linux-kernel - Re: [Xen-devel] [PATCH 2/4] xen/PVH: Use proper CS selector in long mode

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Message-Id: <5AE9D27402000078001C02ED@prv1-mh.provo.novell.com>
Date:   Wed, 02 May 2018 09:00:04 -0600
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Boris Ostrovsky" <boris.ostrovsky@...cle.com>
Cc:     "xen-devel" <xen-devel@...ts.xenproject.org>,
        "Juergen Gross" <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/4] xen/PVH: Use proper CS selector in
 long mode

>>> On 02.05.18 at 16:57, <boris.ostrovsky@...cle.com> wrote:
> On 05/02/2018 04:05 AM, Jan Beulich wrote:
>>>>> On 30.04.18 at 18:23, <boris.ostrovsky@...cle.com> wrote:
>>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> Reviewed-by: Jan Beulich <jbeulich@...e.com>
>>
>> But to understand why things have been working nevertheless it would
>> have been nice if the commit message wasn't empty, but instead said
>> something like "The two happen to be identical on 64-bit."
> 
> 
> Why do you think they are identical? __KERNEL_CS points to entry#12
> (which we don't specify in PVH GDT) while __BOOT_CS is the second entry
> (which we do create).

That's 32-bit's __KERNEL_CS. If the two weren't identical, the ljmp
you adjust would never have worked afaict.

Jan