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Wed, 2 May 2018 11:28:23 -0400 Received: from smtp.ctxuk.citrix.com ([185.25.65.24]:10155 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751941AbeEBP2U (ORCPT ); Wed, 2 May 2018 11:28:20 -0400 X-IronPort-AV: E=Sophos;i="5.49,354,1520899200"; d="scan'208";a="72507851" Subject: Re: [Xen-devel] [PATCH 2/4] xen/PVH: Use proper CS selector in long mode To: Jan Beulich , Boris Ostrovsky CC: Juergen Gross , xen-devel , , References: <20180430162339.17143-1-boris.ostrovsky@oracle.com> <20180430162339.17143-3-boris.ostrovsky@oracle.com> <5AE9713D02000078001C007B@prv1-mh.provo.novell.com> <6b7a748d-e289-c370-123a-678c6ad7d9dd@oracle.com> <5AE9D27402000078001C02ED@prv1-mh.provo.novell.com> <5AE9D49B02000078001C0322@prv1-mh.provo.novell.com> From: Andrew Cooper Openpgp: preference=signencrypt Message-ID: Date: Wed, 2 May 2018 16:28:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <5AE9D49B02000078001C0322@prv1-mh.provo.novell.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Language: en-GB X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To AMSPEX02CL02.citrite.net (10.69.22.126) Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 02/05/18 16:09, Jan Beulich wrote: >>>> On 02.05.18 at 17:08, wrote: >> On 05/02/2018 11:00 AM, Jan Beulich wrote: >>>>>> On 02.05.18 at 16:57, wrote: >>>> On 05/02/2018 04:05 AM, Jan Beulich wrote: >>>>>>>> On 30.04.18 at 18:23, wrote: >>>>>> Signed-off-by: Boris Ostrovsky >>>>> Reviewed-by: Jan Beulich >>>>> >>>>> 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. >> >> Oh, right. My theory was that we were picking up something from the >> stack (which is where 12th entry would be pointing) and the L bit, which >> I think is the only one we'd care about, happened to always be set there. > I don't think the L bit is the only one we care about, as I don't think you > can load a non-code selector into CS (even if none of the attributes are > later used for anything). The type/s/dpl/p/d/l attributes still very much matter even in 64bit. ~Andrew