Re: [Qemu-devel] [PATCH] vfio-pci: Fix Nvidia MSI ACK through 0x88000 quirk

[Dave Airlie]

On Tue, Nov 12, 2013 at 7:43 AM, Alex Williamson
<address@hidden> wrote:
> When MSI is enabled on Nvidia GeForce cards the driver seems to
> acknowledge the interrupt by writing a 0xff byte to the MSI capability
> ID register using the PCI config space mirror at offset 0x88000 from
> BAR0.  Without this, the device will only fire a single interrupt.
> VFIO handles the PCI capability ID/next registers as virtual w/o write
> support, so any write through config space is currently dropped.  Add
> a check for this and allow the write through the BAR window.  The
> registers are read-only anyway.

This is only half the truth, I'm afraid if I'm right its much worse than that.

At least on some GPUs the MSI ack is done via PCI config space itself,
and on some its done via the mirror, and yes it matters on some cards
which way it works.

Dave.