linux-kernel - Re: [PATCH 2/2] iommu/vt-d: Report superpage support in sysfs

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Message-ID: <1438612514.26511.342.camel@infradead.org>
Date:	Mon, 03 Aug 2015 15:35:14 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Joerg Roedel <joro@...tes.org>,
	Alex Williamson <alex.williamson@...hat.com>
Cc:	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iommu/vt-d: Report superpage support in sysfs

On Mon, 2015-08-03 at 16:30 +0200, Joerg Roedel wrote:
> On Tue, Jul 14, 2015 at 03:25:04PM -0600, Alex Williamson wrote:
> > We already have the VT-d capability register printed raw, but it
> > typically involves a trip to the code or the spec to figure out
> > whether superpages are supported.  Make this easier with "2M_pages"
> > and "1G_pages" sysfs entries that clearly report Y/N.
> > 
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > ---
> >  drivers/iommu/intel-iommu.c |   22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> 
> Can we make this a generic entry for all iommu types and export a
> pagesize bitmap instead?

As long as we don't further entrench the current abomination of
advertising all page sizes which are a multiple of 4KiB, which we do to
work around KVM brain damage.

I think I did manage to fix that once, with a patch that would abuse pg
->freelist when tearing down the mappings from KVM. Which ISTR was the
main problem with fixing the API. I'll see if I can recover enough of
my addled memory and revive that...

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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