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>

1 files changed, 21 insertions, 24 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 4105e1ea8dda..bec71e902be3 100644
--- 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)