Re: [PATCH V4 2/6] arm64: mm: Introduce DEFAULT_MAP_WINDOW

[Steve Capper <Steve.Capper@arm.com>]

On Wed, Dec 05, 2018 at 05:36:52PM +0000, Catalin Marinas wrote:
> On Wed, Dec 05, 2018 at 04:41:41PM +0000, Steve Capper wrote:
> > We wish to introduce a 52-bit virtual address space for userspace but
> > maintain compatibility with software that assumes the maximum VA space
> > size is 48 bit.
> > 
> > In order to achieve this, on 52-bit VA systems, we make mmap behave as
> > if it were running on a 48-bit VA system (unless userspace explicitly
> > requests a VA where addr[51:48] != 0).
> > 
> > On a system running a 52-bit userspace we need TASK_SIZE to represent
> > the 52-bit limit as it is used in various places to distinguish between
> > kernelspace and userspace addresses.
> > 
> > Thus we need a new limit for mmap, stack, ELF loader and EFI (which uses
> > TTBR0) to represent the non-extended VA space.
> > 
> > This patch introduces DEFAULT_MAP_WINDOW and DEFAULT_MAP_WINDOW_64 and
> > switches the appropriate logic to use that instead of TASK_SIZE.
> > 
> > Signed-off-by: Steve Capper <steve.capper@arm.com>
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Thanks!