Re: [Xen-devel] [PATCH for-4.6] x86/gdt: Drop write-only, xalloc()'d array from set_gdt()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 04/08/15 14:59, Ian Campbell wrote:
> On Tue, 2015-08-04 at 10:34 +0100, Wei Liu wrote:
>> On Mon, Aug 03, 2015 at 06:05:43PM +0100, Andrew Cooper wrote:
>>> It is not used, and can cause a spurious failure of the set_gdt() 
>>> hypercall in
>>> low memory situations.
>>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> ---
>>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>>> ---
>> This array does appear to be write-only and never gets read.
>>
>> FWIW
>>
>> Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> The use was removed by:
>
> commit 5889a3e1d123bdad4a3d150310d647db55459966
> Author: Tim Deegan <tim@xxxxxxx>
> Date:   Thu May 17 10:24:54 2012 +0100
>
>     x86/mm: Use get_page_from_gfn() instead of get_gfn()/put_gfn.
>     
>     Signed-off-by: Tim Deegan <tim@xxxxxxx>
>     Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
>
> after it was introduced by:
>
> commit 51032ca058e43fbd37ea1f7c7c003496f6451340
> Author: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
> Date:   Fri Nov 11 18:11:34 2011 +0000
>
>     Modify naming of queries into the p2m
>     [...]
>     Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
>     Acked-by: Tim Deegan <tim@xxxxxxx>
>     Committed-by: Keir Fraser <keir@xxxxxxx>
>
>> It's obviously correct and fixes a problem, so it can be applied to 4.6
>> tree.
> FWIW I think so too, but I'm hesitant to apply without a maintainer(/Jan)'s
> ack. I think this can probably wait until next week? 
>
>>>  xen/arch/x86/mm.c |    9 +--------
> George is the current "X86 MEMORY MANAGEMENT" maintainer, which is
> xen/arch/x86/mm/*, should xen/arch/x86/mm.c be included there too?

Oops - I hadn't even twigged.

Despite being in mm.c, this really isn't memory management and is just
general x86 behaviour, which is covered by my maintership role.

Not that I expect anyone (maintainer or not) to have a problem with this
change.

FWIW, following the Linux LDT thread, I have a bucket load of changes to
do with GDT and LDT handling for PV guests.  While most of that is
definitely 4.7 material, I felt that this fix alone should be fixed in 4.6

~Andrew

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