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Commit 63ecd3b1 authored by Borislav Petkov's avatar Borislav Petkov
Browse files

x86/gart: Rewrite early_gart_iommu_check() comment 



... to actually explain what the function is trying to do.

Reported-by: default avatarMike Rapoport <rppt@linux.ibm.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: <x86@kernel.org>
Link: http://lkml.kernel.org/r/20181101155314.30690-1-bp@alien8.de
parent 65102238

arch/x86/kernel/aperture_64.c

+15 −10
Original line number Diff line number Diff line
@@ -264,18 +264,23 @@ static int __init parse_gart_mem(char *p) 
}

early_param("gart_fix_e820", parse_gart_mem);



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.

 * 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)

{

	u32 agp_aper_order = 0;

	int i, fix, slot, valid_agp = 0;

	u32 ctl;