KVM: PPC: Book3S HV P9: Demand fault TM facility registers

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.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-38-npiggin@gmail.com

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 7a55b19..d700441 100644 (file)
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -580,6 +580,9 @@ struct kvm_vcpu_arch {
        ulong ppr;
        u32 pspb;
        u8 load_ebb;
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+       u8 load_tm;
+#endif
        ulong fscr;
        ulong shadow_fscr;
        ulong ebbhr;

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index da29cf9..198f6d9 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1446,6 +1446,16 @@ static int kvmppc_ebb_unavailable(struct kvm_vcpu *vcpu)
        return RESUME_GUEST;
 }
 
+static int kvmppc_tm_unavailable(struct kvm_vcpu *vcpu)
+{
+       if (!(vcpu->arch.hfscr_permitted & HFSCR_TM))
+               return EMULATE_FAIL;
+
+       vcpu->arch.hfscr |= HFSCR_TM;
+
+       return RESUME_GUEST;
+}
+
 static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
                                 struct task_struct *tsk)
 {
@@ -1739,6 +1749,8 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
                                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);
@@ -2783,9 +2795,9 @@ static int kvmppc_core_vcpu_create_hv(struct kvm_vcpu *vcpu)
        vcpu->arch.hfscr_permitted = vcpu->arch.hfscr;
 
        /*
-        * PM, EBB is demand-faulted so start with it clear.
+        * PM, EBB, TM are demand-faulted so start with it clear.
         */
-       vcpu->arch.hfscr &= ~(HFSCR_PM | HFSCR_EBB);
+       vcpu->arch.hfscr &= ~(HFSCR_PM | HFSCR_EBB | HFSCR_TM);
 
        kvmppc_mmu_book3s_hv_init(vcpu);
 
@@ -3868,8 +3880,9 @@ 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);
 
@@ -4608,8 +4621,9 @@ 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_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 929a7c3..8499e8a 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -310,7 +310,7 @@ bool load_vcpu_state(struct kvm_vcpu *vcpu,
                if (MSR_TM_ACTIVE(guest_msr)) {
                        kvmppc_restore_tm_hv(vcpu, guest_msr, true);
                        ret = true;
-               } else {
+               } else if (vcpu->arch.hfscr & HFSCR_TM) {
                        mtspr(SPRN_TEXASR, vcpu->arch.texasr);
                        mtspr(SPRN_TFHAR, vcpu->arch.tfhar);
                        mtspr(SPRN_TFIAR, vcpu->arch.tfiar);
@@ -346,10 +346,16 @@ void store_vcpu_state(struct kvm_vcpu *vcpu)
                unsigned long guest_msr = vcpu->arch.shregs.msr;
                if (MSR_TM_ACTIVE(guest_msr)) {
                        kvmppc_save_tm_hv(vcpu, guest_msr, true);
-               } else {
+               } else if (vcpu->arch.hfscr & HFSCR_TM) {
                        vcpu->arch.texasr = mfspr(SPRN_TEXASR);
                        vcpu->arch.tfhar = mfspr(SPRN_TFHAR);
                        vcpu->arch.tfiar = mfspr(SPRN_TFIAR);
+
+                       if (!vcpu->arch.nested) {
+                               vcpu->arch.load_tm++; /* see load_ebb comment */
+                               if (!vcpu->arch.load_tm)
+                                       vcpu->arch.hfscr &= ~HFSCR_TM;
+                       }
                }
        }
 #endif
@@ -641,8 +647,9 @@ 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. */