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From: Matthew Rosato <mjrosato@linux.ibm.com>
To: Niklas Schnelle <schnelle@linux.ibm.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>
Cc: "Jason Gunthorpe" <jgg@ziepe.ca>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-s390@vger.kernel.org, "Pierre Morel" <pmorel@linux.ibm.com>,
	"Christian Bornträger" <borntraeger@linux.ibm.com>
Subject: Re: [PATCH v2 1/1] vfio/type1: Respect IOMMU reserved regions in vfio_test_domain_fgsp()
Date: Thu, 5 Jan 2023 11:06:31 -0500	[thread overview]
Message-ID: <dcd428a4-aaed-060e-34e0-69f931986ae6@linux.ibm.com> (raw)
In-Reply-To: <20230104154202.1152198-2-schnelle@linux.ibm.com>

On 1/4/23 10:42 AM, Niklas Schnelle wrote:
> Since commit cbf7827bc5dc ("iommu/s390: Fix potential s390_domain
> aperture shrinking") the s390 IOMMU driver uses reserved regions for the
> system provided DMA ranges of PCI devices. Previously it reduced the
> size of the IOMMU aperture and checked it on each mapping operation.
> On current machines the system denies use of DMA addresses below 2^32 for
> all PCI devices.
> 
> Usually mapping IOVAs in a reserved regions is harmless until a DMA
> actually tries to utilize the mapping. However on s390 there is
> a virtual PCI device called ISM which is implemented in firmware and
> used for cross LPAR communication. Unlike real PCI devices this device
> does not use the hardware IOMMU but inspects IOMMU translation tables
> directly on IOTLB flush (s390 RPCIT instruction). If it detects IOVA
> mappings outside the allowed ranges it goes into an error state. This
> error state then causes the device to be unavailable to the KVM guest.
> 
> Analysing this we found that vfio_test_domain_fgsp() maps 2 pages at DMA
> address 0 irrespective of the IOMMUs reserved regions. Even if usually
> harmless this seems wrong in the general case so instead go through the
> freshly updated IOVA list and try to find a range that isn't reserved,
> and fits 2 pages, is PAGE_SIZE * 2 aligned. If found use that for
> testing for fine grained super pages.
> 
> Fixes: 6fe1010d6d9c ("vfio/type1: DMA unmap chunking")
> Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>

Thanks, this fixes the issue I'm seeing with ISM.

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>



  reply	other threads:[~2023-01-05 16:06 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-04 15:42 [PATCH v2 0/1] vfio/type1: Fix vfio-pci pass-through of ISM devices Niklas Schnelle
2023-01-04 15:42 ` [PATCH v2 1/1] vfio/type1: Respect IOMMU reserved regions in vfio_test_domain_fgsp() Niklas Schnelle
2023-01-05 16:06   ` Matthew Rosato [this message]
2023-01-06 17:24   ` Alex Williamson
2023-01-06 18:03     ` Jason Gunthorpe
2023-01-09  8:49       ` Niklas Schnelle
2023-01-09  9:00     ` Niklas Schnelle

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