Message-ID: <55243F4B.2090307@amd.com>
Date: Tue, 7 Apr 2015 15:34:19 -0500
From: Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>
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To: Borislav Petkov <bp@suse.de>
CC: Ingo Molnar <mingo@kernel.org>, <tglx@linutronix.de>, <mingo@redhat.com>,
        <hpa@zytor.com>, <x86@kernel.org>, <bhelgaas@google.com>,
        <linux-kernel@vger.kernel.org>, <Suravee.Suthikulpanit@amd.com>,
        <joro@8bytes.org>
Subject: Re: [PATCH] x86, aperture: Check for GART before accessing GART registers
References: <551D661D.3030000@amd.com> <20150402160634.GB8045@gmail.com>
 <551D6CF5.1010604@amd.com> <20150402165356.GE4579@pd.tnic>
 <551D7695.2010509@amd.com> <20150402171705.GF4579@pd.tnic>
 <20150402181903.GA8723@gmail.com> <5523125E.2010605@amd.com>
 <20150407123457.GA3681@pd.tnic> <5523EDC2.5080206@amd.com>
 <20150407145737.GB3681@pd.tnic>
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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

Thanks,
-Aravind.
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