linux-kernel - Re: [RFC PATCH 1/3] powerpc/pseries/iommu: Bring back userspace view for single level TCE tables

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Date: Fri, 22 Mar 2024 16:49:43 +1100
From: Michael Ellerman <mpe@...erman.id.au>
To: Jason Gunthorpe <jgg@...pe.ca>, Shivaprasad G Bhat <sbhat@...ux.ibm.com>
Cc: tpearson@...torengineering.com, alex.williamson@...hat.com,
 linuxppc-dev@...ts.ozlabs.org, npiggin@...il.com,
 christophe.leroy@...roup.eu, aneesh.kumar@...nel.org,
 naveen.n.rao@...ux.ibm.com, gbatra@...ux.vnet.ibm.com,
 brking@...ux.vnet.ibm.com, aik@...abs.ru, robh@...nel.org,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org, aik@....com,
 msuchanek@...e.de, jroedel@...e.de, vaibhav@...ux.ibm.com,
 svaidy@...ux.ibm.com
Subject: Re: [RFC PATCH 1/3] powerpc/pseries/iommu: Bring back userspace
 view for single level TCE tables

Jason Gunthorpe <jgg@...pe.ca> writes:
> On Tue, Mar 12, 2024 at 01:14:20PM -0500, Shivaprasad G Bhat wrote:
>> The commit 090bad39b237a ("powerpc/powernv: Add indirect levels to
>> it_userspace") which implemented the tce indirect levels
>> support for PowerNV ended up removing the single level support
>> which existed by default(generic tce_iommu_userspace_view_alloc/free()
>> calls). On pSeries the TCEs are single level, and the allocation
>> of userspace view is lost with the removal of generic code.
>
> :( :(
>
> If this has been broken since 2018 and nobody cared till now can we
> please go in a direction of moving this code to the new iommu APIs
> instead of doubling down on more of this old stuff that apparently
> almost nobody cares about ??

It's broken *on pseries* (Linux as a guest), but it works fine on
powernv (aka bare metal, aka Linux as Hypervisor).

What's changed is folks are now testing it on pseries with Linux as a
nested hypervisor.

cheers