_index(mmio_dev, addr, len);
> >>  >+	if (idx<   0) {
> >>  >+		ret = -EOPNOTSUPP;
> >>  >+		goto out;
> >>  >+	}
> >>  >+	if ((addr&   0x3) || (len != 4&&   len != 8))
> >>  >+		goto out;
> >>  >+
> >>  >+	offset = addr&   0xf;
> >>  >+	if (offset == PCI_MSIX_ENTRY_VECTOR_CTRL&&   len == 8)
> >>  >+		goto out;
> >>  >+
> >>  >+	mmio =&mmio_dev->mmio[idx];
> >>  >+	entry = (addr - mmio->table_base_addr) / PCI_MSIX_ENTRY_SIZE;
> >>  >+	r = copy_from_user(val, (void __user *)(mmio->table_base_va +
> >>  >+			entry * PCI_MSIX_ENTRY_SIZE + offset), len);
> >>  >+	if (r)
> >>  >+		goto out;
> >>
> >>  and return ret == 0?
> >
> >Yes. This operation should be handled by in-kernel MSI-X MMIO. So we return 0
> >in order to omit this action. We can add warning to it later.
> 
> But it failed.  We need to return -EFAULT.

So it would return to QEmu. OK, let QEmu prints warning about it.

-- 
regards
Yang, Sheng
> 
> >The same as above.
> >>
> >>  >+
> >>  >+	if ((offset<   PCI_MSIX_ENTRY_VECTOR_CTRL&&   len == 4) ||
> >>  >+	    (offset<   PCI_MSIX_ENTRY_DATA&&   len == 8))
> >>  >+		ret = -ENOTSYNC;
> >>
> >>  goto out?
> >
> >No. This judgement only check if MSI data/address was touched. And the line
> >below would check if we need to operate mask bit. Because in theory guest can
> >use len=8 to modify MSI-X data and ctrl at the same time.
> >
> 
> Ok, makes sense.
> 
> -- 
> error compiling committee.c: too many arguments to function
>