[PATCH v2 20/37] KVM: PPC: Book3S HV P9: Reduce mftb per guest entry/exit

[Nicholas Piggin]

mftb is serialising (dispatch next-to-complete) so it is heavy weight
for a mfspr. Avoid reading it multiple times in the entry or exit paths.
A small number of cycles delay to timers is tolerable.

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 735ec40ece86..d98958b78830 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3689,7 +3689,7 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, 
u64 time_limit,
        if (!(vcpu->arch.ctrl & 1))
                mtspr(SPRN_CTRLT, mfspr(SPRN_CTRLF) & ~1);
 
-       mtspr(SPRN_DEC, vcpu->arch.dec_expires - mftb());
+       mtspr(SPRN_DEC, vcpu->arch.dec_expires - tb);
 
        if (kvmhv_on_pseries()) {
                /*
@@ -3822,7 +3822,7 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, 
u64 time_limit,
        vc->entry_exit_map = 0x101;
        vc->in_guest = 0;
 
-       mtspr(SPRN_DEC, local_paca->kvm_hstate.dec_expires - mftb());
+       mtspr(SPRN_DEC, local_paca->kvm_hstate.dec_expires - tb);
        mtspr(SPRN_SPRG_VDSO_WRITE, local_paca->sprg_vdso);
 
        kvmhv_load_host_pmu();
-- 
2.23.0