[PATCH v3 1/2] KVM: s390: fix access register usage in ioctls

[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).
Since this routine saves the current registers to vcpu->run,
this routine erroneously saves host registers into the guest space.

Introduce a boolean in the kvm_vcpu_arch struct to indicate whether
the registers contain guest contents. If they do (the instruction
intercept path), the save can be performed and the AR translation
is done just as it is today. If they don't (the MEM_OP path), the
AR can be read from vcpu->run without stashing the current contents.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 arch/s390/include/asm/kvm_host.h | 1 +
 arch/s390/kvm/gaccess.c          | 3 ++-
 arch/s390/kvm/kvm-s390.c         | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

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..b4c805092021 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -391,7 +391,8 @@ static int ar_translation(struct kvm_vcpu *vcpu, union asce *asce, u8 ar,
 	if (ar >= NUM_ACRS)
 		return -EINVAL;
 
-	save_access_regs(vcpu->run->s.regs.acrs);
+	if (vcpu->arch.acrs_loaded)
+		save_access_regs(vcpu->run->s.regs.acrs);
 	alet.val = vcpu->run->s.regs.acrs[ar];
 
 	if (ar == 0 || alet.val == 0) {
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index ea63ac769889..61092f0e0a66 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;
-- 
2.40.1