linux-kernel - Re: [Xen-devel] [PATCH 4/4] xen/PVH: Remove reserved entry in PVH GDT

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Message-ID: <5a357f3d-b66e-ca55-0601-18a89b549f4a@oracle.com>
Date:   Tue, 1 May 2018 08:34:53 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Roger Pau Monné <roger.pau@...rix.com>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        jgross@...e.com
Subject: Re: [Xen-devel] [PATCH 4/4] xen/PVH: Remove reserved entry in PVH GDT

On 05/01/2018 04:00 AM, Roger Pau Monné wrote:
> On Mon, Apr 30, 2018 at 12:23:39PM -0400, Boris Ostrovsky wrote:
>> And without it we can't use _BOOT_XX macros any longer so define new ones.
> 
> Not being that familiar with Linux internals I'm not sure I see the
> benefit of this. Isn't there a risk that some other code is going to
> use the __BOOT_XX defines?

The startup code we are jumping to loads their own GDT and I don't see 
any explicit references to segments.

The reason I added this patch was that since we are adding another 
segment descriptor (GS) we are now using PVH-specific GDT and so we are 
not sharing layout with other code anymore. (Also, the new GS segment 
overlaps with __BOOT_TSS so I kind of broke it already there, not 
unintentionally).

But if people think I should stick with __BOOT_XX I can drop this patch 
(and then probably move GS down one entry).

-boris