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@xxxxxxxxxx>
Reviewed-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
arch/s390/kvm/kvm-s390.c | 45 +++++++++++++++++++++------------------------
1 file changed, 21 insertions(+), 24 deletions(-)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 4105e1e..bec71e9 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)
--
2.5.5
--
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