linux-kernel - Re: [PATCH 1/2] powerpc: iommu: Bring back table group release

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Message-ID: <20240126154427.GB50608@ziepe.ca>
Date: Fri, 26 Jan 2024 11:44:27 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Timothy Pearson <tpearson@...torengineering.com>
Cc: Shivaprasad G Bhat <sbhat@...ux.ibm.com>, iommu <iommu@...ts.linux.dev>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Michael Ellerman <mpe@...erman.id.au>, npiggin <npiggin@...il.com>,
	christophe leroy <christophe.leroy@...roup.eu>,
	aneesh kumar <aneesh.kumar@...nel.org>,
	naveen n rao <naveen.n.rao@...ux.ibm.com>,
	jroedel <jroedel@...e.de>, aik <aik@....com>,
	bgray <bgray@...ux.ibm.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	gbatra <gbatra@...ux.vnet.ibm.com>, vaibhav <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH 1/2] powerpc: iommu: Bring back table group
 release_ownership() call

On Fri, Jan 26, 2024 at 09:39:56AM -0600, Timothy Pearson wrote:
> > Just forget about the weird KVM and SPAPR stuff, leave it under the
> > kconfig of the old code and nobody will run it. Almost nobody already
> > runs it, apparently.
> 
> We actually use QEMU/KVM/VFIO extensively at Raptor, so need the
> support and need it to be performant...

I wonder if you alone are the "almost" :)

The KVM entanglement was hairy and scary. I never did figure out what
was really going on there. Maybe you don't need all of it and can be
successful with a more typical iommu working model?

Suggest to tackle it after getting the first parts done.

Jason