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Message-ID: <tip-63ecd3b13d5cf07959a2315ec62a7c62e20df114@git.kernel.org>
Date: Mon, 5 Nov 2018 12:24:51 -0800
From: tip-bot for Borislav Petkov <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, rppt@...ux.ibm.com, bp@...e.de,
tglx@...utronix.de, hpa@...or.com, mingo@...nel.org, x86@...nel.org
Subject: [tip:x86/cleanups] x86/gart: Rewrite early_gart_iommu_check()
comment
Commit-ID: 63ecd3b13d5cf07959a2315ec62a7c62e20df114
Gitweb: https://git.kernel.org/tip/63ecd3b13d5cf07959a2315ec62a7c62e20df114
Author: Borislav Petkov <bp@...e.de>
AuthorDate: Thu, 1 Nov 2018 16:24:43 +0100
Committer: Borislav Petkov <bp@...e.de>
CommitDate: Mon, 5 Nov 2018 21:18:31 +0100
x86/gart: Rewrite early_gart_iommu_check() comment
... to actually explain what the function is trying to do.
Reported-by: Mike Rapoport <rppt@...ux.ibm.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: <x86@...nel.org>
Link: http://lkml.kernel.org/r/20181101155314.30690-1-bp@alien8.de
---
arch/x86/kernel/aperture_64.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/aperture_64.c b/arch/x86/kernel/aperture_64.c
index 2c4d5ece7456..58176b56354e 100644
--- a/arch/x86/kernel/aperture_64.c
+++ b/arch/x86/kernel/aperture_64.c
@@ -264,18 +264,23 @@ static int __init parse_gart_mem(char *p)
}
early_param("gart_fix_e820", parse_gart_mem);
+/*
+ * With kexec/kdump, if the first kernel doesn't shut down the GART and the
+ * second kernel allocates a different GART region, there might be two
+ * overlapping GART regions present:
+ *
+ * - the first still used by the GART initialized in the first kernel.
+ * - (sub-)set of it used as normal RAM by the second kernel.
+ *
+ * which leads to memory corruptions and a kernel panic eventually.
+ *
+ * This can also happen if the BIOS has forgotten to mark the GART region
+ * as reserved.
+ *
+ * Try to update the e820 map to mark that new region as reserved.
+ */
void __init early_gart_iommu_check(void)
{
- /*
- * in case it is enabled before, esp for kexec/kdump,
- * previous kernel already enable that. memset called
- * by allocate_aperture/__alloc_bootmem_nopanic cause restart.
- * or second kernel have different position for GART hole. and new
- * kernel could use hole as RAM that is still used by GART set by
- * first kernel
- * or BIOS forget to put that in reserved.
- * try to update e820 to make that region as reserved.
- */
u32 agp_aper_order = 0;
int i, fix, slot, valid_agp = 0;
u32 ctl;
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