linux-kernel - Re: [PATCH] x86/mm/init: respect memblock reserved regions when destroying mappings

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Message-ID: <20110214162602.GB11290@dumpdata.com>
Date:	Mon, 14 Feb 2011 11:26:02 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Jan Beulich <JBeulich@...ell.com>
Subject: Re: [PATCH] x86/mm/init: respect memblock reserved regions when
 destroying mappings

> 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@...ell.com>
> 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@...ell.com>
>     Signed-off-by: H. Peter Anvin <hpa@...or.com>
> 
> 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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