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Subject: Re: [patch V2 5/5] x86/kaiser: Add boottime disable switch
To: Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
References: <20171126231403.657575796@linutronix.de>
 <20171126232414.645128754@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com,
        linux-mm@kvack.org, michael.schwarz@iaik.tugraz.at,
        moritz.lipp@iaik.tugraz.at, richard.fellner@student.tugraz.at
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <24359653-5b93-7146-8f65-ac38c3af0069@linux.intel.com>
Date: Mon, 27 Nov 2017 10:22:52 -0800
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On 11/26/2017 03:14 PM, Thomas Gleixner wrote:
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -56,7 +56,7 @@ config SECURITY_NETWORK
>  
>  config KAISER
>  	bool "Remove the kernel mapping in user mode"
> -	depends on X86_64 && SMP && !PARAVIRT
> +	depends on X86_64 && SMP && !PARAVIRT && JUMP_LABEL
>  	help
>  	  This feature reduces the number of hardware side channels by
>  	  ensuring that the majority of kernel addresses are not mapped

One of the reasons for doing the runtime-disable was to get rid of the
!PARAVIRT dependency.  I can add a follow-on here that will act as if we
did "nokaiser" whenever Xen is in play so we can remove this dependency.

I just hope Xen is detectable early enough to do the static patching.