From 63ecd3b13d5cf07959a2315ec62a7c62e20df114 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Thu, 1 Nov 2018 16:24:43 +0100 Subject: [PATCH] x86/gart: Rewrite early_gart_iommu_check() comment ... to actually explain what the function is trying to do. Reported-by: Mike Rapoport Signed-off-by: Borislav Petkov Reviewed-by: Thomas Gleixner Cc: 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;