Support of old Xen versions in the Linux kernel

[Juergen Gross <jgross@xxxxxxxx>]

In x86 kernel development the question came up whether we need to
support XENFEAT_gnttab_map_avail_bits not being set when running as a PV
guest.

This feature is active for PV guests since Xen 3.4.

So the basic question is: which is the oldest version of Xen we want to
support in the Linux kernel? As far as I know there is no Xen based
product in productive use with Xen older than 4.2.

Would we be fine to drop support for older versions (feel free to
suggest other versions than 4.2 as the first to be supported Xen
version)?

In case the answer is yes, I'd post some patches to clean up the kernel,
including a safety net to bail out in case a feature needed isn't
available.


Juergen

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