linux-kernel - Re: [Xen-devel] [PATCH v6 10/34] x86, x86/mm, x86/xen, olpc: Use __va() against just the physical address in cr3

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Date:   Fri, 9 Jun 2017 19:54:04 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        <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>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>
CC:     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>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        xen-devel <xen-devel@...ts.xen.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [Xen-devel] [PATCH v6 10/34] x86, x86/mm, x86/xen, olpc: Use
 __va() against just the physical address in cr3

On 09/06/17 19:43, Boris Ostrovsky wrote:
> On 06/09/2017 02:36 PM, Tom Lendacky wrote:
>>> basis, although (as far as I am aware) Xen as a whole would be able to
>>> encompass itself and all of its PV guests inside one single SME
>>> instance.
>> Yes, that is correct.

Thinking more about this, it would only be possible if all the PV guests
were SME-aware and understood not to choke when it finds a frame with a
high address bit set.

I expect the only viable way to implement this (should we wish) is to
have PV guests explicitly signal support (probably via an ELF note),
after which it needs to know about the existence of SME, the meaning of
the encrypted bit in PTEs, and to defer all configuration responsibility
to Xen.

~Andrew