[PATCH v2 1/2] KVM: s390: load guest access registers in MEM_OP ioctl

[Eric Farman <farman@linux.ibm.com>]

The routine ar_translation() can be reached by both the instruction
intercept path (where the access registers had been loaded with the
guest register contents), and the MEM_OP ioctls (which hadn't).
This latter case means that any ALET the guest expects to be used
would be ignored.

Fix this by swapping the host/guest access registers around the
MEM_OP ioctl, in the same way that the KVM_RUN ioctl does with
sync_regs()/store_regs(). The full register swap isn't needed here,
since only the access registers are used in this interface.

Introduce a boolean in the kvm_vcpu_arch struct to indicate the
guest ARs have been loaded into the registers. This permits a
warning to be emitted if entering this path without a proper
register setup.

Suggested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 arch/s390/include/asm/kvm_host.h |  1 +
 arch/s390/kvm/gaccess.c          |  2 ++
 arch/s390/kvm/kvm-s390.c         | 11 +++++++++++
 3 files changed, 14 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 52664105a473..c86215eb4ca7 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -765,6 +765,7 @@ struct kvm_vcpu_arch {
 	__u64 cputm_start;
 	bool gs_enabled;
 	bool skey_enabled;
+	bool acrs_loaded;
 	struct kvm_s390_pv_vcpu pv;
 	union diag318_info diag318_info;
 };
diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 5bfcc50c1a68..33587bb4c9e8 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -391,6 +391,8 @@ static int ar_translation(struct kvm_vcpu *vcpu, union asce *asce, u8 ar,
 	if (ar >= NUM_ACRS)
 		return -EINVAL;
 
+	WARN_ON_ONCE(!vcpu->arch.acrs_loaded);
+
 	save_access_regs(vcpu->run->s.regs.acrs);
 	alet.val = vcpu->run->s.regs.acrs[ar];
 
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index ea63ac769889..c60ec561f7f1 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3951,6 +3951,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 				    KVM_SYNC_ARCH0 |
 				    KVM_SYNC_PFAULT |
 				    KVM_SYNC_DIAG318;
+	vcpu->arch.acrs_loaded = false;
 	kvm_s390_set_prefix(vcpu, 0);
 	if (test_kvm_facility(vcpu->kvm, 64))
 		vcpu->run->kvm_valid_regs |= KVM_SYNC_RICCB;
@@ -4951,6 +4952,7 @@ static void sync_regs(struct kvm_vcpu *vcpu)
 	}
 	save_access_regs(vcpu->arch.host_acrs);
 	restore_access_regs(vcpu->run->s.regs.acrs);
+	vcpu->arch.acrs_loaded = true;
 	/* save host (userspace) fprs/vrs */
 	save_fpu_regs();
 	vcpu->arch.host_fpregs.fpc = current->thread.fpu.fpc;
@@ -5021,6 +5023,7 @@ static void store_regs(struct kvm_vcpu *vcpu)
 	kvm_run->s.regs.pfc = vcpu->arch.pfault_compare;
 	save_access_regs(vcpu->run->s.regs.acrs);
 	restore_access_regs(vcpu->arch.host_acrs);
+	vcpu->arch.acrs_loaded = false;
 	/* Save guest register state */
 	save_fpu_regs();
 	vcpu->run->s.regs.fpc = current->thread.fpu.fpc;
@@ -5391,6 +5394,11 @@ static long kvm_s390_vcpu_mem_op(struct kvm_vcpu *vcpu,
 			return -ENOMEM;
 	}
 
+	/* Swap host/guest access registers */
+	save_access_regs(vcpu->arch.host_acrs);
+	restore_access_regs(vcpu->run->s.regs.acrs);
+	vcpu->arch.acrs_loaded = true;
+
 	acc_mode = mop->op == KVM_S390_MEMOP_LOGICAL_READ ? GACC_FETCH : GACC_STORE;
 	if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
 		r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size,
@@ -5420,6 +5428,9 @@ static long kvm_s390_vcpu_mem_op(struct kvm_vcpu *vcpu,
 		kvm_s390_inject_prog_irq(vcpu, &vcpu->arch.pgm);
 
 out_free:
+	save_access_regs(vcpu->run->s.regs.acrs);
+	restore_access_regs(vcpu->arch.host_acrs);
+	vcpu->arch.acrs_loaded = false;
 	vfree(tmpbuf);
 	return r;
 }
-- 
2.40.1