Re: [PATCH 11/16] x86: add a boot option to enable and disable the direct map

[Wei Liu <wl@xxxxxxx>]

On Fri, May 01, 2020 at 01:59:24PM +0100, Hongyan Xia wrote:
> On Fri, 2020-05-01 at 12:11 +0000, Wei Liu wrote:
> > On Thu, Apr 30, 2020 at 09:44:20PM +0100, Hongyan Xia wrote:
> > > From: Hongyan Xia <hongyxia@xxxxxxxxxx>
> > > 
> > > Also add a helper function to retrieve it. Change
> > > arch_mfn_in_direct_map
> > > to check this option before returning.
> > > 
> > > This is added as a boot command line option, not a Kconfig. We do
> > > not
> > > produce different builds for EC2 so this is not introduced as a
> > > compile-time configuration.
> > 
> > Having a Kconfig will probably allow the compiler to eliminate dead
> > code.
> > 
> > This is not asking you to do the work, someone can come along and
> > adjust 
> > arch_has_directmap easily.
> 
> My original code added this as a CONFIG option, but I converted it into
> a boot-time switch, so I can just dig out history and convert it back.
> I wonder if we should get more opinions on this to make a decision.

Form my perspective, you as a contributor has done the work to scratch
your own itch, hence I said "not asking you to do the work". I don't
want to turn every comment into a formal ask and eventually lead to
feature creep.

> 
> I would love Xen to have static key support though so that a boot-time
> switch costs no run-time performance.
> 

Yes that would be great.

Wei.

> Hongyan
>