linux-kernel - Re: AMD SME encrpytion and PCI BAR pages to user space

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Message-ID: <20201019170029.GU6219@nvidia.com>
Date:   Mon, 19 Oct 2020 14:00:29 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Tom Lendacky <thomas.lendacky@....com>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arch@...r.kernel.org>, <linux-mm@...ck.org>,
        <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "Andy Lutomirski" <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        "Dave Young" <dyoung@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: AMD SME encrpytion and PCI BAR pages to user space

On Mon, Oct 19, 2020 at 11:36:16AM -0500, Tom Lendacky wrote:

> > Is RDMA missing something? I don't see anything special in VFIO for
> > instance and the two are very similar - does VFIO work with SME, eg
> > DPDK or something unrelated to virtualization?
> 
> If user space is mapping un-encrypted memory, then, yes, it would seem
> that there is a gap in the support where the pgprot_decrypted() would be
> needed in order to override the protection map.

It isn't "memory" it is PCI BAR pages, eg memory mapped IO

> > Is there a reason not to just add prot_decrypted() to
> > io_remap_pfn_range()? Is there use cases where a caller actually wants
> > encrypted io memory?
> 
> As long as you never have physical memory / ram being mapped in this path,
> it seems that applying pgprot_decrypted() would be ok.

I think the word 'io' implies this is the case..

Let me make a patch for this avenue then, I think it is not OK to add
pgprot_decrypted to every driver.. We already have the special
distinction with io and non-io remap, that seems better.

> > I saw your original patch series edited a few drivers this way, but
> > not nearly enough. So I feel like I'm missing something.. Does vfio
> > work with SME? I couldn't find any sign of it calling prot_decrypted()
> > either?
> 
> I haven't tested SME with VFIO/DPDK.

Hum, I assume it is broken also. Actually quite a swath of drivers
and devices will be broken under this :\

Jason