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Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace
 page tables
To: Ingo Molnar <mingo@kernel.org>
References: <20171031223146.6B47C861@viggo.jf.intel.com>
 <20171101085424.cwvc4nrrdhvjc3su@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        "H. Peter Anvin" <hpa@zytor.com>, borisBrian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Thomas Garnier <thgarnie@google.com>, Kees Cook <keescook@google.com>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <d7cb1705-5ef0-5f6e-b1cf-e3f28e998477@linux.intel.com>
Date: Wed, 1 Nov 2017 15:14:11 -0700
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On 11/01/2017 01:54 AM, Ingo Molnar wrote:
> Beyond the inevitable cavalcade of (solvable) problems that will pop up during 
> review, one major item I'd like to see addressed is runtime configurability: it 
> should be possible to switch between a CR3-flushing and a regular syscall and page 
> table model on the admin level, without restarting the kernel and apps. Distros 
> really, really don't want to double the number of kernel variants they have.
> 
> The 'Kaiser off' runtime switch doesn't have to be as efficient as 
> CONFIG_KAISER=n, at least initialloy, but at minimum it should avoid the most 
> expensive page table switching paths in the syscall entry codepaths.

Due to popular demand, I went and implemented this today.  It's not the
prettiest code I ever wrote, but it's pretty small.

Just in case anyone wants to play with it, I threw a snapshot of it up here:

> https://git.kernel.org/pub/scm/linux/kernel/git/daveh/x86-kaiser.git/log/?h=kaiser-dynamic-414rc6-20171101

I ran some quick tests.  When CONFIG_KAISER=y, but "echo 0 >
kaiser-enabled", the tests that I ran were within the noise vs. a
vanilla kernel, and that's with *zero* optimization.