linux-kernel - Re: [PATCH v9 00/38] x86: Secure Memory Encryption (AMD)

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Message-ID: <fce185d2-4420-7255-6331-6231c643c8c7@amd.com>
Date:   Mon, 10 Jul 2017 13:04:11 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, xen-devel@...ts.xen.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Brijesh Singh <brijesh.singh@....com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Alexander Potapenko <glider@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dave Young <dyoung@...hat.com>, Rik van Riel <riel@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v9 00/38] x86: Secure Memory Encryption (AMD)



On 7/8/2017 4:24 AM, Ingo Molnar wrote:
> 
> * Tom Lendacky <thomas.lendacky@....com> wrote:
> 
>> This patch series provides support for AMD's new Secure Memory Encryption (SME)
>> feature.
> 
> I'm wondering, what's the typical performance hit to DRAM access latency when SME
> is enabled?

It's about an extra 10 cycles of DRAM latency when performing an
encryption or decryption operation.

> 
> On that same note, if the performance hit is noticeable I'd expect SME to not be
> enabled in native kernels typically - but still it looks like a useful hardware

In some internal testing we've seen about 1.5% or less reduction in
performance. Of course it all depends on the workload: the number of
memory accesses, cache friendliness, etc.

> feature. Since it's controlled at the page table level, have you considered
> allowing SME-activated vmas via mmap(), even on kernels that are otherwise not
> using encrypted DRAM?

That is definitely something to consider as an additional SME-related
feature and something I can look into after this.

Thanks,
Tom

> 
> One would think that putting encryption keys into such encrypted RAM regions would
> generally improve robustness against various physical space attacks that want to
> extract keys but don't have full control of the CPU.
> 
> Thanks,
> 
> 	Ingo
>