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

[Brian Gerst]

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.

--
Brian Gerst