linux-kernel - Re: [PATCH v6 25/34] swiotlb: Add warnings for use of bounce buffers with SME

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Message-ID: <20170608075829.GA2446@infradead.org>
Date:   Thu, 8 Jun 2017 00:58:29 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Tom Lendacky <thomas.lendacky@....com>
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, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org, Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v6 25/34] swiotlb: Add warnings for use of bounce buffers
 with SME

On Wed, Jun 07, 2017 at 02:17:32PM -0500, Tom Lendacky wrote:
> Add warnings to let the user know when bounce buffers are being used for
> DMA when SME is active.  Since the bounce buffers are not in encrypted
> memory, these notifications are to allow the user to determine some
> appropriate action - if necessary.

And what would the action be?  Do we need a boot or other option to
disallow this fallback for people who care deeply?