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

[Catalin Marinas]

On Thu, Aug 20, 2015 at 01:54:40PM +0200, Ard Biesheuvel wrote:
> 
> 
> > 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

Just leave it as it is, not sure it's any clearer. Basically the maximum
size we can map is (0 - PAGE_OFFSET), so if we make the range inclusive,
we get to memstart_addr - PAGE_OFFSET - 1.

-- 
Catalin