On Wed, 2009-09-23 at 06:55 -0700, Greg Kroah-Hartman wrote:
> From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
>
> We are seeing a number of crashes in SMM, when VT-d is enabled while
> 'Legacy USB support' is enabled in various BIOSes.
>
> The BIOS is supposed to indicate which addresses it uses for DMA in a
> special ACPI table ("RMRR"), so that we can punch a hole for it when we
> set up the IOMMU.
>
> The problem is, as usual, that BIOS engineers are totally incompetent.
> They write code which will crash if the DMA goes AWOL, and then they
> either neglect to provide an RMRR table at all, or they put the wrong
> addresses in it. And of course they don't do _any_ QA, since that would
> take too much time away from their crack-smoking habit.
>
> The real fix, of course, is for consumers to refuse to buy motherboards
> which only have closed-source firmware available. If we had _open_
> firmware, bugs like this would be easy to fix.
>
> Since that's something I can only dream about, this patch implements an
> alternative -- ensuring that the USB controllers are handed off from the
> BIOS and quiesced _before_ the IOMMU is initialised. That would have
> been a much better design than this RMRR nonsense in the first place, of
> course. The bootloader has no business doing DMA after the OS has booted
> anyway.
>
> Signed-off-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
> ---
That was in the iommu tree when I asked Linus to pull it yesterday.
--
dwmw2
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