Re: [Xen-devel] [PATCH 4/5] x86/pv: Drop support for paging out the LDT

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.01.18 at 11:38, <dunlapg@xxxxxxxxx> wrote:
> On Thu, Jan 18, 2018 at 7:59 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 12.01.18 at 19:37, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/domain.c
>>> +++ b/xen/arch/x86/domain.c
>>> @@ -1942,11 +1942,8 @@ int domain_relinquish_resources(struct domain *d)
>>>          {
>>>              for_each_vcpu ( d, v )
>>>              {
>>> -                /*
>>> -                 * Relinquish GDT mappings. No need for explicit unmapping 
>>> of
>>> -                 * the LDT as it automatically gets squashed with the guest
>>> -                 * mappings.
>>> -                 */
>>> +                /* Relinquish GDT/LDT mappings. */
>>> +                pv_destroy_ldt(v);
>>>                  pv_destroy_gdt(v);
>>
>> The domain is dead at this point, so the order doesn't matter much,
>> but strictly speaking you should destroy the GDT before destroying
>> the LDT (just like LDT _loads_ always need to come _after_ GDT
>> adjustments).
>>
>> Everything else here looks fine, but the initial comment may need
>> further discussion. For example we may want to consider a
>> two-stage phasing out of the feature, with a couple of years in
>> between: Make the functionality dependent upon a default-off
>> command line option for the time being, and issue a bright warning
>> when someone actually enables it (telling them to tell us).
> 
> One of the problems we have is that people seem to wait for 2-3 years
> after a release has been made to start updating to it.  So we'd have
> to leave such a warning for probably 5 years minimum.

That's a reasonable time frame imo for phasing out something that's
a de-facto part of an ABI.

Jan


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