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Commit e1788bb9 authored by Christian Borntraeger's avatar Christian Borntraeger
Browse files

KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load 



Right now we switch the host fprs/vrs in kvm_arch_vcpu_load and switch
back in kvm_arch_vcpu_put. This process is already optimized
since commit 9977e886 ("s390/kernel: lazy restore fpu registers")
avoiding double save/restores on schedule. We still reload the pointers
and test the guest fpc on each context switch, though.

We can minimize the cost of vcpu_load/put by doing the test in the
VCPU_RUN ioctl itself. As most VCPU threads almost never exit to
userspace in the common fast path, this allows to avoid this overhead
for the common case (eventfd driven I/O, all exits including sleep
handled in the kernel) - making kvm_arch_vcpu_load/put basically
disappear in perf top.

Also adapt the fpu get/set ioctls.

Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: default avatarCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
parent 31d8b8d4

arch/s390/kvm/kvm-s390.c

+21 −24
Original line number Diff line number Diff line
@@ -1812,19 +1812,6 @@ __u64 kvm_s390_get_cpu_timer(struct kvm_vcpu *vcpu) 


void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)

{

	/* Save host register state */

	save_fpu_regs();

	vcpu->arch.host_fpregs.fpc = current->thread.fpu.fpc;

	vcpu->arch.host_fpregs.regs = current->thread.fpu.regs;



	if (MACHINE_HAS_VX)

		current->thread.fpu.regs = vcpu->run->s.regs.vrs;

	else

		current->thread.fpu.regs = vcpu->run->s.regs.fprs;

	current->thread.fpu.fpc = vcpu->run->s.regs.fpc;

	if (test_fp_ctl(current->thread.fpu.fpc))

		/* User space provided an invalid FPC, let's clear it */

		current->thread.fpu.fpc = 0;



	gmap_enable(vcpu->arch.enabled_gmap);

	atomic_or(CPUSTAT_RUNNING, &vcpu->arch.sie_block->cpuflags);
@@ -1842,13 +1829,6 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) 
	vcpu->arch.enabled_gmap = gmap_get_enabled();

	gmap_disable(vcpu->arch.enabled_gmap);



	/* Save guest register state */

	save_fpu_regs();

	vcpu->run->s.regs.fpc = current->thread.fpu.fpc;



	/* Restore host register state */

	current->thread.fpu.fpc = vcpu->arch.host_fpregs.fpc;

	current->thread.fpu.regs = vcpu->arch.host_fpregs.regs;

}



static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
@@ -2251,11 +2231,9 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu, 


int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)

{

	/* make sure the new values will be lazily loaded */

	save_fpu_regs();

	if (test_fp_ctl(fpu->fpc))

		return -EINVAL;

	current->thread.fpu.fpc = fpu->fpc;

	vcpu->run->s.regs.fpc = fpu->fpc;

	if (MACHINE_HAS_VX)

		convert_fp_to_vx((__vector128 *) vcpu->run->s.regs.vrs,

				 (freg_t *) fpu->fprs);
@@ -2273,7 +2251,7 @@ int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu) 
				 (__vector128 *) vcpu->run->s.regs.vrs);

	else

		memcpy(fpu->fprs, vcpu->run->s.regs.fprs, sizeof(fpu->fprs));

	fpu->fpc = current->thread.fpu.fpc;

	fpu->fpc = vcpu->run->s.regs.fpc;

	return 0;

}
@@ -2736,6 +2714,18 @@ static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) 
	}

	save_access_regs(vcpu->arch.host_acrs);

	restore_access_regs(vcpu->run->s.regs.acrs);

	/* save host (userspace) fprs/vrs */

	save_fpu_regs();

	vcpu->arch.host_fpregs.fpc = current->thread.fpu.fpc;

	vcpu->arch.host_fpregs.regs = current->thread.fpu.regs;

	if (MACHINE_HAS_VX)

		current->thread.fpu.regs = vcpu->run->s.regs.vrs;

	else

		current->thread.fpu.regs = vcpu->run->s.regs.fprs;

	current->thread.fpu.fpc = vcpu->run->s.regs.fpc;

	if (test_fp_ctl(current->thread.fpu.fpc))

		/* User space provided an invalid FPC, let's clear it */

		current->thread.fpu.fpc = 0;



	kvm_run->kvm_dirty_regs = 0;

}
@@ -2756,6 +2746,13 @@ static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) 
	kvm_run->s.regs.pfc = vcpu->arch.pfault_compare;

	save_access_regs(vcpu->run->s.regs.acrs);

	restore_access_regs(vcpu->arch.host_acrs);

	/* Save guest register state */

	save_fpu_regs();

	vcpu->run->s.regs.fpc = current->thread.fpu.fpc;

	/* Restore will be done lazily at return */

	current->thread.fpu.fpc = vcpu->arch.host_fpregs.fpc;

	current->thread.fpu.regs = vcpu->arch.host_fpregs.regs;



}



int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)