RE: [PATCH 5/5] vfio-pci: Allow to mmap MSI-X table if interrupt remapping is supported

[Tian, Kevin]

> From: Tian, Kevin
> Sent: Friday, May 13, 2016 10:33 AM
> 
> > means.  The MSI-X vector table of a device is always considered
> > untrusted which is why we require user opt-ins to subvert that
> > protection.  Thanks,
> >
> 
> I only partially agree with this statement since there is different
> trust level for kernel space driver and user space driver.
> 
> OS may choose to trust kernel space driver then it can enable IRQ
> remapping only for load balance purpose w/o source id verfification.
> In such case MSI-X vector table is trusted and fully under kernel
> control. Allowing to mmap MSI-X table in user space definitely
> breaks that boundary.
> 
> Anyway my point is simple. Let's ignore how Linux kernel implements
> IRQ remapping on x86 (which may change time to time), and just
> focus on architectural possibility. Non-x86 platform may implement
> IRQ remapping completely separate from device side, then checking
> availability of IRQ remapping is enough to decide whether mmap
> MSI-X table is safe. x86 with VT-d can be configured to a mode
> requiring host control of both MSI-X entry and IRQ remapping hardware
> (without source id check). In such case it's insufficient to make
> decision simply based on IRQ remapping availability. We need a way
> to query from IRQ remapping module whether it's actually safe to
> mmap MSI-X.
> 

Or another way is to have VFIO explicitly request intel-iommu to
enforce sid check when IRQ remapping is enabled...

Thanks
Kevin