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x86/gart: Rewrite early_gart_iommu_check() comment 

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

Reported-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <x86@kernel.org>
Link: http://lkml.kernel.org/r/20181101155314.30690-1-bp@alien8.de
This commit is contained in:
Borislav Petkov 2018-11-01 16:24:43 +01:00
parent 651022382c
commit 63ecd3b13d
1 changed files with 15 additions and 10 deletions
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25
arch/x86/kernel/aperture_64.c
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@ -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;