linux-kernel - Re: [PATCH v3 1/6] iommu/core: split mapping to page sizes as supported by the hardware

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Message-ID: <CAK=WgbYnV1Ghtp0Hf71L-FYjKQ-V+vznYLw-_if=HMLbq5pxPQ@mail.gmail.com>
Date:	Mon, 17 Oct 2011 11:55:53 +0200
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
Cc:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	David Brown <davidb@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stepan Moskovchenko <stepanm@...eaurora.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Hiroshi Doyu <hdoyu@...dia.com>
Subject: Re: [PATCH v3 1/6] iommu/core: split mapping to page sizes as
 supported by the hardware

On Mon, Oct 17, 2011 at 11:28 AM, Roedel, Joerg <Joerg.Roedel@....com> wrote:
> The patch looks good now. Please implement option a) and it should be
> fine.

Ok, will send in a few moments.

> I will test it on an AMD IOMMU platform. We still need someone to
> test it on VT-d.

That could be great, yeah.

Though by declaring variable-size page sizes support, we intentionally
take a very conservative approach which should effectively make this
whole logic transparent to both of the x86 implementations:

The ->map() handler of both of the AMD driver and the VT-d should be
invoked in the exact way it was invoked earlier (same order, same
parameters), because before this patch-set, all IOMMU users only
mapped page-ordered regions. With this patch-set in hand, the x86
drivers declare support for all possible page-ordered page sizes, so
the IOMMU core should just be a pass-through, and call ->map() with
the exact parameters that were provided to iommu_map().

Similarly, calls to ->unmap() should not change, because current
mainline x86 users (kvm..) only unmap a single page at a time. With
this patch set in hand, the iommu core will just trivially pass those
request through to the driver's ->unmap().

So I guess that if we can test this on AMD and see that indeed this
conservative approach works (the driver gets the same ->map() and
->unmap() calls it got before) then it should work exactly the same
with VT-d.

But having someone with a VT-d setup to test this can be great of course.

Thanks,
Ohad.
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