linux-kernel - Re: [PATCH 5/5] memremap: provide a not device managed memremap

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Date:   Tue, 13 Aug 2019 10:26:11 +0530
From:   Bharata B Rao <bharata@...ux.ibm.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH 5/5] memremap: provide a not device managed memremap_pages

On Mon, Aug 12, 2019 at 05:00:12PM +0200, Christoph Hellwig wrote:
> On Mon, Aug 12, 2019 at 08:20:58PM +0530, Bharata B Rao wrote:
> > On Sun, Aug 11, 2019 at 10:12:47AM +0200, Christoph Hellwig wrote:
> > > The kvmppc ultravisor code wants a device private memory pool that is
> > > system wide and not attached to a device.  Instead of faking up one
> > > provide a low-level memremap_pages for it.  Note that this function is
> > > not exported, and doesn't have a cleanup routine associated with it to
> > > discourage use from more driver like users.
> > 
> > The kvmppc secure pages management code will be part of kvm-hv which
> > can be built as module too. So it would require memremap_pages() to be
> > exported.
> > 
> > Additionally, non-dev version of the cleanup routine
> > devm_memremap_pages_release() or equivalent would also be requried.
> > With device being present, put_device() used to take care of this
> > cleanup.
> 
> Oh well.  We can add them fairly easily if we really need to, but I
> tried to avoid that.  Can you try to see if this works non-modular
> for you for now until we hear more feedback from Dan?

Yes, this patchset works non-modular and with kvm-hv as module, it
works with devm_memremap_pages_release() and release_mem_region() in the
cleanup path. The cleanup path will be required in the non-modular
case too for proper recovery from failures.

Regards,
Bharata.