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Date:   Thu, 1 Mar 2018 10:23:40 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Maran Wilson <maran.wilson@oracle.com>
Cc:     pbonzini@redhat.com, jgross@suse.com, boris.ostrovsky@oracle.com,
        roger.pau@citrix.com, andrew.cooper3@citrix.com, hch@infradead.org,
        JBeulich@suse.com, x86@kernel.org, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        thomas.lendacky@amd.com, dave.hansen@linux.intel.com,
        rkrcmar@redhat.com, gregkh@linuxfoundation.org, mchehab@kernel.org,
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        tglx@linutronix.de, bp@suse.de, davem@davemloft.net,
        kirill.shutemov@linux.intel.com
Subject: Re: [Xen-devel] [RFC PATCH v4 6/7] xen/pvh: Add memory map pointer
 to hvm_start_info struct
Message-ID: <20180301152340.GI15623@char.us.oracle.com>
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 <1519842483-8887-7-git-send-email-maran.wilson@oracle.com>
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On Wed, Feb 28, 2018 at 10:28:02AM -0800, Maran Wilson wrote:
> The start info structure that is defined as part of the x86/HVM direct boot
> ABI and used for starting Xen PVH guests would be more versatile if it also
> included a way to pass information about the memory map to the guest. This
> would allow KVM guests to share the same entry point.
> 
> Signed-off-by: Maran Wilson <maran.wilson@oracle.com>
> ---
>  include/xen/interface/hvm/start_info.h | 50 +++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/include/xen/interface/hvm/start_info.h b/include/xen/interface/hvm/start_info.h
> index 648415976ead..80cfbd35c1af 100644
> --- a/include/xen/interface/hvm/start_info.h
> +++ b/include/xen/interface/hvm/start_info.h
> @@ -33,7 +33,7 @@
>   *    | magic          | Contains the magic value XEN_HVM_START_MAGIC_VALUE
>   *    |                | ("xEn3" with the 0x80 bit of the "E" set).
>   *  4 +----------------+
> - *    | version        | Version of this structure. Current version is 0. New
> + *    | version        | Version of this structure. Current version is 1. New

Have you checked if there are any OSes that end up checking this value at all?

Perhaps also expand the comment to say that for PV guests only 0 is allowed.
For PVH 0 or 1 is allowed ?