Re: [patch V2 1/5] x86/kaiser: Respect disabled CPU features

[Thomas Gleixner]

On Mon, 27 Nov 2017, Brian Gerst wrote:
> On Mon, Nov 27, 2017 at 6:47 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> > On Mon, 27 Nov 2017, Peter Zijlstra wrote:
> >> On Mon, Nov 27, 2017 at 12:14:04AM +0100, Thomas Gleixner wrote:
> >> > PAGE_NX and PAGE_GLOBAL might be not supported or disabled on the command
> >> > line, but KAISER sets them unconditionally.
> >>
> >> So KAISER is x86_64 only, right? AFAIK there is no x86_64 without NX
> >> support. So would it not make sense to mandate NX for KAISER?, that is
> >> instead of making "noexec" + KAISER work, make "noexec" kill KAISER +
> >> emit a warning.
> >
> > OTOH, disabling NX is a simple way to verify that DEBUG_WX works correctly
> > also on the shadow maps.
> >
> > But surely we can drop the PAGE_GLOBAL thing, as all 64bit systems have it.
> 
> I seem to recall that some virtualized environments (maybe Xen?) don't
> support global pages.

Uuurg. Ok, we leave it as is for now. Better safe than sorry. It does no
harm.

Thanks,

	tglx