lguest: clear cached last cpu when guest_set_pgd() called.
lguest: clear cached last cpu when guest_set_pgd() called.

commit v3.9-rc1-53-g6d0cda9 "lguest: cache last cpu we ran on." missed
one case, which causes a triple fault.  The guest calls guest_set_pgd()
on the top page, and we carefully remap the Switcher text page.  But
we didn't reset last_host_cpu, so map_switcher_in_guest() thinks
the guest's regs and IDT/GDT etc are already mapped.

Reported-by: Paul Bolle <0bda9a89324ffe2d19adec61a9f1cd9f8c8e45f0@tiscali.nl>
Tested-by: Paul Bolle <0bda9a89324ffe2d19adec61a9f1cd9f8c8e45f0@tiscali.nl>
Signed-off-by: Rusty Russell <df9728c9e5104131c08c7adb03af425394842596@rustcorp.com.au>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas