Re: [Xen-devel] [PATCH 7/7] xen/mmu: Remove from __ka space PMD entries for pagetables.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 26 Jul 2012, Konrad Rzeszutek Wilk wrote:
> Please first read the description in "xen/mmu: Copy and revector the
> P2M tree."
> 
> At this stage, the __ka address space (which is what the old
> P2M tree was using) is partially disassembled. The cleanup_highmap
> has removed the PMD entries from 0-16MB and anything past _brk_end
> up to the max_pfn_mapped (which is the end of the ramdisk).
> 
> The xen_remove_p2m_tree and code around has ripped out the __ka for
> the old P2M array.
> 
> Here we continue on doing it to where the Xen page-tables were.
> It is safe to do it, as the page-tables are addressed using __va.
> For good measure we delete anything that is within MODULES_VADDR
> and up to the end of the PMD.
> 
> At this point the __ka only contains PMD entries for the start
> of the kernel up to __brk.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  arch/x86/xen/mmu.c |   20 ++++++++++++++++++++
>  1 files changed, 20 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 05e8492..738feca 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1241,6 +1241,26 @@ static void __init xen_pagetable_setup_done(pgd_t 
> *base)
>                       xen_start_info->mfn_list = new_mfn_list;
>               }
>       }
> +#ifdef CONFIG_X86_64
> +     /* At this stage, cleanup_highmap has already cleaned __ka space
> +      * from _brk_limit way up to the max_pfn_mapped (which is the end of
> +      * the ramdisk). We continue on, erasing PMD entries that point to page
> +      * tables - do note that they are accessible at this stage via __va.
> +      * For good measure we also round up to the PMD - which means that if
> +      * anybody is using __ka address to the initial boot-stack - and try
> +      * to use it - they are going to crash. The xen_start_info has been
> +      * taken care of already in xen_setup_kernel_pagetable. */
> +     addr = xen_start_info->pt_base;
> +     size = roundup(xen_start_info->nr_pt_frames * PAGE_SIZE, PMD_SIZE);
> +
> +     xen_cleanhighmap(addr, addr + size);
> +     xen_start_info->pt_base = (unsigned 
> long)__va(__pa(xen_start_info->pt_base));
> +
> +     /* This is superflous and shouldn't be neccessary, but you know what
> +      * lets do it. The MODULES_VADDR -> MODULES_END should be clear of
> +      * anything at this stage. */
> +     xen_cleanhighmap(MODULES_VADDR, roundup(MODULES_VADDR, PUD_SIZE) - 1);

I would stick an #ifdef CONFIG_DEBUG of some kind around it


> +#endif
>       xen_post_allocator_init();
>  }
>  
> -- 
> 1.7.7.6
> 
> 
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> 

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