[PATCH v1 49/55] KVM: PPC: Book3S HV P9: Optimise hash guest SLB saving

[Nicholas Piggin]

slbmfee/slbmfev instructions are very expensive, moreso than a regular
mfspr instruction, so minimising them significantly improves hash guest
exit performance. The slbmfev is only required if slbmfee found a valid
SLB entry.

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/kvm/book3s_hv_p9_entry.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c 
b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 1287dac918a0..338873f90c72 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -477,10 +477,22 @@ static void __accumulate_time(struct kvm_vcpu *vcpu, 
struct kvmhv_tb_accumulator
 #define accumulate_time(vcpu, next) do {} while (0)
 #endif
 
-static inline void mfslb(unsigned int idx, u64 *slbee, u64 *slbev)
+static inline u64 mfslbv(unsigned int idx)
 {
-       asm volatile("slbmfev  %0,%1" : "=r" (*slbev) : "r" (idx));
-       asm volatile("slbmfee  %0,%1" : "=r" (*slbee) : "r" (idx));
+       u64 slbev;
+
+       asm volatile("slbmfev  %0,%1" : "=r" (slbev) : "r" (idx));
+
+       return slbev;
+}
+
+static inline u64 mfslbe(unsigned int idx)
+{
+       u64 slbee;
+
+       asm volatile("slbmfee  %0,%1" : "=r" (slbee) : "r" (idx));
+
+       return slbee;
 }
 
 static inline void mtslb(u64 slbee, u64 slbev)
@@ -610,8 +622,10 @@ static void save_clear_guest_mmu(struct kvm *kvm, struct 
kvm_vcpu *vcpu)
                 */
                for (i = 0; i < vcpu->arch.slb_nr; i++) {
                        u64 slbee, slbev;
-                       mfslb(i, &slbee, &slbev);
+
+                       slbee = mfslbe(i);
                        if (slbee & SLB_ESID_V) {
+                               slbev = mfslbv(i);
                                vcpu->arch.slb[nr].orige = slbee | i;
                                vcpu->arch.slb[nr].origv = slbev;
                                nr++;
-- 
2.23.0