Re: [PATCH] x86/mm/init: respect memblock reserved regions whendestroying mappings

From: Konrad Rzeszutek Wilk
Date: Mon Feb 14 2011 - 11:27:27 EST


> BTW: Do we really need to cleanup initial mapping between _brk_end to _end?

Did you try to revert the patch and run it under your setup?
>
> origin patch from jan:
>
> commit 498343967613183611ac37dccb2846496d954c06
> Author: Jan Beulich <jbeulich@xxxxxxxxxx>
> Date: Wed May 6 13:06:47 2009 +0100
>
> x86-64: finish cleanup_highmaps()'s job wrt. _brk_end
>
> With the introduction of the .brk section, special care must be taken
> that no unused page table entries remain if _brk_end and _end are
> separated by a 2M page boundary. cleanup_highmap() runs very early and
> hence cannot take care of that, hence potential entries needing to be
> removed past _brk_end must be cleared once the brk allocator has done
> its job.
>
> [ Impact: avoids undesirable TLB aliases ]
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
> Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
>
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index fd3da1d..ae4f7b5 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -7,6 +7,7 @@
> #include <asm/page.h>
> #include <asm/page_types.h>
> #include <asm/sections.h>
> +#include <asm/setup.h>
> #include <asm/system.h>
> #include <asm/tlbflush.h>
>
> @@ -304,8 +305,23 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
> #endif
>
> #ifdef CONFIG_X86_64
> - if (!after_bootmem)
> + if (!after_bootmem && !start) {
> + pud_t *pud;
> + pmd_t *pmd;
> +
> mmu_cr4_features = read_cr4();
> +
> + /*
> + * _brk_end cannot change anymore, but it and _end may be
> + * located on different 2M pages. cleanup_highmap(), however,
> + * can only consider _end when it runs, so destroy any
> + * mappings beyond _brk_end here.
> + */
> + pud = pud_offset(pgd_offset_k(_brk_end), _brk_end);
> + pmd = pmd_offset(pud, _brk_end - 1);
> + while (++pmd <= pmd_offset(pud, (unsigned long)_end - 1))
> + pmd_clear(pmd);
> + }
> #endif
> __flush_tlb_all();
>
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