Commit a3e18ca8 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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KVM: PPC: Book3S HV P9: Demand fault EBB facility registers 



Use HFSCR facility disabling to implement demand faulting for EBB, 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: default avatarNicholas Piggin <npiggin@gmail.com>
Reviewed-by: default avatarFabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-37-npiggin@gmail.com
parent 34e02d55

arch/powerpc/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -579,6 +579,7 @@ struct kvm_vcpu_arch { 
	ulong cfar;

	ulong ppr;

	u32 pspb;

	u8 load_ebb;

	ulong fscr;

	ulong shadow_fscr;

	ulong ebbhr;

arch/powerpc/kvm/book3s_hv.c

+14 −2
Original line number Diff line number Diff line
@@ -1436,6 +1436,16 @@ static int kvmppc_pmu_unavailable(struct kvm_vcpu *vcpu) 
	return RESUME_GUEST;

}



static int kvmppc_ebb_unavailable(struct kvm_vcpu *vcpu)

{

	if (!(vcpu->arch.hfscr_permitted & HFSCR_EBB))

		return EMULATE_FAIL;



	vcpu->arch.hfscr |= HFSCR_EBB;



	return RESUME_GUEST;

}



static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,

				 struct task_struct *tsk)

{
@@ -1727,6 +1737,8 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu, 
				r = kvmppc_emulate_doorbell_instr(vcpu);

			if (cause == FSCR_PM_LG)

				r = kvmppc_pmu_unavailable(vcpu);

			if (cause == FSCR_EBB_LG)

				r = kvmppc_ebb_unavailable(vcpu);

		}

		if (r == EMULATE_FAIL) {

			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
@@ -2771,9 +2783,9 @@ static int kvmppc_core_vcpu_create_hv(struct kvm_vcpu *vcpu) 
	vcpu->arch.hfscr_permitted = vcpu->arch.hfscr;



	/*

	 * PM is demand-faulted so start with it clear.

	 * PM, EBB is demand-faulted so start with it clear.

	 */

	vcpu->arch.hfscr &= ~HFSCR_PM;

	vcpu->arch.hfscr &= ~(HFSCR_PM | HFSCR_EBB);



	kvmppc_mmu_book3s_hv_init(vcpu);

arch/powerpc/kvm/book3s_hv_p9_entry.c

+22 −6
Original line number Diff line number Diff line
@@ -232,9 +232,12 @@ static void load_spr_state(struct kvm_vcpu *vcpu, 
				struct p9_host_os_sprs *host_os_sprs)

{

	mtspr(SPRN_TAR, vcpu->arch.tar);



	if (vcpu->arch.hfscr & HFSCR_EBB) {

		mtspr(SPRN_EBBHR, vcpu->arch.ebbhr);

		mtspr(SPRN_EBBRR, vcpu->arch.ebbrr);

		mtspr(SPRN_BESCR, vcpu->arch.bescr);

	}



	if (cpu_has_feature(CPU_FTR_P9_TIDR))

		mtspr(SPRN_TIDR, vcpu->arch.tid);
@@ -265,9 +268,22 @@ static void load_spr_state(struct kvm_vcpu *vcpu, 
static void store_spr_state(struct kvm_vcpu *vcpu)

{

	vcpu->arch.tar = mfspr(SPRN_TAR);



	if (vcpu->arch.hfscr & HFSCR_EBB) {

		vcpu->arch.ebbhr = mfspr(SPRN_EBBHR);

		vcpu->arch.ebbrr = mfspr(SPRN_EBBRR);

		vcpu->arch.bescr = mfspr(SPRN_BESCR);

		/*

		 * This is like load_fp in context switching, turn off the

		 * facility after it wraps the u8 to try avoiding saving

		 * and restoring the registers each partition switch.

		 */

		if (!vcpu->arch.nested) {

			vcpu->arch.load_ebb++;

			if (!vcpu->arch.load_ebb)

				vcpu->arch.hfscr &= ~HFSCR_EBB;

		}

	}



	if (cpu_has_feature(CPU_FTR_P9_TIDR))

		vcpu->arch.tid = mfspr(SPRN_TIDR);