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Date:	Wed, 06 Aug 2014 19:24:20 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
CC:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Rob Herring <robh@...nel.org>, Liu hua <sdu.liu@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Tomasz Figa <t.figa@...sung.com>,
	Will Deacon <will.deacon@....com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Doug Anderson <dianders@...gle.com>,
	Rabin Vincent <rabin@....in>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Mark Salter <msalter@...hat.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/7] arm: use generic fixmap.h

On 8/6/2014 12:32 PM, Kees Cook wrote:
> From: Mark Salter <msalter@...hat.com>
> 
> ARM is different from other architectures in that fixmap pages are indexed
> with a positive offset from FIXADDR_START.  Other architectures index with
> a negative offset from FIXADDR_TOP.  In order to use the generic fixmap.h
> definitions, this patch redefines FIXADDR_TOP to be inclusive of the
> useable range.  That is, FIXADDR_TOP is the virtual address of the topmost
> fixed page.  The newly defined FIXADDR_END is the first virtual address
> past the fixed mappings.
> 
> Signed-off-by: Mark Salter <msalter@...hat.com>
> Reviewed-by: Doug Anderson <dianders@...omium.org>
> [update for "ARM: 8031/2: change fixmap mapping region to support 32 CPUs"]
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  arch/arm/include/asm/fixmap.h | 27 +++++++++------------------
>  arch/arm/mm/init.c            |  2 +-
>  2 files changed, 10 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
> index 74124b0d0d79..190142d174ee 100644
> --- a/arch/arm/include/asm/fixmap.h
> +++ b/arch/arm/include/asm/fixmap.h
> @@ -2,27 +2,18 @@
>  #define _ASM_FIXMAP_H
>  
>  #define FIXADDR_START		0xffc00000UL
> -#define FIXADDR_TOP		0xffe00000UL
> -#define FIXADDR_SIZE		(FIXADDR_TOP - FIXADDR_START)
> +#define FIXADDR_END		0xffe00000UL
> +#define FIXADDR_TOP		(FIXADDR_END - PAGE_SIZE)
> +#define FIXADDR_SIZE		(FIXADDR_END - FIXADDR_START)
>  
>  #define FIX_KMAP_NR_PTES	(FIXADDR_SIZE >> PAGE_SHIFT)
>  
> -#define __fix_to_virt(x)	(FIXADDR_START + ((x) << PAGE_SHIFT))
> -#define __virt_to_fix(x)	(((x) - FIXADDR_START) >> PAGE_SHIFT)
> +enum fixed_addresses {
> +	FIX_KMAP_BEGIN,
> +	FIX_KMAP_END = FIX_KMAP_NR_PTES - 1,
> +	__end_of_fixed_addresses
> +};
>  
> -extern void __this_fixmap_does_not_exist(void);
> -
> -static inline unsigned long fix_to_virt(const unsigned int idx)
> -{
> -	if (idx >= FIX_KMAP_NR_PTES)
> -		__this_fixmap_does_not_exist();
> -	return __fix_to_virt(idx);
> -}
> -
> -static inline unsigned int virt_to_fix(const unsigned long vaddr)
> -{
> -	BUG_ON(vaddr >= FIXADDR_TOP || vaddr < FIXADDR_START);
> -	return __virt_to_fix(vaddr);
> -}
> +#include <asm-generic/fixmap.h>
>  
>  #endif
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 659c75d808dc..ad82c05bfc3a 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -570,7 +570,7 @@ void __init mem_init(void)
>  			MLK(DTCM_OFFSET, (unsigned long) dtcm_end),
>  			MLK(ITCM_OFFSET, (unsigned long) itcm_end),
>  #endif
> -			MLK(FIXADDR_START, FIXADDR_TOP),
> +			MLK(FIXADDR_START, FIXADDR_END),
>  			MLM(VMALLOC_START, VMALLOC_END),
>  			MLM(PAGE_OFFSET, (unsigned long)high_memory),
>  #ifdef CONFIG_HIGHMEM
> 

I'm working off of a 3.14 kernel and with this backported 
kmap_atomic does not actually map properly for me. This was

my quick fix (not sure if we should be using __set_fixmap?). Or did
I fail at backportery?

-----8<-----
>From ea11b54704aa0a311ab3d05fd70072679bfe1a0b Mon Sep 17 00:00:00 2001
From: Laura Abbott <lauraa@...eaurora.org>
Date: Wed, 6 Aug 2014 19:20:46 -0700
Subject: [PATCH] arm: Get proper pte for fixmaps

The generic fixmap.h gets indexes from high to low instead
of low to high so the fixmap idx does not correspond to
the array entry in fixmap_page_table. Get the proper pte
to update.

Signed-off-by: Laura Abbott <lauraa@...eaurora.org>
---
 arch/arm/mm/highmem.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index bedca3a..7f08e64 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -22,14 +22,18 @@
 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 *ppte = pte_offset_kernel(pmd_off_k(FIXADDR_START), vaddr);
+
+	set_pte_ext(ppte, pte, 0);
 	local_flush_tlb_kernel_page(vaddr);
 }
 
 static inline pte_t get_fixmap_pte(unsigned long vaddr)
 {
 	unsigned long idx = __virt_to_fix(vaddr);
-	return *(fixmap_page_table + idx);
+	pte_t *ppte = pte_offset_kernel(pmd_off_k(FIXADDR_START), vaddr);
+
+	return *ppte;
 }
 
 void *kmap(struct page *page)
-- 
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