On 29/06/18 06:27, Jan Beulich wrote: >>>> Andrew Cooper <andrew.coop...@citrix.com> 06/28/18 6:10 PM >>> >> On 28/06/18 14:35, Jan Beulich wrote: >>>>>> On 26.06.18 at 13:35, <andrew.coop...@citrix.com> wrote: >>>> --- a/xen/arch/x86/Kconfig >>>> +++ b/xen/arch/x86/Kconfig >>>> @@ -161,3 +161,24 @@ endmenu >>>> source "common/Kconfig" >>>> >>>> source "drivers/Kconfig" >>>> + >>>> +menu "Deprecated Functionality" >>>> + >>>> +config LEGACY_PV_LDT_PAGING >>>> + def_bool n >>>> + prompt "PV LDT Paging-out support" >>>> + ---help--- >>>> + For a very long time, the PV ABI has included the ability to page >>>> + out the LDT by transitioning its mapping to not-present. This >>>> + functionality is believed to only exist for the PV Windows XP port >>>> + which never came to anything. >>>> + >>>> + The implementation contains a vCPU scalability limitation in a >>>> + position which is prohibitively complicated to resolve. As the >>>> + feature is believed to be unused in practice, removing the feature >>>> + is the easiest remediation. >>>> + >>>> + If you discover a usecase which is broken by this option being off, >>>> + please contact xen-devel@lists.xenproject.org urgently. Baring >>>> + something unexpected, the code and this option will be removed. >>> I think it should be said here explicitly when (or to be precise, no earlier >>> than when) this is going to happen. >> I'm open to suggests, but decided not to name a specific release (if >> only to avoid second-guessing our future numbering and release schedule). >> >>> I also think the security support status with the option enabled needs to >>> be clarified. Perhaps we'd go in stages: Introduce the (default off) option, >>> then (e.g. for 4.13) switch its use to security unsupported, and finally >>> drop the code (e.g. for 4.14). >> I presume you mean that we should hide it behind EXPERT at that point? > That's the best way to express it I guess, yes. Plus some form of remark in > SUPPORT.md. > > >> What does the middle step gets us. If its going to be off by default >> and unable to be enabled by default, that is as good as deleted. > Think of people only using released code: They'd notice the removed > functionality only in 4.12. Removing the code right away for 4.13 could > therefore be too early.
How can we unblock this patch? I stand by my original point of "that's as good as deleted and isn't actually useful for distros". CC'ing the rest. ~Andrew
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