[PATCH 2/2] arm64: set MAX_MEMBLOCK_ADDR according to linear region size

[Ard Biesheuvel]

> On 20 aug. 2015, at 11:19, Catalin Marinas <catalin.marinas at arm.com> wrote:
> 
>> On Tue, Aug 18, 2015 at 11:34:42AM +0200, Ard Biesheuvel wrote:
>> The linear region size of a 39-bit VA kernel is only 256 GB, which
>> may be insufficient to cover all of system RAM, even on platforms
>> that have much less than 256 GB of memory but which is laid out
>> very sparsely.
>> 
>> So make sure we clip the memory we will not be able to map before
>> installing it into the memblock memory table, by setting
>> MAX_MEMBLOCK_ADDR accordingly.
>> 
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>> arch/arm64/include/asm/memory.h | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>> 
>> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
>> index f800d45ea226..44a59c20e773 100644
>> --- a/arch/arm64/include/asm/memory.h
>> +++ b/arch/arm64/include/asm/memory.h
>> @@ -114,6 +114,14 @@ extern phys_addr_t        memstart_addr;
>> #define PHYS_OFFSET        ({ memstart_addr; })
>> 
>> /*
>> + * The maximum physical address that the linear direct mapping
>> + * of system RAM can cover. (PAGE_OFFSET can be interpreted as
>> + * a 2's complement signed quantity and negated to derive the
>> + * maximum size of the linear mapping.)
>> + */
>> +#define MAX_MEMBLOCK_ADDR    ({ memstart_addr - PAGE_OFFSET - 1; })
> 
> Would it be easier to understand as just memstart_addr + ~PAGE_OFFSET?
> 

Whichever you prefer

> Otherwise:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>

Thanks