linux-kernel - Re: [PATCH v8 0/3] mm/hmm/test: add self tests for HMM

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Date:   Mon, 23 Mar 2020 15:25:34 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Ralph Campbell <rcampbell@...dia.com>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v8 0/3] mm/hmm/test: add self tests for HMM

On Sun, Mar 22, 2020 at 10:10:38AM +0200, Leon Romanovsky wrote:
> On Sat, Mar 21, 2020 at 06:55:05PM -0300, Jason Gunthorpe wrote:
> > On Sat, Mar 21, 2020 at 10:27:46AM -0700, Ralph Campbell wrote:
> > >
> > > On 3/21/20 2:00 AM, Leon Romanovsky wrote:
> > > > On Fri, Mar 20, 2020 at 05:31:05PM -0700, Ralph Campbell wrote:
> > > > > This series adds basic self tests for HMM and are intended for Jason
> > > > > Gunthorpe's rdma tree which has a number of HMM patches applied.
> > > > >
> > > > > Changes v7 -> v8:
> > > > > Rebased to Jason's rdma/hmm tree, plus Jason's 6 patch series
> > > > >    "Small hmm_range_fault() cleanups".
> > > > > Applied a number of changes from Jason's comments.
> > > > >
> > > > > Changes v6 -> v7:
> > > > > Rebased to linux-5.6.0-rc6
> > > > > Reverted back to just using mmu_interval_notifier_insert() and making
> > > > >    this series only introduce HMM self tests.
> > > > >
> > > > > Changes v5 -> v6:
> > > > > Rebased to linux-5.5.0-rc6
> > > > > Refactored mmu interval notifier patches
> > > > > Converted nouveau to use the new mmu interval notifier API
> > > > >
> > > > > Changes v4 -> v5:
> > > > > Added mmu interval notifier insert/remove/update callable from the
> > > > >    invalidate() callback
> > > > > Updated HMM tests to use the new core interval notifier API
> > > > >
> > > > > Changes v1 -> v4:
> > > > > https://lore.kernel.org/linux-mm/20191104222141.5173-1-rcampbell@nvidia.com
> > > > >
> > > > > Ralph Campbell (3):
> > > > >    mm/hmm/test: add selftest driver for HMM
> > > > >    mm/hmm/test: add selftests for HMM
> > > > >    MAINTAINERS: add HMM selftests
> > > > >
> > > > >   MAINTAINERS                            |    3 +
> > > > >   include/uapi/linux/test_hmm.h          |   59 ++
> > > >
> > > > Isn't UAPI folder supposed to be for user-visible interfaces that follow
> > > > the rule of non-breaking user space and not for selftests?
> > > >
> > > > Thanks
> > > >
> > >
> > > Most of the other kernel module tests seem to invoke the test as part of the
> > > module load/init. I'm open to moving it if there is a more appropriate location.
> >
> > Is it even possible to create a user mm_struct and put crazy things in
> > it soley from a kernel module?
> 
> I didn't look very closely of what Ralph did in his patchsets, but from
> what I know, if you want in-kernel interface, you use in-kernel module,
> if you want to test user visible uapi, you write application. You don't
> create new UAPI just to test something in the kernel.

That works fine as long as the in-kernel interfaces don't require user
created objects like mm_struct and vmas, which is the case here.

So there must be some special uAPI between the kerne/user to make it
work.

Jason