[PATCH v4 10/13] arm64: move kernel mapping out of linear region

[Catalin Marinas]

On Wed, Apr 15, 2015 at 05:34:21PM +0200, Ard Biesheuvel wrote:
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index f800d45ea226..801331793bd3 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -24,6 +24,7 @@
>  #include <linux/compiler.h>
>  #include <linux/const.h>
>  #include <linux/types.h>
> +#include <asm/boot.h>
>  #include <asm/sizes.h>
>  
>  /*
> @@ -39,7 +40,12 @@
>  #define PCI_IO_SIZE		SZ_16M
>  
>  /*
> - * PAGE_OFFSET - the virtual address of the start of the kernel image (top
> + * Offset below PAGE_OFFSET where to map the kernel Image.
> + */
> +#define KIMAGE_OFFSET		MAX_KIMG_SIZE
> +
> +/*
> + * PAGE_OFFSET - the virtual address of the base of the linear mapping (top
>   *		 (VA_BITS - 1))
>   * VA_BITS - the maximum number of bits for virtual addresses.
>   * TASK_SIZE - the maximum size of a user space task.
> @@ -49,7 +55,8 @@
>   */
>  #define VA_BITS			(CONFIG_ARM64_VA_BITS)
>  #define PAGE_OFFSET		(UL(0xffffffffffffffff) << (VA_BITS - 1))
> -#define MODULES_END		(PAGE_OFFSET)
> +#define KIMAGE_VADDR		(PAGE_OFFSET - KIMAGE_OFFSET)
> +#define MODULES_END		KIMAGE_VADDR
>  #define MODULES_VADDR		(MODULES_END - SZ_64M)
>  #define PCI_IO_END		(MODULES_VADDR - SZ_2M)
>  #define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)
> @@ -77,7 +84,11 @@
>   * private definitions which should NOT be used outside memory.h
>   * files.  Use virt_to_phys/phys_to_virt/__pa/__va instead.
>   */
> -#define __virt_to_phys(x)	(((phys_addr_t)(x) - PAGE_OFFSET + PHYS_OFFSET))
> +#define __virt_to_phys(x) ({						\
> +	long __x = (long)(x) - PAGE_OFFSET;				\
> +	__x >= 0 ? (phys_addr_t)(__x + PHYS_OFFSET) : 			\
> +		   (phys_addr_t)(__x + PHYS_OFFSET + kernel_va_offset); })

Just wondering, when do we need a __pa on kernel addresses? But it looks
to me like second case is always (__x + PHYS_OFFSET + KIMAGE_OFFSET).
Before map_mem(), we have phys_offset_bias set but kernel_va_offset 0.
After map_mem(), we reset the former and set the latter. Maybe we can
get rid of kernel_va_offset entirely (see more below about
phys_offset_bias).

> +
>  #define __phys_to_virt(x)	((unsigned long)((x) - PHYS_OFFSET + PAGE_OFFSET))
>  
>  /*
> @@ -111,7 +122,16 @@
>  
>  extern phys_addr_t		memstart_addr;
>  /* PHYS_OFFSET - the physical address of the start of memory. */
> -#define PHYS_OFFSET		({ memstart_addr; })
> +#define PHYS_OFFSET		({ memstart_addr + phys_offset_bias; })
> +
> +/*
> + * Before the linear mapping has been set up, __va() translations will
> + * not produce usable virtual addresses unless we tweak PHYS_OFFSET to
> + * compensate for the offset between the kernel mapping and the base of
> + * the linear mapping. We will undo this in map_mem().
> + */
> +extern u64 phys_offset_bias;
> +extern u64 kernel_va_offset;

Can we not add the bias to memstart_addr during boot and reset it later
in map_mem()? Otherwise the run-time kernel ends up having to do a dummy
addition any time it needs PHYS_OFFSET.

-- 
Catalin