[PATCH v2] arm: Fix memory attribute inconsistencies when using fixmap

[Jon Medhurst (Tixy)]

On Tue, 2017-03-21 at 17:30 +0000, Jon Medhurst wrote:
> To cope with the variety in ARM architectures and configurations, the
> pagetable attributes for kernel memory are generated at runtime to match
> the system the kernel finds itself on. This calculated value is stored
> in pgprot_kernel.
> 
> However, when early fixmap support was added for arm (commit
> a5f4c561b3b1) the attributes used for mappings were hard coded because
> pgprot_kernel is not set up early enough. Unfortunately, when fixmap is
> used after early boot this means the memory being mapped can have
> different attributes to existing mappings, potentially leading to
> unpredictable behaviour. A specific problem also exists due to the hard
> coded values not include the 'shareable' attribute which means on
> systems where this matters (e.g. those with multiple CPU clusters) the
> cache contents for a memory location can become inconsistent between
> CPUs.
> 
> To resolve these issues we change fixmap to use the same memory
> attributes (from pgprot_kernel) that the rest of the kernel uses. To
> enable this we need to refactor the initialisation code so
> build_mem_type_table is called early enough. Note, that relies on early
> param parsing for memory type overrides passed via the kernel command
> line, so we need to make sure this call is still after
> parse_early_params().
> 
> Fixes: a5f4c561b3b1 ("ARM: 8415/1: early fixmap support for earlycon")
> Cc: stable at vger.kernel.org # v4.3+

Sorry, this should have...
Signed-off-by: Jon Medhurst <tixy at linaro.org>

> ---
> 
> Changes since v1:
> - Completely rewritten based on Russell's and Ard's sugestions
> - Subject changed from "arm: Fix cache inconsistency when using fixmap"
> 
> 
>  arch/arm/include/asm/fixmap.h |  7 +------
>  arch/arm/include/asm/mmu.h    |  2 ++
>  arch/arm/kernel/setup.c       |  5 +----
>  arch/arm/mm/mmu.c             | 12 ++++++++++--
>  4 files changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
> index 5c17d2dec777..c54f06ace2a1 100644
> --- a/arch/arm/include/asm/fixmap.h
> +++ b/arch/arm/include/asm/fixmap.h
> @@ -41,7 +41,7 @@ static const enum fixed_addresses __end_of_fixed_addresses =
>  
>  #define FIXMAP_PAGE_COMMON	(L_PTE_YOUNG | L_PTE_PRESENT | L_PTE_XN | L_PTE_DIRTY)
>  
> -#define FIXMAP_PAGE_NORMAL	(FIXMAP_PAGE_COMMON | L_PTE_MT_WRITEBACK)
> +#define FIXMAP_PAGE_NORMAL	(pgprot_kernel | L_PTE_XN)
>  #define FIXMAP_PAGE_RO		(FIXMAP_PAGE_NORMAL | L_PTE_RDONLY)
>  
>  /* Used by set_fixmap_(io|nocache), both meant for mapping a device */
> @@ -53,13 +53,8 @@ static const enum fixed_addresses __end_of_fixed_addresses =
>  #ifdef CONFIG_MMU
>  
>  void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot);
> -void __init early_fixmap_init(void);
>  
>  #include <asm-generic/fixmap.h>
>  
> -#else
> -
> -static inline void early_fixmap_init(void) { }
> -
>  #endif
>  #endif
> diff --git a/arch/arm/include/asm/mmu.h b/arch/arm/include/asm/mmu.h
> index a5b47421059d..920d29ca5c3b 100644
> --- a/arch/arm/include/asm/mmu.h
> +++ b/arch/arm/include/asm/mmu.h
> @@ -24,6 +24,8 @@ typedef struct {
>  #define ASID(mm)	(0)
>  #endif
>  
> +void early_mm_init(void);
> +
>  #else
>  
>  /*
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index f4e54503afa9..37c59589aac3 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -40,7 +40,6 @@
>  #include <asm/efi.h>
>  #include <asm/elf.h>
>  #include <asm/early_ioremap.h>
> -#include <asm/fixmap.h>
>  #include <asm/procinfo.h>
>  #include <asm/psci.h>
>  #include <asm/sections.h>
> @@ -1082,12 +1081,10 @@ void __init setup_arch(char **cmdline_p)
>  	strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
>  	*cmdline_p = cmd_line;
>  
> -	early_fixmap_init();
> -	early_ioremap_init();
> -
>  	parse_early_param();
>  
>  #ifdef CONFIG_MMU
> +	early_mm_init();
>  	early_paging_init(mdesc);
>  #endif
>  	setup_dma_zone(mdesc);
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 4e016d7f37b3..f81809e6bd10 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -22,6 +22,7 @@
>  #include <asm/cputype.h>
>  #include <asm/sections.h>
>  #include <asm/cachetype.h>
> +#include <asm/early_ioremap.h>
>  #include <asm/fixmap.h>
>  #include <asm/sections.h>
>  #include <asm/setup.h>
> @@ -382,7 +383,7 @@ static inline pmd_t * __init fixmap_pmd(unsigned long addr)
>  	return pmd;
>  }
>  
> -void __init early_fixmap_init(void)
> +static void __init early_fixmap_init(void)
>  {
>  	pmd_t *pmd;
>  
> @@ -1616,7 +1617,6 @@ void __init paging_init(const struct machine_desc *mdesc)
>  {
>  	void *zero_page;
>  
> -	build_mem_type_table();
>  	prepare_page_table();
>  	map_lowmem();
>  	memblock_set_current_limit(arm_lowmem_limit);
> @@ -1636,3 +1636,11 @@ void __init paging_init(const struct machine_desc *mdesc)
>  	empty_zero_page = virt_to_page(zero_page);
>  	__flush_dcache_page(NULL, empty_zero_page);
>  }
> +
> +void __init early_mm_init(void)
> +{
> +	build_mem_type_table();
> +
> +	early_fixmap_init();
> +	early_ioremap_init();
> +}