linux-kernel - Re: [ 18/85] x86: Exclude E820_RESERVED regions and memory holes above 4 GB from direct mapping.

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Date:	Sat, 27 Oct 2012 17:27:55 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Jacob Shin <jacob.shin@....com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	alan@...rguk.ukuu.org.uk,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [ 18/85] x86: Exclude E820_RESERVED regions and memory holes
 above 4 GB from direct mapping.

On Thu, 2012-10-25 at 17:05 -0700, Greg Kroah-Hartman wrote:
> 3.6-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Jacob Shin <jacob.shin@....com>
> 
> commit 1bbbbe779aabe1f0768c2bf8f8c0a5583679b54a upstream.
> 
> On systems with very large memory (1 TB in our case), BIOS may report a
> reserved region or a hole in the E820 map, even above the 4 GB range. Exclude
> these from the direct mapping.
> 
> [ hpa: this should be done not just for > 4 GB but for everything above the legacy
>   region (1 MB), at the very least.  That, however, turns out to require significant
>   restructuring.  That work is well underway, but is not suitable for rc/stable. ]
[...]
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -919,8 +919,21 @@ void __init setup_arch(char **cmdline_p)
>  
>  #ifdef CONFIG_X86_64
>  	if (max_pfn > max_low_pfn) {
> -		max_pfn_mapped = init_memory_mapping(1UL<<32,
> -						     max_pfn<<PAGE_SHIFT);
> +		int i;
> +		for (i = 0; i < e820.nr_map; i++) {
> +			struct e820entry *ei = &e820.map[i];
> +
> +			if (ei->addr + ei->size <= 1UL << 32)
> +				continue;
> +
> +			if (ei->type == E820_RESERVED)
> +				continue;
> +
> +			max_pfn_mapped = init_memory_mapping(
> +				ei->addr < 1UL << 32 ? 1UL << 32 : ei->addr,
> +				ei->addr + ei->size);

Is it safe to assume that the e820 entries are sorted?  If not, this
assignment needs to be conditional.

Ben.

> +		}
> +
>  		/* can we preseve max_low_pfn ?*/
>  		max_low_pfn = max_pfn;
>  	}

-- 
Ben Hutchings
Never attribute to conspiracy what can adequately be explained by stupidity.

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