Re: [PATCH v10 1/6] KVM: s390: do not clobber registers during guest reset/store status

Christian Borntraeger
2020-01-31T11:24:56Z

On 31.01.20 11:02, Janosch Frank wrote:
> From: Christian Borntraeger <borntraeger@de.ibm.com>
>
> The initial CPU reset clobbers the userspace fpc and the store status
> ioctl clobbers the guest acrs + fpr. As these calls are only done via
> ioctl (and not via vcpu_run), no CPU context is loaded, so we can (and
> must) act directly on the sync regs, not on the thread context.
>
> Cc: stable@kernel.org
> Fixes: e1788bb995be ("KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load")
> Fixes: 31d8b8d41a7e ("KVM: s390: handle access registers in the run ioctl not in vcpu_put/load")
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

Thanks applied.

> ---
> arch/s390/kvm/kvm-s390.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index d9e6bf3d54f0..876802894b35 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2860,9 +2860,7 @@ static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
> vcpu->arch.sie_block->gcr[14] = CR14_UNUSED_32 |
> CR14_UNUSED_33 |
> CR14_EXTERNAL_DAMAGE_SUBMASK;
> - /* make sure the new fpc will be lazily loaded */
> - save_fpu_regs();
> - current->thread.fpu.fpc = 0;
> + vcpu->run->s.regs.fpc = 0;
> vcpu->arch.sie_block->gbea = 1;
> vcpu->arch.sie_block->pp = 0;
> vcpu->arch.sie_block->fpf &= ~FPF_BPBC;
> @@ -4351,7 +4349,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> switch (ioctl) {
> case KVM_S390_STORE_STATUS:
> idx = srcu_read_lock(&vcpu->kvm->srcu);
> - r = kvm_s390_vcpu_store_status(vcpu, arg);
> + r = kvm_s390_store_status_unloaded(vcpu, arg);
> srcu_read_unlock(&vcpu->kvm->srcu, idx);
> break;
> case KVM_S390_SET_INITIAL_PSW: {
>