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Date: Wed, 1 Nov 2017 15:14:11 -0700 From: Dave Hansen <dave.hansen@...ux.intel.com> To: Ingo Molnar <mingo@...nel.org> Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, Andy Lutomirski <luto@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, "H. Peter Anvin" <hpa@...or.com>, borisBrian Gerst <brgerst@...il.com>, Denys Vlasenko <dvlasenk@...hat.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Thomas Garnier <thgarnie@...gle.com>, Kees Cook <keescook@...gle.com> Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables 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.
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