linux-kernel - Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables

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Date:   Thu, 2 Nov 2017 12:38:05 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace
 page tables

On 11/02/2017 12:01 PM, Will Deacon wrote:
> On Tue, Oct 31, 2017 at 03:31:46PM -0700, Dave Hansen wrote:
>> KAISER makes it harder to defeat KASLR, but makes syscalls and
>> interrupts slower.  These patches are based on work from a team at
>> Graz University of Technology posted here[1].  The major addition is
>> support for Intel PCIDs which builds on top of Andy Lutomorski's PCID
>> work merged for 4.14.  PCIDs make KAISER's overhead very reasonable
>> for a wide variety of use cases.
> I just wanted to say that I've got a version of this up and running for
> arm64. I'm still ironing out a few small details, but I hope to post it
> after the merge window. We always use ASIDs, and the perf impact looks
> like it aligns roughly with your findings for a PCID-enabled x86 system.

Welcome to the party!

I don't know if you've found anything different, but there been woefully
little code that's really cross-architecture.  The kernel task
stack-mapping stuff _was_, but it's going away.  The per-cpu-user-mapped
section stuff might be common, I guess.

Is there any other common infrastructure that we can or should be sharing?