tree afdbb0c64c15ec522eae260949bfec02df2291b2
parent b80119bb35a49a4e8dbfb9708872adfd5cf38dee
author Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> 1240558010 -0700
committer Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> 1241823324 -0700

xen: cache cr0 value to avoid trap'n'emulate for read_cr0

stts() is implemented in terms of read_cr0/write_cr0 to update the
state of the TS bit.  This happens during context switch, and so
is fairly performance critical.  Rather than falling back to
a trap-and-emulate native read_cr0, implement our own by caching
the last-written value from write_cr0 (the TS bit is the only one
we really care about).

Impact: optimise Xen context switches
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>