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

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Message-ID: <20150402171705.GF4579@pd.tnic>
Date:	Thu, 2 Apr 2015 19:17:05 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>
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, joro@...tes.org
Subject: Re: [PATCH] x86, aperture: Check for GART before accessing GART
 registers

On Thu, Apr 02, 2015 at 12:04:21PM -0500, Aravind Gopalakrishnan wrote:
> >No need - I can amend the local copy I have here.

Here's what I did:

---
From: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
Date: Wed, 1 Apr 2015 09:32:08 -0500
Subject: [PATCH] x86/gart: Check for GART support before accessing GART
 registers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

GART registers are not present in newer AMD processors (Fam15h,
Model 10h and later). So, avoid accesses to GART registers in PCI
config space by returning early in early_gart_iommu_check() and
gart_iommu_hole_init() if GART is not available.

Current code doesn't break on existing processors but there are some
side effects:

We get bogus AGP aperture messages which are simply noise on
GART-less processors:

  AGP: Node 0: aperture [bus addr 0x00000000-0x01ffffff] (32MB)
  AGP: Your BIOS doesn't leave a aperture memory hole
  AGP: Please enable the IOMMU option in the BIOS setup
  AGP: This costs you 64MB of RAM
  AGP: Mapping aperture over RAM [mem 0xd4000000-0xd7ffffff]

We can avoid calling allocate_aperture() and would not have to
wastefully reserve 64MB of RAM with memblock_reserve(). Also, we can
avoid having to loop through all PCI buses and devices twice, searching
for a non-existent AGP bridge if we bail out early.

Refactor the family check used in amd_nb into an inline function so we
can use it here as well as in amd_nb.c.

Tested the patch on Fam10h and Fam15h Model 00h-fh and this code runs
fine. On Fam15h, Models 60h-6fh and on Fam16h, we bail out early as they
don't have a GART.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
Reviewed-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc: Jörg Rödel <joro@...tes.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: x86-ml <x86@...nel.org>
Link: http://lkml.kernel.org/r/1427898728-3434-1-git-send-email-Aravind.Gopalakrishnan@amd.com
Signed-off-by: 
---
 arch/x86/include/asm/amd_nb.h | 11 +++++++++++
 arch/x86/kernel/amd_nb.c      |  4 +---
 arch/x86/kernel/aperture_64.c |  4 ++--
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/amd_nb.h b/arch/x86/include/asm/amd_nb.h
index aaac3b2fb746..864c8bd8cbe4 100644
--- a/arch/x86/include/asm/amd_nb.h
+++ b/arch/x86/include/asm/amd_nb.h
@@ -98,11 +98,22 @@ static inline u16 amd_get_node_id(struct pci_dev *pdev)
 	return 0;
 }
 
+static inline bool amd_gart_present(void)
+{
+	/* GART present only on Fam15h upto model 0fh */
+	if (boot_cpu_data.x86 == 0xf || boot_cpu_data.x86 == 0x10 ||
+	    (boot_cpu_data.x86 == 0x15 && boot_cpu_data.x86_model < 0x10))
+		return true;
+
+	return false;
+}
+
 #else
 
 #define amd_nb_num(x)		0
 #define amd_nb_has_feature(x)	false
 #define node_to_amd_nb(x)	NULL
+#define amd_gart_present(x)	false
 
 #endif
 
diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c
index 5caed1dd7ccf..29fa475ec518 100644
--- a/arch/x86/kernel/amd_nb.c
+++ b/arch/x86/kernel/amd_nb.c
@@ -89,9 +89,7 @@ int amd_cache_northbridges(void)
 			next_northbridge(link, amd_nb_link_ids);
 	}
 
-	/* GART present only on Fam15h upto model 0fh */
-	if (boot_cpu_data.x86 == 0xf || boot_cpu_data.x86 == 0x10 ||
-	    (boot_cpu_data.x86 == 0x15 && boot_cpu_data.x86_model < 0x10))
+	if (amd_gart_present())
 		amd_northbridges.flags |= AMD_NB_GART;
 
 	/*
diff --git a/arch/x86/kernel/aperture_64.c b/arch/x86/kernel/aperture_64.c
index 76164e173a24..1cb170b06853 100644
--- a/arch/x86/kernel/aperture_64.c
+++ b/arch/x86/kernel/aperture_64.c
@@ -262,7 +262,7 @@ void __init early_gart_iommu_check(void)
 	u64 aper_base = 0, last_aper_base = 0;
 	int aper_enabled = 0, last_aper_enabled = 0, last_valid = 0;
 
-	if (!early_pci_allowed())
+	if (!early_pci_allowed() || !amd_gart_present())
 		return;
 
 	/* This is mostly duplicate of iommu_hole_init */
@@ -356,7 +356,7 @@ int __init gart_iommu_hole_init(void)
 	int i, node;
 
 	if (gart_iommu_aperture_disabled || !fix_aperture ||
-	    !early_pci_allowed())
+	    !early_pci_allowed() || !amd_gart_present())
 		return -ENODEV;
 
 	pr_info("Checking aperture...\n");
-- 
2.3.3

-- 
Regards/Gruss,
    Boris.

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