[PATCH v3 4/4] arm64: prevent __va() translations before memstart_addr is assigned

[Catalin Marinas]

On Mon, Feb 22, 2016 at 04:52:09PM +0000, Will Deacon wrote:
> On Fri, Feb 12, 2016 at 03:57:26PM +0100, Ard Biesheuvel wrote:
> > Since memstart_addr is assigned relatively late in the boot code,
> > after generic code like DT parsing and memblock manipulation has
> > already occurred, we need to ensure that no __va() translation occur
> > until memstart_addr has been set to a meaningful value.
> > 
> > So initialize memstart_addr to a value that cannot represent a valid
> > physical address, and BUG() if memstart_addr is referenced while it
> > still holds this value. Note that the > comparison against LLONG_MAX
> > (not ULLONG_MAX) resolves to a single tbnz instruction that performs
> > a conditional jump to a brk instruction that is emitted out of line.
> 
> Even so, I'd imagine that having a measurable impact on system
> performance. Did you have a go at benchmarking this?

Good point, I forgot about this discussion. We should revert this part
indeed or at least make it dependent on some config option like
DEBUG_VM.

-- 
Catalin