The ability to run nested guests under KVM means that a guest can also
act as a hypervisor for it's own nested guest. Currently
ppc_set_pmu_inuse() assumes that either FW_FEATURE_LPAR is set,
indicating a guest environment, and so sets the pmcregs_in_use flag in
the lppaca, or that it isn't set, indicating a hypervisor environment,
and so sets the pmcregs_in_use flag in the paca.

The pmcregs_in_use flag in the lppaca is used to communicate this
information to a hypervisor and so must be set in a guest environment.
The pmcregs_in_use flag in the paca is used by KVM code to determine
whether the host state of the performance monitoring unit (PMU) must
be saved and restored when running a guest.

Thus when a guest also acts as a hypervisor it must set this bit in
both places since it needs to ensure both that the real hypervisor
saves it's PMU registers when it runs (requires pmcregs_in_use flag in
lppaca), and that it saves it's own PMU registers when running a
nested guest (requires pmcregs_in_use flag in paca).

Modify ppc_set_pmu_inuse() so that the pmcregs_in_use bit is set in
both the lppaca and the paca when a guest (LPAR) is running with the
capability of running it's own guests (CONFIG_KVM_BOOK3S_HV_POSSIBLE).

Fixes: 95a6432c ("KVM: PPC: Book3S HV: Streamlined guest entry/exit path on P9 for radix guests")
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190703012022.15644-2-sjitindarsingh@gmail.com