linux-kernel - Re: [PATCH v3 2/2] ARM : change fixmap mapping region to support 32 CPUs

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Date:	Wed, 6 Aug 2014 13:21:18 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Kees Cook <keescook@...omium.org>
cc:	Liu hua <sdu.liu@...wei.com>, Rob Herring <robherring2@...il.com>,
	wangnan0 <wangnan0@...wei.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	peifeiyue <peifeiyue@...wei.com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vitaly Andrianov <vitalya@...com>,
	Rabin Vincent <rabin@....in>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	"liusdu@....com" <liusdu@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Salter <msalter@...hat.com>
Subject: Re: [PATCH v3 2/2] ARM : change fixmap mapping region to support 32
 CPUs

On Wed, 6 Aug 2014, Kees Cook wrote:

> With the original code, there is (I think) a page table entry for the
> fixmap range. For the latter, there isn't. I see a NULL pgd entry
> fault when trying to use it, and noticed that this only exists under
> highmem:
> 
> static void __init kmap_init(void)
> {
> #ifdef CONFIG_HIGHMEM
>         pkmap_page_table = early_pte_alloc(pmd_off_k(PKMAP_BASE),
>                 PKMAP_BASE, _PAGE_KERNEL_TABLE);
> 
>         fixmap_page_table = early_pte_alloc(pmd_off_k(FIXADDR_START),
>                 FIXADDR_START, _PAGE_KERNEL_TABLE);
> #endif
> }

The above is wrong.  The fixmap PTEs must be allocated unconditionally 
irrespective of highmem.  So the #endif should be moved up by 3 lines.


Nicolas
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