Xen devel - Feb 2011 - [RFC PATCH] revive VCPUOP_register_time_memory_area

Hi all,

the attached patch tries to revive the support for userspace 
vcpu_time_info.  Writing the information is done after context switch to 
prevent the memory corruption that led to the disabling of the hypercall.

The patch also fixes the write of version_update_begin(_u.version) into 
the userspace vcpu_time_info.

A while ago, Jeremy wrote that he was "not sure that the Xen clock 
algorithm can give strict enough monotonicity for usermode use".  Has 
anybody else ever put some thought into this, and maybe shared (or not 
shared) his worries?

The patch is mostly untested because Xen 4.1 fails to boot the 
(non-pvops) dom0 kernels I have around; a very similar patch _was_ 
tested though and worked. :)

Paolo


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