[RFC PATCH 35/43] KVM: PPC: Book3S HV P9: Demand fault TM facility registers

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Use HFSCR facility disabling to implement demand faulting for TM, with
a hysteresis counter similar to the load_fp etc counters in context
switching that implement the equivalent demand faulting for userspace
facilities.

This speeds up guest entry/exit by avoiding the register save/restore
when a guest is not frequently using them. When a guest does use them
often, there will be some additional demand fault overhead, but these
are not commonly used facilities.

-304 cycles (6681) POWER9 virt-mode NULL hcall with the previous patch

Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
 arch/powerpc/include/asm/kvm_host.h   |  1 +
 arch/powerpc/kvm/book3s_hv.c          | 21 +++++++++++++++++----
 arch/powerpc/kvm/book3s_hv_nested.c   |  2 +-
 arch/powerpc/kvm/book3s_hv_p9_entry.c | 18 ++++++++++++------
 4 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index bee95106c1f2..d79f0b1b1578 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -586,6 +586,7 @@ struct kvm_vcpu_arch {
 	ulong ppr;
 	u32 pspb;
 	u8 load_ebb;
+	u8 load_tm;
 	ulong fscr;
 	ulong shadow_fscr;
 	ulong ebbhr;
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 99e9da078e7d..2430725f29f7 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1373,6 +1373,13 @@ static int kvmppc_ebb_unavailable(struct kvm_vcpu *vcpu)
 	return RESUME_GUEST;
 }
 
+static int kvmppc_tm_unavailable(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.hfscr |= HFSCR_TM;
+
+	return RESUME_GUEST;
+}
+
 static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 				 struct task_struct *tsk)
 {
@@ -1654,6 +1661,8 @@ XXX benchmark guest exits
 				r = kvmppc_pmu_unavailable(vcpu);
 			if (cause == FSCR_EBB_LG)
 				r = kvmppc_ebb_unavailable(vcpu);
+			if (cause == FSCR_TM_LG)
+				r = kvmppc_tm_unavailable(vcpu);
 		}
 		if (r == EMULATE_FAIL) {
 			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
@@ -1775,6 +1784,8 @@ static int kvmppc_handle_nested_exit(struct kvm_vcpu *vcpu)
 			r = kvmppc_pmu_unavailable(vcpu);
 		if (cause == FSCR_EBB_LG && (vcpu->arch.nested_hfscr & HFSCR_EBB))
 			r = kvmppc_ebb_unavailable(vcpu);
+		if (cause == FSCR_TM_LG && (vcpu->arch.nested_hfscr & HFSCR_TM))
+			r = kvmppc_tm_unavailable(vcpu);
 
 		if (r == EMULATE_FAIL)
 			r = RESUME_HOST;
@@ -3737,8 +3748,9 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu *vcpu, u64 time_limit, uns
 		msr |= MSR_VEC;
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr |= MSR_VSX;
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+			(vcpu->arch.hfscr & HFSCR_TM))
 		msr |= MSR_TM;
 	msr = msr_check_and_set(msr);
 
@@ -4453,8 +4465,9 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
 		msr |= MSR_VEC;
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr |= MSR_VSX;
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+			(vcpu->arch.hfscr & HFSCR_TM))
 		msr |= MSR_TM;
 	msr = msr_check_and_set(msr);
 
diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index ee8668f056f9..5a534f7924f2 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -168,7 +168,7 @@ static void sanitise_hv_regs(struct kvm_vcpu *vcpu, struct hv_guest_state *hr)
 	 * but preserve the interrupt cause field and facilities that might
 	 * be disabled for demand faulting in the L1.
 	 */
-	hr->hfscr &= (HFSCR_INTR_CAUSE | HFSCR_PM | HFSCR_EBB |
+	hr->hfscr &= (HFSCR_INTR_CAUSE | HFSCR_PM | HFSCR_TM | HFSCR_EBB |
 			vcpu->arch.hfscr);
 
 	/* Don't let data address watchpoint match in hypervisor state */
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index cf41261daa97..653f2765a399 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -284,8 +284,9 @@ static void store_spr_state(struct kvm_vcpu *vcpu)
 void load_vcpu_state(struct kvm_vcpu *vcpu,
 			   struct p9_host_os_sprs *host_os_sprs)
 {
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) {
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+		       (vcpu->arch.hfscr & HFSCR_TM)) {
 		unsigned long msr = vcpu->arch.shregs.msr;
 		if (MSR_TM_ACTIVE(msr)) {
 			kvmppc_restore_tm_hv(vcpu, msr, true);
@@ -316,8 +317,9 @@ void store_vcpu_state(struct kvm_vcpu *vcpu)
 #endif
 	vcpu->arch.vrsave = mfspr(SPRN_VRSAVE);
 
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) {
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+		       (vcpu->arch.hfscr & HFSCR_TM)) {
 		unsigned long msr = vcpu->arch.shregs.msr;
 		if (MSR_TM_ACTIVE(msr)) {
 			kvmppc_save_tm_hv(vcpu, msr, true);
@@ -326,6 +328,9 @@ void store_vcpu_state(struct kvm_vcpu *vcpu)
 			vcpu->arch.tfhar = mfspr(SPRN_TFHAR);
 			vcpu->arch.tfiar = mfspr(SPRN_TFIAR);
 		}
+		vcpu->arch.load_tm++; /* see load_ebb comment for details */
+		if (!vcpu->arch.load_tm)
+			vcpu->arch.hfscr &= ~HFSCR_TM;
 	}
 }
 EXPORT_SYMBOL_GPL(store_vcpu_state);
@@ -615,8 +620,9 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 		msr |= MSR_VEC;
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr |= MSR_VSX;
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+			(vcpu->arch.hfscr & HFSCR_TM))
 		msr |= MSR_TM;
 	msr = msr_check_and_set(msr);
 	/* Save MSR for restore. This is after hard disable, so EE is clear. */
-- 
2.23.0




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