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    Subject[PATCH 4.14 136/173] KVM: s390: do not clobber registers during guest reset/store status
    Date
    From: Christian Borntraeger <borntraeger@de.ibm.com>

    [ Upstream commit 55680890ea78be0df5e1384989f1be835043c084 ]

    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>
    Link: https://lore.kernel.org/r/20200131100205.74720-2-frankja@linux.ibm.com
    Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 91c24e87fe10a..46fee3f4dedda 100644
    --- a/arch/s390/kvm/kvm-s390.c
    +++ b/arch/s390/kvm/kvm-s390.c
    @@ -2384,9 +2384,7 @@ static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
    memset(vcpu->arch.sie_block->gcr, 0, 16 * sizeof(__u64));
    vcpu->arch.sie_block->gcr[0] = 0xE0UL;
    vcpu->arch.sie_block->gcr[14] = 0xC2000000UL;
    - /* 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;
    @@ -3753,7 +3751,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
    }
    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: {
    --
    2.20.1


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