linux-kernel - Re: [PATCH v4 2/8] ARM: expand fixmap region to 3MB

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Date:	Wed, 20 Aug 2014 07:16:34 -0500
From:	Kees Cook <keescook@...omium.org>
To:	Will Deacon <will.deacon@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh@...nel.org>,
	Laura Abbott <lauraa@...eaurora.org>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"msalter@...hat.com" <msalter@...hat.com>,
	Rabin Vincent <rabin@....in>, Liu hua <sdu.liu@...wei.com>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Doug Anderson <dianders@...gle.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 2/8] ARM: expand fixmap region to 3MB

On Tue, Aug 19, 2014 at 7:26 AM, Will Deacon <will.deacon@....com> wrote:
> Hi Kees, Rob,
>
> On Wed, Aug 13, 2014 at 06:06:27PM +0100, Kees Cook wrote:
>> From: Rob Herring <robh@...nel.org>
>>
>> With commit a05e54c103b0 ("ARM: 8031/2: change fixmap mapping region to
>> support 32 CPUs"), the fixmap region was expanded to 2MB, but it
>> precluded any other uses of the fixmap region. In order to support other
>> uses the fixmap region needs to be expanded beyond 2MB. Fortunately, the
>> adjacent 1MB range 0xffe00000-0xfff00000 is availabe.
>>
>> Remove fixmap_page_table ptr and lookup the page table via the virtual
>> address so that the fixmap region can span more that one pmd. The 2nd
>> pmd is already created since it is shared with the vector page.
>
> [...]
>
>> diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
>> index 45aeaaca9052..81061987ac45 100644
>> --- a/arch/arm/mm/highmem.c
>> +++ b/arch/arm/mm/highmem.c
>> @@ -18,19 +18,20 @@
>>  #include <asm/tlbflush.h>
>>  #include "mm.h"
>>
>> -pte_t *fixmap_page_table;
>> -
>>  static inline void set_fixmap_pte(int idx, pte_t pte)
>>  {
>>       unsigned long vaddr = __fix_to_virt(idx);
>> -     set_pte_ext(fixmap_page_table + idx, pte, 0);
>> +     pte_t *ptep = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
>> +
>> +     set_pte_ext(ptep, pte, 0);
>>       local_flush_tlb_kernel_page(vaddr);
>>  }
>
> Minor comment, but we can drop the ifx parameter here now, right? It looks a
> bit weird having a setter/getter pair of functions where the type signatures
> aren't the inverse.

idx is used to get the vaddr here. I suppose the various users of
these functions in highmem could be reworked, but that doesn't look
sensible either. Maybe it's just the names of the functions that are
confusing?

-Kees

-- 
Kees Cook
Chrome OS Security
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