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From: Jan Beulich <jbeulich@suse.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Juergen Gross <jgross@suse.com>
Subject: Re: [PATCH] x86/Xen: swap NX determination and GDT setup on BSP
Date: Fri, 21 May 2021 15:15:40 +0200	[thread overview]
Message-ID: <c2733c58-4514-6df0-3f0b-0f8b65132017@suse.com> (raw)
In-Reply-To: <0103d46f-4feb-e49d-f738-a2bf3d38c216@oracle.com>

On 21.05.2021 15:12, Boris Ostrovsky wrote:
> 
> On 5/21/21 3:45 AM, Juergen Gross wrote:
>> On 21.05.21 09:26, Jan Beulich wrote:
>>> On 21.05.2021 09:18, Juergen Gross wrote:
>>>> On 20.05.21 14:08, Jan Beulich wrote:
>>>>> On 20.05.2021 13:57, Juergen Gross wrote:
>>>>>> On 20.05.21 13:42, Jan Beulich wrote:
>>>>>>> xen_setup_gdt(), via xen_load_gdt_boot(), wants to adjust page tables.
>>>>>>> For this to work when NX is not available, x86_configure_nx() needs 
>> to
>>>>>>> be called first.
>>>>>>>
>>>>>>> Reported-by: Olaf Hering <olaf@aepfle.de>
>>>>>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>>>>>
>>>>>> Reviewed-by: Juergen Gross <jgross@suse.com>
>>>>>
>>>>> Thanks. I guess I forgot
>>>>>
>>>>> Cc: stable@vger.kernel.org
>>>>>
>>>>> If you agree, can you please add this before pushing to Linus?
>>>>
>>>> Uh, just had a look why x86_configure_nx() was called after
>>>> xen_setup_gdt().
>>>>
>>>> Upstream your patch will be fine, but before kernel 5.9 it will
>>>> break running as 32-bit PV guest (see commit 36104cb9012a82e7).
>>>
>>> Oh, indeed. That commit then actually introduced the issue here,
>>> and hence a Fixes: tag may be warranted.
>>
>> Added it already. :-)
>>
>> And I've limited the backport to happen not for 5.8 and older, of
>> course.
> 
> 
> Did something changed recently that this became a problem? That commit has been there for 3 years.

He happened to try on a system where NX was turned off in the BIOS. That's
not a setting you would usually find in use.


> Didn't Olaf report this to be a problem only on SLES kernels?

Which I assume have backports of the problematic change.

Jan


  reply	other threads:[~2021-05-21 13:15 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-20 11:42 Jan Beulich
2021-05-20 11:57 ` Juergen Gross
2021-05-20 12:08   ` Jan Beulich
2021-05-20 12:18     ` Juergen Gross
2021-05-21  7:18     ` Juergen Gross
2021-05-21  7:26       ` Jan Beulich
2021-05-21  7:45         ` Juergen Gross
2021-05-21 13:12           ` Boris Ostrovsky
2021-05-21 13:15             ` Jan Beulich [this message]
2021-05-21 13:17               ` Boris Ostrovsky
2021-05-21  8:30 ` Juergen Gross

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