linux-kernel - Re: [PATCH] Intel IOMMU Pass Through Support

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Date:	Sun, 19 Apr 2009 11:05:08 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Fenghua Yu <fenghua.yu@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Weidong Han <weidong.han@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	IOMMU <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH] Intel IOMMU Pass Through Support

On Wed, 2009-04-15 at 17:19 -0700, Fenghua Yu wrote:
> +       if (iommu_pass_through)
> +               if (!pass_through) {
> +                       printk(KERN_INFO
> +                               "Pass Through is not supported by hardware.\n");
> +                       iommu_pass_through = 0;
> +               }

So if we ask for pass-through and the hardware doesn't support it, we
end up in full-translation mode? Wouldn't it be better to set up 1:1
mappings for each device instead?

(We probably want to fix up the code which sets up 1:1 mappings to
actually share page tables where appropriate, and to use superpages).

Also, did we already have a discussion about whether this should be an
intel_iommu= parameter, or a generic iommu= one?

>                 ret = domain_context_mapping_one(domain,
> -                                                pci_domain_nr(parent->bus),
> -                                                parent->bus->number,
> -                                                parent->devfn);
> +                                               pci_domain_nr(parent->bus),
> +                                               parent->bus->number,
> +                                               parent->devfn, translation);

Whitespace damage here -- you're modifying continuation lines which used
to be right underneath the 'domain' parameter, and you're making them
not line up properly.

You have the same problem elsewhere for newly-added code too, in fact:

> +               ret = domain_context_mapping(domain, pdev,
> +                                               CONTEXT_TT_PASS_THROUGH);


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

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