linux-kernel - Re: [PATCH v12 05/18] xen/mmu/p2m: Refactor the xen_pagetable

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Message-ID: <alpine.DEB.2.02.1401031544180.8667@kaball.uk.xensource.com>
Date:	Fri, 3 Jan 2014 15:47:15 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	<boris.ostrovsky@...cle.com>, <david.vrabel@...rix.com>,
	<stefano.stabellini@...citrix.com>, <mukesh.rathor@...cle.com>
Subject: Re: [PATCH v12 05/18] xen/mmu/p2m: Refactor the xen_pagetable_init
 code.

On Tue, 31 Dec 2013, Konrad Rzeszutek Wilk wrote:
> The revector and copying of the P2M only happens when
> !auto-xlat and on 64-bit builds. It is not obvious from
> the code, so lets have seperate 32 and 64-bit functions.
> 
> We also invert the check for auto-xlat to make the code
> flow simpler.
> 
> Suggested-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/mmu.c | 73 ++++++++++++++++++++++++++++++------------------------
>  1 file changed, 40 insertions(+), 33 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index ce563be..d792a69 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1198,44 +1198,40 @@ static void __init xen_cleanhighmap(unsigned long vaddr,
>  	 * instead of somewhere later and be confusing. */
>  	xen_mc_flush();
>  }
> -#endif
> -static void __init xen_pagetable_init(void)
> +static void __init xen_pagetable_p2m_copy(void)
>  {
> -#ifdef CONFIG_X86_64
>  	unsigned long size;
>  	unsigned long addr;
> -#endif
> -	paging_init();
> -	xen_setup_shared_info();
> -#ifdef CONFIG_X86_64
> -	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> -		unsigned long new_mfn_list;
> +	unsigned long new_mfn_list;
> +
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		return;
> +
> +	size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> +
> +	/* On 32-bit, we get zero so this never gets executed. */

Given that this code is already ifdef'ed CONFIG_X86_64, this comment
should be removed.


> +	new_mfn_list = xen_revector_p2m_tree();

I take from the comment that new_mfn_list must not be zero. Maybe we
want a BUG_ON or a WARN_ON?


> +	if (new_mfn_list && new_mfn_list != xen_start_info->mfn_list) {
> +		/* using __ka address and sticking INVALID_P2M_ENTRY! */
> +		memset((void *)xen_start_info->mfn_list, 0xff, size);
> +
> +		/* We should be in __ka space. */
> +		BUG_ON(xen_start_info->mfn_list < __START_KERNEL_map);
> +		addr = xen_start_info->mfn_list;
> +		/* We roundup to the PMD, which means that if anybody at this stage is
> +		 * using the __ka address of xen_start_info or xen_start_info->shared_info
> +		 * they are in going to crash. Fortunatly we have already revectored
> +		 * in xen_setup_kernel_pagetable and in xen_setup_shared_info. */
> +		size = roundup(size, PMD_SIZE);
> +		xen_cleanhighmap(addr, addr + size);
>  
>  		size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> +		memblock_free(__pa(xen_start_info->mfn_list), size);
> +		/* And revector! Bye bye old array */
> +		xen_start_info->mfn_list = new_mfn_list;
> +	} else
> +		return;

This was a normal condition when the function was executed on both
x86_64 and x86_32. Now that it is only executed on x86_64, is it still
the case?


> -		/* On 32-bit, we get zero so this never gets executed. */
> -		new_mfn_list = xen_revector_p2m_tree();
> -		if (new_mfn_list && new_mfn_list != xen_start_info->mfn_list) {
> -			/* using __ka address and sticking INVALID_P2M_ENTRY! */
> -			memset((void *)xen_start_info->mfn_list, 0xff, size);
> -
> -			/* We should be in __ka space. */
> -			BUG_ON(xen_start_info->mfn_list < __START_KERNEL_map);
> -			addr = xen_start_info->mfn_list;
> -			/* We roundup to the PMD, which means that if anybody at this stage is
> -			 * using the __ka address of xen_start_info or xen_start_info->shared_info
> -			 * they are in going to crash. Fortunatly we have already revectored
> -			 * in xen_setup_kernel_pagetable and in xen_setup_shared_info. */
> -			size = roundup(size, PMD_SIZE);
> -			xen_cleanhighmap(addr, addr + size);
> -
> -			size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
> -			memblock_free(__pa(xen_start_info->mfn_list), size);
> -			/* And revector! Bye bye old array */
> -			xen_start_info->mfn_list = new_mfn_list;
> -		} else
> -			goto skip;
> -	}
>  	/* 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
> @@ -1255,8 +1251,19 @@ static void __init xen_pagetable_init(void)
>  	 * anything at this stage. */
>  	xen_cleanhighmap(MODULES_VADDR, roundup(MODULES_VADDR, PUD_SIZE) - 1);
>  #endif
> -skip:
> +}
> +#else
> +static void __init xen_pagetable_p2m_copy(void)
> +{
> +	/* Nada! */
> +}
>  #endif
> +
> +static void __init xen_pagetable_init(void)
> +{
> +	paging_init();
> +	xen_setup_shared_info();
> +	xen_pagetable_p2m_copy();
>  	xen_post_allocator_init();
>  }
>  static void xen_write_cr2(unsigned long cr2)
> -- 
> 1.8.3.1
> 
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