linux-kernel - Re: [PATCH 2/4] xen/x86: Use memblock

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Date:	Fri, 27 Jul 2012 11:49:02 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH 2/4] xen/x86: Use memblock_reserve for sensitive areas.

On Thu, 26 Jul 2012, Konrad Rzeszutek Wilk wrote:
> instead of a big memblock_reserve. This way we can be more
> selective in freeing regions (and it also makes it easier
> to understand where is what).
> 
> [v1: Move the auto_translate_physmap to proper line]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/enlighten.c |   38 ++++++++++++++++++++++++++++++++++++++
>  arch/x86/xen/p2m.c       |    5 +++++
>  arch/x86/xen/setup.c     |    9 ---------
>  3 files changed, 43 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index ff962d4..9b1afa4 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -998,7 +998,44 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
>  
>  	return ret;
>  }
> +static void __init xen_reserve_mfn(unsigned long mfn)
> +{
> +	unsigned long pfn;
> +
> +	if (!mfn)
> +		return;
> +	pfn = mfn_to_pfn(mfn);
> +	if (phys_to_machine_mapping_valid(pfn))
> +		memblock_reserve(PFN_PHYS(pfn), PAGE_SIZE);
> +}

If the mfn is not in the m2p xen_reserve_mfn won't do anything. It is
worth writing it down in a comment.


> +static void __init xen_reserve_internals(void)
> +{
> +	unsigned long size;
> +
> +	if (!xen_pv_domain())
> +		return;
> +
> +	memblock_reserve(__pa(xen_start_info), PAGE_SIZE);

xen_start_info is not in the m2p, so you cannot use xen_reserve_mfn


> +	xen_reserve_mfn(PFN_DOWN(xen_start_info->shared_info));
> +	xen_reserve_mfn(xen_start_info->store_mfn);

Are we sure that shared_info points to an mfn that is in the m2p (rather
than a special mfn not present in the list)?


> +	if (!xen_initial_domain())
> +		xen_reserve_mfn(xen_start_info->console.domU.mfn);
> +
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		return;
> +
> +	/*
> +	 * ALIGN up to compensate for the p2m_page pointing to an array that
> +	 * can partially filled (look in xen_build_dynamic_phys_to_machine).
> +	 */
> +
> +	size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> +	memblock_reserve(__pa(xen_start_info->mfn_list), size);

I take that here you are using memblock_reserve again, rather than
xen_reserve_mfn, because the corresponding mfn is not in the m2p?


> +	/* The pagetables are reserved in mmu.c */
> +}
>  void xen_setup_shared_info(void)
>  {
>  	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> @@ -1362,6 +1399,7 @@ asmlinkage void __init xen_start_kernel(void)
>  	xen_raw_console_write("mapping kernel into physical memory\n");
>  	pgd = xen_setup_kernel_pagetable(pgd, xen_start_info->nr_pages);
>  
> +	xen_reserve_internals();
>  	/* Allocate and initialize top and mid mfn levels for p2m structure */
>  	xen_build_mfn_list_list();
>  
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index e4adbfb..6a2bfa4 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -388,6 +388,11 @@ void __init xen_build_dynamic_phys_to_machine(void)
>  	}
>  
>  	m2p_override_init();
> +
> +	/* NOTE: We cannot call memblock_reserve here for the mfn_list as there
> +	 * isn't enough pieces to make it work (for one - we are still using the
> +	 * Xen provided pagetable). Do it later in xen_reserve_internals.
> +	 */
>  }
>  
>  unsigned long get_phys_to_machine(unsigned long pfn)
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index a4790bf..9efca75 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -424,15 +424,6 @@ char * __init xen_memory_setup(void)
>  	e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
>  			E820_RESERVED);
>  
> -	/*
> -	 * Reserve Xen bits:
> -	 *  - mfn_list
> -	 *  - xen_start_info
> -	 * See comment above "struct start_info" in <xen/interface/xen.h>
> -	 */
> -	memblock_reserve(__pa(xen_start_info->mfn_list),
> -			 xen_start_info->pt_base - xen_start_info->mfn_list);
> -
>  	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
>  
>  	return "Xen";
> -- 
> 1.7.7.6
> 
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