linux-kernel - Re: [Xen-devel] [PATCH] xen: switch to post-init routines in xen mmu.c earlier

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Date:	Wed, 10 Dec 2014 18:07:02 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<david.vrabel@...rix.com>, <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH] xen: switch to post-init routines in xen
 mmu.c earlier

On 10/12/14 15:56, Juergen Gross wrote:
> With the virtual mapped linear p2m list the post-init mmu operations
> must be used for setting up the p2m mappings, as in case of
> CONFIG_FLATMEM the init routines may trigger BUGs.
> 
> Reported-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/x86/xen/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 6ab6150..a1a429a 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1225,6 +1225,7 @@ static void __init xen_pagetable_p2m_setup(void)
>  static void __init xen_pagetable_init(void)
>  {
>  	paging_init();
> +	xen_post_allocator_init();
>  
>  	xen_pagetable_p2m_setup();
>  

This feels very chicken-and-egg to me:  To setup the P2M we need to use
the MMU ops that use the P2M...

Please explain very clearly why this is all safe.

> @@ -1236,7 +1237,6 @@ static void __init xen_pagetable_init(void)
>  		xen_remap_memory();
>  
>  	xen_setup_shared_info();
> -	xen_post_allocator_init();
>  }
>  static void xen_write_cr2(unsigned long cr2)
>  {
> 

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