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From:   Brian Gerst <brgerst@gmail.com>
Date:   Mon, 27 Nov 2017 07:31:37 -0500
Message-ID: <CAMzpN2joDWU41SpNTu30pnOsZbdNcDMiCZ99HBy53SFVwvxMuw@mail.gmail.com>
Subject: Re: [patch V2 1/5] x86/kaiser: Respect disabled CPU features
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>,
        Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
        Hugh Dickins <hughd@google.com>,
        Kees Cook <keescook@google.com>, Linux-MM <linux-mm@kvack.org>,
        michael.schwarz@iaik.tugraz.at, moritz.lipp@iaik.tugraz.at,
        richard.fellner@student.tugraz.at
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On Mon, Nov 27, 2017 at 6:47 AM, Thomas Gleixner <tglx@linutronix.de> 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

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