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

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Message-ID: <20171102190106.GC22263@arm.com>
Date:   Thu, 2 Nov 2017 19:01:07 +0000
From:   Will Deacon <will.deacon@....com>
To:     Dave Hansen <dave.hansen@...ux.intel.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

Hi Dave,

[+linux-arm-kernel]

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.

Cheers,

Will