linux-kernel - Re: [PATCH V1 3/6] xen/virtio: Add option to restrict memory access under Xen

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Message-ID: <YmcR5bfaYh1z7VUq@zn.tnic>
Date:   Mon, 25 Apr 2022 23:25:57 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Oleksandr <olekstysh@...il.com>
Cc:     Juergen Gross <jgross@...e.com>,
        Christoph Hellwig <hch@...radead.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Julien Grall <julien@....org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH V1 3/6] xen/virtio: Add option to restrict memory access
 under Xen

On Mon, Apr 25, 2022 at 11:38:36PM +0300, Oleksandr wrote:
> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
> index efd8205..d06bc7a 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -72,6 +72,19 @@ enum cc_attr {
>          * Examples include TDX guest & SEV.
>          */
>         CC_ATTR_GUEST_UNROLL_STRING_IO,
> +
> +       /**
> +        * @CC_ATTR_GUEST_MEM_ACCESS_RESTRICTED: Restricted memory access to
> +        *                                       Guest memory is active
> +        *
> +        * The platform/OS is running as a guest/virtual machine and uses
> +        * the restricted access to its memory. This attribute is set if
> either
> +        * Guest memory encryption or restricted memory access using Xen
> grant
> +        * mappings is active.
> +        *
> +        * Examples include Xen guest and SEV.

Wait, whaaat?

The cc_platform* stuff is for *confidential computing* guests to check
different platform aspects.

>From quickly skimming over this, this looks like a misuse to me.

Why can't you query this from the hypervisor just like you do your other
querying about what is supported, etc? Hypercalls, CPUID, whatever...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette