Subject: [PATCH v3 44/52] KVM: PPC: Book3S HV P9: Improve mfmsr performance on entry

From: Nicholas Piggin <[email-masked]>
Date: Tue, 5 Oct 2021 02:00:41 +1000

Rearrange the MSR saving on entry so it does not follow the mtmsrd to
disable interrupts, avoiding a possible RAW scoreboard stall.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/include/asm/kvm_book3s_64.h |  2 +
 arch/powerpc/kvm/book3s_hv.c             | 18 ++-----
 arch/powerpc/kvm/book3s_hv_p9_entry.c    | 66 +++++++++++++++---------
 3 files changed, 47 insertions(+), 39 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index 0a319ed9c2fd..96f0fda50a07 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -154,6 +154,8 @@ static inline bool kvmhv_vcpu_is_radix(struct kvm_vcpu *vcpu)
 	return radix;
 }
 
+unsigned long kvmppc_msr_hard_disable_set_facilities(struct kvm_vcpu *vcpu, unsigned long msr);
+
 int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpcr, u64 *tb);
 
 #define KVM_DEFAULT_HPT_ORDER	24	/* 16MB HPT by default */
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 342b4f125d03..0bbef4587f41 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3878,6 +3878,8 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu *vcpu, u64 time_limit, uns
 	s64 dec;
 	int trap;
 
+	msr = mfmsr();
+
 	save_p9_host_os_sprs(&host_os_sprs);
 
 	/*
@@ -3888,24 +3890,10 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu *vcpu, u64 time_limit, uns
 	 */
 	host_psscr = mfspr(SPRN_PSSCR_PR);
 
-	hard_irq_disable();
+	kvmppc_msr_hard_disable_set_facilities(vcpu, msr);
 	if (lazy_irq_pending())
 		return 0;
 
-	/* MSR bits may have been cleared by context switch */
-	msr = 0;
-	if (IS_ENABLED(CONFIG_PPC_FPU))
-		msr |= MSR_FP;
-	if (cpu_has_feature(CPU_FTR_ALTIVEC))
-		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)) &&
-			(vcpu->arch.hfscr & HFSCR_TM))
-		msr |= MSR_TM;
-	msr = msr_check_and_set(msr);
-
 	if (unlikely(load_vcpu_state(vcpu, &host_os_sprs)))
 		msr = mfmsr(); /* TM restore can update msr */
 
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index a45ba584c734..646f487ebf97 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -632,6 +632,44 @@ static void save_clear_guest_mmu(struct kvm *kvm, struct kvm_vcpu *vcpu)
 	}
 }
 
+unsigned long kvmppc_msr_hard_disable_set_facilities(struct kvm_vcpu *vcpu, unsigned long msr)
+{
+	unsigned long msr_needed = 0;
+
+	msr &= ~MSR_EE;
+
+	/* MSR bits may have been cleared by context switch so must recheck */
+	if (IS_ENABLED(CONFIG_PPC_FPU))
+		msr_needed |= MSR_FP;
+	if (cpu_has_feature(CPU_FTR_ALTIVEC))
+		msr_needed |= MSR_VEC;
+	if (cpu_has_feature(CPU_FTR_VSX))
+		msr_needed |= MSR_VSX;
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+			(vcpu->arch.hfscr & HFSCR_TM))
+		msr_needed |= MSR_TM;
+
+	/*
+	 * This could be combined with MSR[RI] clearing, but that expands
+	 * the unrecoverable window. It would be better to cover unrecoverable
+	 * with KVM bad interrupt handling rather than use MSR[RI] at all.
+	 *
+	 * Much more difficult and less worthwhile to combine with IR/DR
+	 * disable.
+	 */
+	if ((msr & msr_needed) != msr_needed) {
+		msr |= msr_needed;
+		__mtmsrd(msr, 0);
+	} else {
+		__hard_irq_disable();
+	}
+	local_paca->irq_happened |= PACA_IRQ_HARD_DIS;
+
+	return msr;
+}
+EXPORT_SYMBOL_GPL(kvmppc_msr_hard_disable_set_facilities);
+
 int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpcr, u64 *tb)
 {
 	struct p9_host_os_sprs host_os_sprs;
@@ -665,6 +703,9 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	vcpu->arch.ceded = 0;
 
+	/* Save MSR for restore, with EE clear. */
+	msr = mfmsr() & ~MSR_EE;
+
 	host_hfscr = mfspr(SPRN_HFSCR);
 	host_ciabr = mfspr(SPRN_CIABR);
 	host_psscr = mfspr(SPRN_PSSCR_PR);
@@ -686,35 +727,12 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	save_p9_host_os_sprs(&host_os_sprs);
 
-	/*
-	 * This could be combined with MSR[RI] clearing, but that expands
-	 * the unrecoverable window. It would be better to cover unrecoverable
-	 * with KVM bad interrupt handling rather than use MSR[RI] at all.
-	 *
-	 * Much more difficult and less worthwhile to combine with IR/DR
-	 * disable.
-	 */
-	hard_irq_disable();
+	msr = kvmppc_msr_hard_disable_set_facilities(vcpu, msr);
 	if (lazy_irq_pending()) {
 		trap = 0;
 		goto out;
 	}
 
-	/* MSR bits may have been cleared by context switch */
-	msr = 0;
-	if (IS_ENABLED(CONFIG_PPC_FPU))
-		msr |= MSR_FP;
-	if (cpu_has_feature(CPU_FTR_ALTIVEC))
-		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)) &&
-			(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. */
-
 	if (unlikely(load_vcpu_state(vcpu, &host_os_sprs)))
 		msr = mfmsr(); /* MSR may have been updated */
 
-- 
2.23.0