[RFC PATCH 33/43] KVM: PPC: Book3S HV P9: More SPR speed improvements

[Nicholas Piggin <npiggin@gmail.com>]

This avoids more scoreboard stalls and reduces mtSPRs.

-193 cycles (6985) POWER9 virt-mode NULL hcall

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kvm/book3s_hv_p9_entry.c | 67 ++++++++++++++++-----------
 1 file changed, 40 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index b41be3d8f101..4d1a2d1ff4c1 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -618,24 +618,29 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 		vc->tb_offset_applied = vc->tb_offset;
 	}
 
-	if (vc->pcr)
-		mtspr(SPRN_PCR, vc->pcr | PCR_MASK);
-	mtspr(SPRN_DPDES, vc->dpdes);
 	mtspr(SPRN_VTB, vc->vtb);
-
 	mtspr(SPRN_PURR, vcpu->arch.purr);
 	mtspr(SPRN_SPURR, vcpu->arch.spurr);
 
+	if (vc->pcr)
+		mtspr(SPRN_PCR, vc->pcr | PCR_MASK);
+	if (vc->dpdes)
+		mtspr(SPRN_DPDES, vc->dpdes);
+
 	if (dawr_enabled()) {
-		mtspr(SPRN_DAWR0, vcpu->arch.dawr0);
-		mtspr(SPRN_DAWRX0, vcpu->arch.dawrx0);
+		if (vcpu->arch.dawr0 != host_dawr0)
+			mtspr(SPRN_DAWR0, vcpu->arch.dawr0);
+		if (vcpu->arch.dawrx0 != host_dawrx0)
+			mtspr(SPRN_DAWRX0, vcpu->arch.dawrx0);
 		if (cpu_has_feature(CPU_FTR_DAWR1)) {
-			mtspr(SPRN_DAWR1, vcpu->arch.dawr1);
-			mtspr(SPRN_DAWRX1, vcpu->arch.dawrx1);
+			if (vcpu->arch.dawr1 != host_dawr1)
+				mtspr(SPRN_DAWR1, vcpu->arch.dawr1);
+			if (vcpu->arch.dawrx1 != host_dawrx1)
+				mtspr(SPRN_DAWRX1, vcpu->arch.dawrx1);
 		}
 	}
-	mtspr(SPRN_CIABR, vcpu->arch.ciabr);
-	mtspr(SPRN_IC, vcpu->arch.ic);
+	if (vcpu->arch.ciabr != host_ciabr)
+		mtspr(SPRN_CIABR, vcpu->arch.ciabr);
 
 	mtspr(SPRN_PSSCR, vcpu->arch.psscr | PSSCR_EC |
 	      (local_paca->kvm_hstate.fake_suspend << PSSCR_FAKE_SUSPEND_LG));
@@ -833,17 +838,6 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	vc->dpdes = mfspr(SPRN_DPDES);
 	vc->vtb = mfspr(SPRN_VTB);
 
-	save_clear_guest_mmu(kvm, vcpu);
-	switch_mmu_to_host(kvm, host_pidr);
-
-	/*
-	 * If we are in real mode, only switch MMU on after the MMU is
-	 * switched to host, to avoid the P9_RADIX_PREFETCH_BUG.
-	 */
-	__mtmsrd(msr, 0);
-
-	store_vcpu_state(vcpu);
-
 	dec = mfspr(SPRN_DEC);
 	if (!(lpcr & LPCR_LD)) /* Sign extend if not using large decrementer */
 		dec = (s32) dec;
@@ -861,6 +855,19 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 		vc->tb_offset_applied = 0;
 	}
 
+	save_clear_guest_mmu(kvm, vcpu);
+	switch_mmu_to_host(kvm, host_pidr);
+
+	/*
+	 * Enable MSR here in order to have facilities enabled to save
+	 * guest registers. This enables MMU (if we were in realmode), so
+	 * only switch MMU on after the MMU is switched to host, to avoid
+	 * the P9_RADIX_PREFETCH_BUG or hash guest context.
+	 */
+	__mtmsrd(msr, 0);
+
+	store_vcpu_state(vcpu);
+
 	mtspr(SPRN_PURR, local_paca->kvm_hstate.host_purr);
 	mtspr(SPRN_SPURR, local_paca->kvm_hstate.host_spurr);
 
@@ -868,15 +875,21 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	mtspr(SPRN_PSSCR, host_psscr |
 	      (local_paca->kvm_hstate.fake_suspend << PSSCR_FAKE_SUSPEND_LG));
 	mtspr(SPRN_HFSCR, host_hfscr);
-	mtspr(SPRN_CIABR, host_ciabr);
-	mtspr(SPRN_DAWR0, host_dawr0);
-	mtspr(SPRN_DAWRX0, host_dawrx0);
+	if (vcpu->arch.ciabr != host_ciabr)
+		mtspr(SPRN_CIABR, host_ciabr);
+	if (vcpu->arch.dawr0 != host_dawr0)
+		mtspr(SPRN_DAWR0, host_dawr0);
+	if (vcpu->arch.dawrx0 != host_dawrx0)
+		mtspr(SPRN_DAWRX0, host_dawrx0);
 	if (cpu_has_feature(CPU_FTR_DAWR1)) {
-		mtspr(SPRN_DAWR1, host_dawr1);
-		mtspr(SPRN_DAWRX1, host_dawrx1);
+		if (vcpu->arch.dawr1 != host_dawr1)
+			mtspr(SPRN_DAWR1, host_dawr1);
+		if (vcpu->arch.dawrx1 != host_dawrx1)
+			mtspr(SPRN_DAWRX1, host_dawrx1);
 	}
 
-	mtspr(SPRN_DPDES, 0);
+	if (vc->dpdes)
+		mtspr(SPRN_DPDES, 0);
 	if (vc->pcr)
 		mtspr(SPRN_PCR, PCR_MASK);
 
-- 
2.23.0