Re: [PATCH 0/9 v2] vfio-pci: add support for Freescale IOMMU (PAMU)

On Thu, 2013-11-21 at 13:43 -0700, Alex Williamson wrote:

On Thu, 2013-11-21 at 11:20 +0000, Bharat Bhushan wrote:

quoted

quoted

-----Original Message-----
From: Alex Williamson [mailto:alex.williamson@redhat.com]
Sent: Thursday, November 21, 2013 12:17 AM
To: Bhushan Bharat-R65777
Cc: joro@8bytes.org; bhelgaas@google.com; agraf@suse.de; Wood Scott-B07421;
Yoder Stuart-B08248; iommu@lists.linux-foundation.org; linux-
pci@vger.kernel.org; linuxppc-dev@lists.ozlabs.org; linux-
kernel@vger.kernel.org; Bhushan Bharat-R65777
Subject: Re: [PATCH 0/9 v2] vfio-pci: add support for Freescale IOMMU (PAMU)

Is VFIO_IOMMU_PAMU_GET_MSI_BANK_COUNT per aperture (ie. each vfio user has
$COUNT regions at their disposal exclusively)?

Number of msi-bank count is system wide and not per aperture, But will be setting windows for banks in the device aperture.
So say if we are direct assigning 2 pci device (both have different iommu group, so 2 aperture in iommu) to VM.
Now qemu can make only one call to know how many msi-banks are there but it must set sub-windows for all banks for both pci device in its respective aperture.

I'm still confused.  What I want to make sure of is that the banks are
independent per aperture.  For instance, if we have two separate
userspace processes operating independently and they both chose to use
msi bank zero for their device, that's bank zero within each aperture
and doesn't interfere.  Or another way to ask is can a malicious user
interfere with other users by using the wrong bank.  Thanks,

They can interfere.  With this hardware, the only way to prevent that is
to make sure that a bank is not shared by multiple protection contexts.
For some of our users, though, I believe preventing this is less
important than the performance benefit.

-Scott