s390/fpu: always enable the vector facility if it is available

If the kernel detects that the s390 hardware supports the vector
facility, it is enabled by default at an early stage.  To force
it off, use the novx kernel parameter.  Note that there is a small
time window, where the vector facility is enabled before it is
forced to be off.

With enabling the vector facility by default, the FPU save and
restore functions can be improved.  They do not longer require
to manage expensive control register updates to enable or disable
the vector enablement control for particular processes.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 0 insertions, 6 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 0a67c40eece9..c6b4063fce29 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1292,7 +1292,6 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 static inline void save_fpu_to(struct fpu *dst)
 {
         dst->fpc = current->thread.fpu.fpc;
-        dst->flags = current->thread.fpu.flags;
         dst->regs = current->thread.fpu.regs;
 }
 
@@ -1303,7 +1302,6 @@ static inline void save_fpu_to(struct fpu *dst)
 static inline void load_fpu_from(struct fpu *from)
 {
         current->thread.fpu.fpc = from->fpc;
-        current->thread.fpu.flags = from->flags;
         current->thread.fpu.regs = from->regs;
 }
 
@@ -1315,15 +1313,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
         if (test_kvm_facility(vcpu->kvm, 129)) {
                 current->thread.fpu.fpc = vcpu->run->s.regs.fpc;
-                current->thread.fpu.flags = FPU_USE_VX;
                 /*
                  * Use the register save area in the SIE-control block
                  * for register restore and save in kvm_arch_vcpu_put()
                  */
                 current->thread.fpu.vxrs =
                         (__vector128 *)&vcpu->run->s.regs.vrs;
-                /* Always enable the vector extension for KVM */
-                __ctl_set_vx();
         } else
                 load_fpu_from(&vcpu->arch.guest_fpregs);
 
@@ -2326,7 +2321,6 @@ int kvm_s390_vcpu_store_status(struct kvm_vcpu *vcpu, unsigned long addr)
                  * registers and the FPC value and store them in the
                  * guest_fpregs structure.
                  */
-                WARN_ON(!is_vx_task(current));    /* XXX remove later */
                 vcpu->arch.guest_fpregs.fpc = current->thread.fpu.fpc;
                 convert_vx_to_fp(vcpu->arch.guest_fpregs.fprs,
                                  current->thread.fpu.vxrs);