linux-kernel - [PATCH 5.4 225/309] KVM: s390: do not clobber registers during guest reset/store status

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Date:   Mon, 10 Feb 2020 04:33:01 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable@...nel.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Janosch Frank <frankja@...ux.ibm.com>
Subject: [PATCH 5.4 225/309] KVM: s390: do not clobber registers during guest reset/store status

From: Christian Borntraeger <borntraeger@...ibm.com>

commit 55680890ea78be0df5e1384989f1be835043c084 upstream.

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@...nel.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@...ibm.com>
Reviewed-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Janosch Frank <frankja@...ux.ibm.com>
Link: https://lore.kernel.org/r/20200131100205.74720-2-frankja@linux.ibm.com
Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/s390/kvm/kvm-s390.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2863,9 +2863,7 @@ static void kvm_s390_vcpu_initial_reset(
 	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;
@@ -4354,7 +4352,7 @@ long kvm_arch_vcpu_ioctl(struct file *fi
 	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: {