From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: HVMlite ABI specification DRAFT A
Date: Thu, 4 Feb 2016 22:25:47 +0000
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To: Samuel Thibault <samuel.thibault@ens-lyon.org>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>, xen-devel <xen-devel@lists.xenproject.org>, Jan Beulich <JBeulich@suse.com>, David Vrabel <david.vrabel@citrix.com>, Paul Durrant <paul.durrant@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Wei Liu <wei.liu2@citrix.com>, Tim Deegan <tim@xen.org>
List-Id: xen-devel@lists.xenproject.org

On 04/02/2016 22:21, Samuel Thibault wrote:
> Boris Ostrovsky, on Thu 04 Feb 2016 14:18:46 -0500, wrote:
>> On 02/04/2016 02:09 PM, Samuel Thibault wrote:
>>> Roger Pau Monn=E9, on Thu 04 Feb 2016 18:48:14 +0100, wrote:
>>>>     struct hvm_start_info {
>>>>     #define HVM_START_MAGIC_VALUE 0x336ec578
>>>>         uint32_t magic;             /* Contains the magic value 0x336e=
c578       */
>>>>                                     /* ("xEn3" with the 0x80 bit of th=
e "E" set).*/
>>>>         uint32_t flags;             /* SIF_xxx flags.                 =
           */
>>>>         uint32_t cmdline_paddr;     /* Physical address of the command=
 line.     */
>>>>         uint32_t nr_modules;        /* Number of modules passed to the=
 kernel.   */
>>>>         uint32_t modlist_paddr;     /* Physical address of an array of=
           */
>>>>                                     /* hvm_modlist_entry.             =
           */
>>>>     };
>>> Mmm, don't we also need a description of the initial page table, so that
>>> the guest kernel knows which part of the memory it shouldn't use until
>>> having initialized its own page table?  Or is there none in the guest
>>> physical memory at startup of HVMlite mode?
>> We start with paging off.
> So a 32bit hypervisor *has* to use segmentation to protect itself from
> domU?

This is an HVM domain, so uses hardware virtualisation extensions.  It
is not like a PV guest.

The HVMLite binary is free to choose its width and paging mode.  All
this document states is that the entry point shall be 32bit flat unpaged
mode.

~Andrew