Re: [PATCH v3 3/5] iommu/s390: Fix potential s390_domain aperture shrinking

[Jason Gunthorpe]

On Thu, Sep 29, 2022 at 05:33:00PM +0200, Niklas Schnelle wrote:
> The s390 IOMMU driver currently sets the IOMMU domain's aperture to
> match the device specific DMA address range of the device that is first
> attached. This is not ideal. For one if the domain has no device
> attached in the meantime the aperture could be shrunk allowing
> translations outside the aperture to exist in the translation tables.
> Also this is a bit of a misuse of the aperture which really should
> describe what addresses can be translated and not some device specific
> limitations.
> 
> Instead of misusing the aperture like this we can instead create
> reserved ranges for the ranges inaccessible to the attached devices
> allowing devices with overlapping ranges to still share an IOMMU domain.
> This also significantly simplifies s390_iommu_attach_device() allowing
> us to move the aperture check to the beginning of the function and
> removing the need to hold the device list's lock to check the aperture.
> 
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> ---
>  drivers/iommu/s390-iommu.c | 50 +++++++++++++++++++++++++++-----------
>  1 file changed, 36 insertions(+), 14 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason