linux-kernel - Re: [PATCH v7u1 01/31] x86, mm: Fix page table early allocation offset checking

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Date:	Tue, 15 Jan 2013 12:27:27 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, Jan Kiszka <jan.kiszka@....de>,
	Jason Wessel <jason.wessel@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7u1 01/31] x86, mm: Fix page table early allocation
 offset checking

On Fri, 4 Jan 2013, Yinghai Lu wrote:
> During debugging loading kernel above 4G, found one page if is not used
> in BRK with early page allocation.
> 
> pgt_buf_top is address that can not be used, so should check if that new
> end is above that top, otherwise last page will not be used.
> 
> Fix that checking and also add print out for every allocation from BRK.
> 
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>

Acked-by: Stefano Stabellini <stefano.stabellini@...citrix.com>


>  arch/x86/mm/init.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 6f85de8..c4293cf 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -47,7 +47,7 @@ __ref void *alloc_low_pages(unsigned int num)
>  						__GFP_ZERO, order);
>  	}
>  
> -	if ((pgt_buf_end + num) >= pgt_buf_top) {
> +	if ((pgt_buf_end + num) > pgt_buf_top) {
>  		unsigned long ret;
>  		if (min_pfn_mapped >= max_pfn_mapped)
>  			panic("alloc_low_page: ran out of memory");
> @@ -61,6 +61,8 @@ __ref void *alloc_low_pages(unsigned int num)
>  	} else {
>  		pfn = pgt_buf_end;
>  		pgt_buf_end += num;
> +		printk(KERN_DEBUG "BRK [%#010lx, %#010lx] PGTABLE\n",
> +			pfn << PAGE_SHIFT, (pgt_buf_end << PAGE_SHIFT) - 1);
>  	}
>  
>  	for (i = 0; i < num; i++) {
> -- 
> 1.7.10.4
> 
> --
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