linux-kernel - [PATCH v3 0/1] vfio/type1: Fix vfio-pci pass-through of ISM devices

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Message-Id: <20230110164427.4051938-1-schnelle@linux.ibm.com>
Date:   Tue, 10 Jan 2023 17:44:26 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        Christian Bornträger <borntraeger@...ux.ibm.com>
Subject: [PATCH v3 0/1] vfio/type1: Fix vfio-pci pass-through of ISM devices

Hi Alex,

This is v2 of my attempt of fixing an issue we have on s390 with vfio-pci
pass-through of the s390 specific virtual PCI device called ISM and used for
cross LPAR communication. As the patch tries to explain the fact that
vfio_test_domain_fgsp() uses an IOMMU mapping at IOVA 0 irrespective of any
reserved regions causes the ISM device to go into an error state and thus
becomes unusable for a KVM guest breaking pass-through. I tried to improve
the background and explanation compared to v1 hope its more clear now.

As for testing, I tested this based on current master on both on s390 where it
skips the reserved 0x0-0x100000000 range and on an AMD Ryzen 3990X where it
continues to do the test on DMA address 0 and sets domain->fgsp to true.

Thanks,
Niklas Schnelle

Changes since v2:
- Don't require region->start to be aligned but instead just that we can fit an
  aligned allocation (Alex)
- Use Fixes tag for the introduction of reserved regions as that came
  after the fine grained super pages test (Alex)

Changes since v1:
- Reworded commit message to hopefully explain things a bit better and
  highlight that usually just mapping but not issuing DMAs for IOVAs in
  a resverved region is harmless but still breaks things with ISM devices.
- Added a check for PAGE_SIZE * 2 alignment (Jason)

Niklas Schnelle (1):
  vfio/type1: Respect IOMMU reserved regions in vfio_test_domain_fgsp()

 drivers/vfio/vfio_iommu_type1.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

-- 
2.34.1