FROMGIT: KVM: arm64: Really propagate PSCI SYSTEM_RESET2 arguments to userspace

Commit d43583b8 ("KVM: arm64: Expose PSCI SYSTEM_RESET2 call to the
guest") hooked up the SYSTEM_RESET2 PSCI call for guests but failed to
preserve its arguments for userspace, instead overwriting them with
zeroes via smccc_set_retval(). As Linux only passes zeroes for these
arguments, this appeared to be working for Linux guests. Oh well.

Don't call smccc_set_retval() for a SYSTEM_RESET2 heading to userspace
and instead set X0 (and only X0) explicitly to PSCI_RET_INTERNAL_FAILURE
just in case the vCPU re-enters the guest.

Fixes: d43583b8 ("KVM: arm64: Expose PSCI SYSTEM_RESET2 call to the guest")
Reported-by: Andrew Walbran <qwandor@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220309181308.982-1-will@kernel.org
(cherry picked from commit 9d3e7b7c
 git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git

 next)
Bug: 216801012
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: Ieead1a813e6b4dfee1aa89e42ee1926efcd5f590