linux-kernel - Re: [PATCH] x86, aperture: Check for GART before accessing GART registers

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Date:	Wed, 8 Apr 2015 09:25:48 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>,
	Jörg Rödel <joro@...tes.org>
Cc:	Ingo Molnar <mingo@...nel.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	bhelgaas@...gle.com, linux-kernel@...r.kernel.org,
	Suravee.Suthikulpanit@....com
Subject: Re: [PATCH] x86, aperture: Check for GART before accessing GART
 registers

On Tue, Apr 07, 2015 at 03:34:19PM -0500, Aravind Gopalakrishnan wrote:
> On 4/7/2015 9:57 AM, Borislav Petkov wrote:
> >On Tue, Apr 07, 2015 at 09:46:26AM -0500, Aravind Gopalakrishnan wrote:
> >>Okay. I'll do that and correct the typos Ingo pointed out earlier and
> >>resend.
> >Btw, I think you should do the same in early_gart_iommu_check() too.
> >
> >Doing the testing this way would mean that we first are testing for GART
> >hw presence and then do the rest of checks. If no GART hw, the rest of
> >the checks are meaningless.
> >
> >Also, when testing do a "pci=noearly" boot which should make
> >
> >	!early_pci_allowed()
> >
> >true and thus test that path too.
> >
> 
> Here are results from further testing:
> 1. on platforms with both iommu and gart
>     - with pci=noearly, we break out of init routines in aperture_64.c
> early. amd_iommu_init() will run through it's init routine.
>         - if amd_iommu_init() fails somewhere, we fall back to
> gart_iommu_init()
>         - gart_iommu_init() fails since gart_iommu_aperture is not set.
>         - fall back to swiotlb.
>     - with amd_iommu=off
>         - init routines in aperture_64.c run fine as both amd_gart_present()
> and early_pci_allowed() are true
>         -  amd_iommu_detect() fails due to command line arg.
>         - fall back to gart iommu
>     - with pci=noearly and amd_iommu=off
>         - break out of aperture_64.c init routines, and amd_iommu_detect()
> fails.
>         - fall back to swiotlb
> 
> 2. on platform with no gart but iommu present,
>     - pci=noearly option is not relevant as we break before that due to
> !amd_gart_present()
>     - if amd_iommu_init() fails somewhere, we fall back to swiotlb, else use
> iommu
> 
> 3. on platforms with no gart and no iommu
>     - use swiotlb regardless of any command line options passed

I don't see anything out of the ordinary but then again I don't know
this code so...

@joro, can you please double-check?

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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