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 9977e886cbbc7 ("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: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 4105e1e..bec71e9 100644 (file)
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -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)