[PATCH v4 00/13] KVM: s390: Misc fixes

[PATCH v4 00/13] KVM: s390: Misc fixes

[Claudio Imbrenda]

Fix a bunch of small issues that came up during the previous round of fixes.

They are mostly extremely unlikely races, but they should be fixed
nonetheless.

v3->v4
* Improve patch descriptions, add comments
* Use smp_store_release and smp_load_acquire in the first patch
* Multiple fixes in patch 4: potential NULL pointer dereference,
  incorrect behaviour in low memory condition
* Rework patch 8 to use scope-based cleanup instead of gotos.
* Three new patches:
  - KVM: s390: Fix kvm_arch_commit_memory_region() when low on memory
  - KVM: s390: Fix kvm_s390_vcpu_unsetup_cmma()
  - KVM: s390: Fix sca_clear_ext_call() for UCONTROL

v2->v3
* Use READ_ONCE to pair with WRITE_ONCE in the first patch
* Fix leaking PGM_ADDRESSING also in kvm_s390_keyop() and related functions
* Fix and improve commit messages
* Use slots_arch_lock instead of slots_lock for ESSA operations
* Use normal spin_{,un}lock() functions instead of scoped_guard to avoid
  mixing the two styles
* Use the newly introduced vcpu->arch.initialized to determine whether the
  SCA entry needs to be cleared
* Improve handling of -EINTR; handle_mvpg_pei() needed some refactoring to
  deal with it properly
* Three new patches:
  - Free the mmu cache when kvm_arch_vcpu_create() fails
  - Fix ordering when adding to SCA
  - Fix cleanup in kvm_s390_pv_create_cpu()

v1->v2
* Drop some patches that have been picked upstream in the meantime.
* Drop patch 3, as it was trying to fix a bug that does not exist
* Avoid the NULL gmap dereference by using a flag
* Fix the return value of kvm_s390_[gp]et_skeys too
* Use kvm->slots_arch_lock instead of kvm->slots_lock for CMMA and ESSA
  handling, to avoid potential deadlocks with the RCU.
* Three new patches to fix other issues that came out while fixing the
  other issues

Claudio Imbrenda (13):
  KVM: s390: Fix unlikely NULL gmap dereference
  KVM: s390: Fix leaking of PGM_ADDRESSING to userspace
  KVM: s390: Fix race in __do_essa()
  KVM: s390: cmma: Fix dirty tracking when removing memslot
  KVM: s390: ucontrol: Add missing locking around gmap_remove_child()
  KVM: s390: Fix overclearing ESCA in case of error
  KVM: s390: Return -EINTR if a signal was pending while faulting-in
  KVM: s390: Free the mmu cache when kvm_arch_vcpu_create() fails
  KVM: s390: Fix ordering when adding to SCA
  KVM: s390: Fix cleanup in kvm_s390_pv_create_cpu()
  KVM: s390: Fix kvm_arch_commit_memory_region() when low on memory
  KVM: s390: Fix kvm_s390_vcpu_unsetup_cmma()
  KVM: s390: Fix sca_clear_ext_call() for UCONTROL

 arch/s390/include/asm/kvm_host.h |   1 +
 arch/s390/kvm/dat.c              |  23 ++++--
 arch/s390/kvm/dat.h              |   2 +-
 arch/s390/kvm/faultin.c          |   4 +-
 arch/s390/kvm/intercept.c        |  23 +++---
 arch/s390/kvm/interrupt.c        |   7 +-
 arch/s390/kvm/kvm-s390.c         | 121 +++++++++++++++++++------------
 arch/s390/kvm/priv.c             |  10 ++-
 arch/s390/kvm/pv.c               |  43 +++++------
 9 files changed, 141 insertions(+), 93 deletions(-)

-- 
2.55.0

[PATCH v4 01/13] KVM: s390: Fix unlikely NULL gmap dereference

[Claudio Imbrenda]

When creating a new vCPU, kvm_vm_ioctl_create_vcpu() will call
kvm_arch_vcpu_postcreate() after the file descriptor for the new vCPU
has been created. The new file descriptor has not been returned yet,
but a malicious userspace program could try to guess it.

If a malicious userspace program manages to start the newly created vCPU
before kvm_arch_vcpu_postcreate() is called, __vcpu_run() will try to
dereference vcpu->arch.gmap and trigger a NULL pointer dereference.

Fix this by adding a new field to struct kvm_vcpu_arch to keep track of
the initialization status of the vCPU. Refuse to run a vCPU that is not
fully initialized.

Fixes: dafd032a15f8 ("KVM: s390: move vcpu specific initalization to a later point")
Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
---
 arch/s390/include/asm/kvm_host.h |  1 +
 arch/s390/kvm/kvm-s390.c         | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index eaa34c5bd3c1..edf75b6ad20c 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -440,6 +440,7 @@ struct kvm_vcpu_arch {
 	bool skey_enabled;
 	/* Indicator if the access registers have been loaded from guest */
 	bool acrs_loaded;
+	bool initialized;
 	struct kvm_s390_pv_vcpu pv;
 	union diag318_info diag318_info;
 	struct kvm_s390_mmu_cache *mc;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 150b5dd2170e..f86b4b0b356f 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3613,6 +3613,9 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 	if (test_kvm_facility(vcpu->kvm, 74) || vcpu->kvm->arch.user_instr0 ||
 	    vcpu->kvm->arch.user_operexec)
 		vcpu->arch.sie_block->ictl |= ICTL_OPEREXC;
+
+	/* Pairs with smp_load_acquire() in kvm_arch_vcpu_ioctl_run() and kvm_arch_vcpu_ioctl() */
+	smp_store_release(&vcpu->arch.initialized, true);
 }
 
 static bool kvm_has_pckmo_subfunc(struct kvm *kvm, unsigned long nr)
@@ -5039,6 +5042,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 	    kvm_run->kvm_dirty_regs & ~KVM_SYNC_S390_VALID_FIELDS)
 		return -EINVAL;
 
+	/* Pairs with smp_store_release() in kvm_arch_vcpu_postcreate() */
+	if (!smp_load_acquire(&vcpu->arch.initialized))
+		return -EINVAL;
+
 	vcpu_load(vcpu);
 
 	if (guestdbg_exit_pending(vcpu)) {
@@ -5523,6 +5530,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	long r;
 	u16 rc, rrc;
 
+	/* Pairs with smp_store_release() in kvm_arch_vcpu_postcreate() */
+	if (!smp_load_acquire(&vcpu->arch.initialized))
+		return -EINVAL;
+
 	vcpu_load(vcpu);
 
 	switch (ioctl) {
-- 
2.55.0

Re: [PATCH v4 01/13] KVM: s390: Fix unlikely NULL gmap dereference

[Christian Borntraeger]

Am 28.07.26 um 19:06 schrieb Claudio Imbrenda:
> When creating a new vCPU, kvm_vm_ioctl_create_vcpu() will call
> kvm_arch_vcpu_postcreate() after the file descriptor for the new vCPU
> has been created. The new file descriptor has not been returned yet,
> but a malicious userspace program could try to guess it.
> 
> If a malicious userspace program manages to start the newly created vCPU
> before kvm_arch_vcpu_postcreate() is called, __vcpu_run() will try to
> dereference vcpu->arch.gmap and trigger a NULL pointer dereference.
> 
> Fix this by adding a new field to struct kvm_vcpu_arch to keep track of
> the initialization status of the vCPU. Refuse to run a vCPU that is not
> fully initialized.
> 
> Fixes: dafd032a15f8 ("KVM: s390: move vcpu specific initalization to a later point")
> Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
> Reviewed-by: Janosch Frank <frankja@linux.ibm.com>

Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>

[PATCH v4 02/13] KVM: s390: Fix leaking of PGM_ADDRESSING to userspace

[Claudio Imbrenda]

If kvm_s390_set_cmma_bits() is asked to set CMMA values outside of a
memslot, PGM_ADDRESSING (5) is returned, instead of a negative error
value.

Same issue with kvm_s390_{g,s}et_skeys(), kvm_s390_keyop(), and
dat_reset_reference_bit().

Fix by returning -EFAULT whenever the return value would be > 0, which
is consistent with the behaviour before the gmap rewrite.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/dat.c      | 16 ++++++++++------
 arch/s390/kvm/dat.h      |  2 +-
 arch/s390/kvm/kvm-s390.c | 16 ++++++++--------
 arch/s390/kvm/priv.c     |  5 +++--
 4 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c
index ed4259d17629..171b61959908 100644
--- a/arch/s390/kvm/dat.c
+++ b/arch/s390/kvm/dat.c
@@ -755,13 +755,15 @@ int dat_cond_set_storage_key(struct kvm_s390_mmu_cache *mmc, union asce asce, gf
 	return rc;
 }
 
-int dat_reset_reference_bit(union asce asce, gfn_t gfn)
+int dat_reset_reference_bit(union asce asce, gfn_t gfn, union skey *skey)
 {
 	union pgste pgste, old;
 	union crste *crstep;
 	union pte *ptep;
 	int rc;
 
+	skey->skey = 0;
+
 	rc = dat_entry_walk(NULL, gfn, asce, DAT_WALK_ANY, TABLE_TYPE_PAGE_TABLE, &crstep, &ptep);
 	if (rc)
 		return rc;
@@ -771,21 +773,23 @@ int dat_reset_reference_bit(union asce asce, gfn_t gfn)
 
 		if (!crste.h.fc || !crste.s.fc1.pr)
 			return 0;
-		return page_reset_referenced(large_crste_to_phys(*crstep, gfn));
+		skey->skey = page_reset_referenced(large_crste_to_phys(*crstep, gfn)) << 1;
+		return 0;
 	}
 	old = pgste_get_lock(ptep);
 	pgste = old;
 
 	if (!ptep->h.i) {
-		rc = page_reset_referenced(pte_origin(*ptep));
-		pgste.hr = rc >> 1;
+		skey->skey = page_reset_referenced(pte_origin(*ptep)) << 1;
+		pgste.hr = skey->r;
 	}
-	rc |= (pgste.gr << 1) | pgste.gc;
+	skey->r |= pgste.gr;
+	skey->c |= pgste.gc;
 	pgste.gr = 0;
 
 	dat_update_ptep_sd(old, pgste, ptep);
 	pgste_set_unlock(ptep, pgste);
-	return rc;
+	return 0;
 }
 
 static long dat_reset_skeys_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct dat_walk *walk)
diff --git a/arch/s390/kvm/dat.h b/arch/s390/kvm/dat.h
index fad605305e05..141ee7b9f019 100644
--- a/arch/s390/kvm/dat.h
+++ b/arch/s390/kvm/dat.h
@@ -537,7 +537,7 @@ int dat_set_storage_key(struct kvm_s390_mmu_cache *mc, union asce asce, gfn_t gf
 			union skey skey, bool nq);
 int dat_cond_set_storage_key(struct kvm_s390_mmu_cache *mmc, union asce asce, gfn_t gfn,
 			     union skey skey, union skey *oldkey, bool nq, bool mr, bool mc);
-int dat_reset_reference_bit(union asce asce, gfn_t gfn);
+int dat_reset_reference_bit(union asce asce, gfn_t gfn, union skey *skey);
 long dat_reset_skeys(union asce asce, gfn_t start);
 
 unsigned long dat_get_ptval(struct page_table *table, struct ptval_param param);
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index f86b4b0b356f..7bc6426f5f4d 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -571,7 +571,7 @@ static int kvm_s390_keyop(struct kvm_s390_mmu_cache *mc, struct kvm *kvm, int op
 	switch (op) {
 	case KVM_S390_KEYOP_SSKE:
 		r = dat_cond_set_storage_key(mc, asce, gfn, skey, &skey, 0, 0, 0);
-		if (r >= 0)
+		if (r == 0 || r == 1)
 			return skey.skey;
 		break;
 	case KVM_S390_KEYOP_ISKE:
@@ -580,14 +580,14 @@ static int kvm_s390_keyop(struct kvm_s390_mmu_cache *mc, struct kvm *kvm, int op
 			return skey.skey;
 		break;
 	case KVM_S390_KEYOP_RRBE:
-		r = dat_reset_reference_bit(asce, gfn);
-		if (r > 0)
-			return r << 1;
+		r = dat_reset_reference_bit(asce, gfn, &skey);
+		if (!r)
+			return skey.skey;
 		break;
 	default:
 		return -EINVAL;
 	}
-	return r;
+	return r > 0 ? -EFAULT : r;
 }
 
 /* Section: device related */
@@ -2214,7 +2214,7 @@ static int kvm_s390_get_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
 	}
 
 	kvfree(keys);
-	return r;
+	return r <= 0 ? r : -EFAULT;
 }
 
 static int kvm_s390_set_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
@@ -2276,7 +2276,7 @@ static int kvm_s390_set_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
 	kvm_s390_free_mmu_cache(mc);
 out:
 	kvfree(keys);
-	return r;
+	return r <= 0 ? r : -EFAULT;
 }
 
 /*
@@ -2386,7 +2386,7 @@ static int kvm_s390_set_cmma_bits(struct kvm *kvm,
 
 	set_bit(GMAP_FLAG_USES_CMM, &kvm->arch.gmap->flags);
 
-	return r;
+	return r <= 0 ? r : -EFAULT;
 }
 
 /**
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index ad0ddc433a73..ea5a99537346 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -289,6 +289,7 @@ static int handle_iske(struct kvm_vcpu *vcpu)
 static int handle_rrbe(struct kvm_vcpu *vcpu)
 {
 	unsigned long gaddr;
+	union skey skey;
 	int reg1, reg2;
 	int rc;
 
@@ -307,12 +308,12 @@ static int handle_rrbe(struct kvm_vcpu *vcpu)
 	gaddr = kvm_s390_logical_to_effective(vcpu, gaddr);
 	gaddr = kvm_s390_real_to_abs(vcpu, gaddr);
 	scoped_guard(read_lock, &vcpu->kvm->mmu_lock)
-		rc = dat_reset_reference_bit(vcpu->arch.gmap->asce, gpa_to_gfn(gaddr));
+		rc = dat_reset_reference_bit(vcpu->arch.gmap->asce, gpa_to_gfn(gaddr), &skey);
 	if (rc > 0)
 		return kvm_s390_inject_program_int(vcpu, rc);
 	if (rc < 0)
 		return rc;
-	kvm_s390_set_psw_cc(vcpu, rc);
+	kvm_s390_set_psw_cc(vcpu, (skey.skey >> 1) & 3);
 	return 0;
 }
 
-- 
2.55.0

[PATCH v4 03/13] KVM: s390: Fix race in __do_essa()

[Claudio Imbrenda]

An unlikely race between __do_essa() and kvm_s390_vm_start_migration(),
kvm_s390_vm_stop_migration(), or dat_get_cmma() was possible.

Fix by locking kvm->slots_lock. Since this is not a hot path, the
overhead of an additional mutex is negligible.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 14 +++++++-------
 arch/s390/kvm/priv.c     |  5 +++--
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 7bc6426f5f4d..100911ee793a 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1300,7 +1300,9 @@ static int kvm_s390_vm_set_migration(struct kvm *kvm,
 {
 	int res = -ENXIO;
 
-	mutex_lock(&kvm->slots_lock);
+	guard(srcu)(&kvm->srcu);
+	guard(mutex)(&kvm->slots_arch_lock);
+
 	switch (attr->attr) {
 	case KVM_S390_VM_MIGRATION_START:
 		res = kvm_s390_vm_start_migration(kvm);
@@ -1311,7 +1313,6 @@ static int kvm_s390_vm_set_migration(struct kvm *kvm,
 	default:
 		break;
 	}
-	mutex_unlock(&kvm->slots_lock);
 
 	return res;
 }
@@ -2998,9 +2999,8 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 		r = -EFAULT;
 		if (copy_from_user(&args, argp, sizeof(args)))
 			break;
-		mutex_lock(&kvm->slots_lock);
-		r = kvm_s390_get_cmma_bits(kvm, &args);
-		mutex_unlock(&kvm->slots_lock);
+		scoped_guard(mutex, &kvm->slots_arch_lock)
+			r = kvm_s390_get_cmma_bits(kvm, &args);
 		if (!r) {
 			r = copy_to_user(argp, &args, sizeof(args));
 			if (r)
@@ -3014,9 +3014,9 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 		r = -EFAULT;
 		if (copy_from_user(&args, argp, sizeof(args)))
 			break;
-		mutex_lock(&kvm->slots_lock);
+		mutex_lock(&kvm->slots_arch_lock);
 		r = kvm_s390_set_cmma_bits(kvm, &args);
-		mutex_unlock(&kvm->slots_lock);
+		mutex_unlock(&kvm->slots_arch_lock);
 		break;
 	}
 	case KVM_S390_PV_COMMAND: {
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index ea5a99537346..b1ba24c346ef 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -1261,8 +1261,9 @@ static int handle_essa(struct kvm_vcpu *vcpu)
 		/* Retry the ESSA instruction */
 		kvm_s390_retry_instr(vcpu);
 	} else {
-		scoped_guard(read_lock, &vcpu->kvm->mmu_lock)
-			i = __do_essa(vcpu, orc);
+		scoped_guard(mutex, &vcpu->kvm->slots_arch_lock)
+			scoped_guard(read_lock, &vcpu->kvm->mmu_lock)
+				i = __do_essa(vcpu, orc);
 		if (i < 0)
 			return i;
 		/* Account for the possible extra cbrl entry */
-- 
2.55.0

[PATCH v4 04/13] KVM: s390: cmma: Fix dirty tracking when removing memslot

[Claudio Imbrenda]

When a memslot is removed, all ptes that mapped the slot are cleared or
even deallocated. If this happens while the system is in migration
mode, and if cmma-dirty pages are removed, the cmma-dirty counter will
not reflect reality.

Fix by appropriately decrementing the cmma-dirty counter when removing
a memslot.

Opportunistically improve kvm_arch_commit_memory_region() to use
__free() for the struct kvm_s390_mmu_cache.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/dat.c      |  7 ++++++-
 arch/s390/kvm/kvm-s390.c | 19 +++++++++++++++++--
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c
index 171b61959908..3f2d6e8902d7 100644
--- a/arch/s390/kvm/dat.c
+++ b/arch/s390/kvm/dat.c
@@ -850,6 +850,7 @@ static long _dat_slot_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct dat_wal
 	struct slot_priv *p = walk->priv;
 	union crste dummy = { .val = p->token };
 	union pte new_pte, pte = READ_ONCE(*ptep);
+	union pgste pgste;
 
 	new_pte = _PTE_TOK(dummy.tok.type, dummy.tok.par);
 
@@ -857,7 +858,11 @@ static long _dat_slot_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct dat_wal
 	if (pte.val == new_pte.val)
 		return 0;
 
-	dat_ptep_xchg(ptep, new_pte, gfn, walk->asce, false);
+	pgste = pgste_get_lock(ptep);
+	pgste = __dat_ptep_xchg(ptep, pgste, new_pte, gfn, walk->asce, false);
+	pgste.cmma_d = 0;
+	pgste_set_unlock(ptep, pgste);
+
 	return 0;
 }
 
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 100911ee793a..7b37e410d416 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5805,14 +5805,24 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	return 0;
 }
 
+static long cmma_d_count_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct dat_walk *walk)
+{
+	if (pgste_of(ptep)->cmma_d)
+		atomic64_dec(walk->priv);
+	return 0;
+}
+
 void kvm_arch_commit_memory_region(struct kvm *kvm,
 				struct kvm_memory_slot *old,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	struct kvm_s390_mmu_cache *mc = NULL;
+	const struct dat_walk_ops ops = { .pte_entry = cmma_d_count_pte, };
+	struct kvm_s390_mmu_cache *mc __free(kvm_s390_mmu_cache) = NULL;
 	int rc = 0;
 
+	guard(mutex)(&kvm->slots_arch_lock);
+
 	if (change == KVM_MR_FLAGS_ONLY)
 		return;
 
@@ -5823,6 +5833,12 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	}
 
 	scoped_guard(write_lock, &kvm->mmu_lock) {
+		if (kvm->arch.migration_mode && kvm->arch.use_cmma && old) {
+			_dat_walk_gfn_range(old->base_gfn, old->base_gfn + old->npages,
+					    kvm->arch.gmap->asce, &ops, DAT_WALK_IGN_HOLES,
+					    &kvm->arch.cmma_dirty_pages);
+		}
+
 		switch (change) {
 		case KVM_MR_DELETE:
 			rc = dat_delete_slot(mc, kvm->arch.gmap->asce, old->base_gfn, old->npages);
@@ -5844,7 +5860,6 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 out:
 	if (rc)
 		pr_warn("failed to commit memory region\n");
-	kvm_s390_free_mmu_cache(mc);
 	return;
 }
 
-- 
2.55.0

[PATCH v4 05/13] KVM: s390: ucontrol: Add missing locking around gmap_remove_child()

[Claudio Imbrenda]

gmap_remove_child() needs to be called while holding the children_lock
of the parent gmap. This was not the case in the error handling path of
kvm_arch_vcpu_create() for UCONTROL guests.

Fix by adding the missing lock.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 7b37e410d416..82c6c8632e1b 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3870,7 +3870,9 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 
 out_ucontrol_uninit:
 	if (kvm_is_ucontrol(vcpu->kvm)) {
+		spin_lock(&vcpu->kvm->arch.gmap->children_lock);
 		gmap_remove_child(vcpu->arch.gmap);
+		spin_unlock(&vcpu->kvm->arch.gmap->children_lock);
 		vcpu->arch.gmap = gmap_put(vcpu->arch.gmap);
 	}
 out_free_sie_block:
-- 
2.55.0

[PATCH v4 06/13] KVM: s390: Fix overclearing ESCA in case of error

[Claudio Imbrenda]

If an attempt is made to create a vCPU with an already existing ID,
the duplicated vCPU will be destroyed. When destroying a vCPU, its
ESCA entry will be cleared. In the above scenario, the spurious
duplicate vCPU is destroyed, but the ESCA entry corresponding to the
original vCPU is cleared.

Fix by skipping clearing the ESCA entry if the vCPU creation was not
successful, i.e. if the pointer to the ESCA in the state description is
not set.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
---
 arch/s390/kvm/interrupt.c | 2 +-
 arch/s390/kvm/kvm-s390.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 9e3e6b0d72ad..2acdff130fa6 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -86,7 +86,7 @@ static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
 	struct esca_block *sca = vcpu->kvm->arch.sca;
 	union esca_sigp_ctrl *sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl;
 
-	if (!kvm_s390_use_sca_entries())
+	if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized)
 		return;
 	kvm_s390_clear_cpuflags(vcpu, CPUSTAT_ECALL_PEND);
 
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 82c6c8632e1b..47eba1664bec 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3461,7 +3461,7 @@ static void sca_del_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct esca_block *sca = vcpu->kvm->arch.sca;
 
-	if (!kvm_s390_use_sca_entries())
+	if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized)
 		return;
 
 	clear_bit_inv(vcpu->vcpu_id, (unsigned long *)sca->mcn);
-- 
2.55.0

[PATCH v4 07/13] KVM: s390: Return -EINTR if a signal was pending while faulting-in

[Claudio Imbrenda]

If a signal is pending while trying to fault-in a page, return -EINTR
instead of -EAGAIN.

Also fix unpack_one() and handle_mvpg_pei() so that they can handle
-EINTR properly.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes: e907ae530133 ("KVM: s390: Add helper functions for fault handling")
---
 arch/s390/kvm/faultin.c   |  4 ++--
 arch/s390/kvm/intercept.c | 23 +++++++++++++----------
 arch/s390/kvm/pv.c        |  2 +-
 3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/arch/s390/kvm/faultin.c b/arch/s390/kvm/faultin.c
index fee80047bd94..4ff4c5970956 100644
--- a/arch/s390/kvm/faultin.c
+++ b/arch/s390/kvm/faultin.c
@@ -92,8 +92,8 @@ int kvm_s390_faultin_gfn(struct kvm_vcpu *vcpu, struct kvm *kvm, struct guest_fa
 		if (is_noslot_pfn(f->pfn))
 			return PGM_ADDRESSING;
 		/* Signal pending: try again. */
-		if (f->pfn == KVM_PFN_ERR_SIGPENDING)
-			return -EAGAIN;
+		if (is_sigpending_pfn(f->pfn))
+			return -EINTR;
 		/* Check if it's read-only memory; don't try to actually handle that case. */
 		if (f->pfn == KVM_PFN_ERR_RO_FAULT)
 			return -EOPNOTSUPP;
diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index 1980df61ef30..a40fe2a10cbf 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -369,27 +369,30 @@ static int handle_mvpg_pei(struct kvm_vcpu *vcpu)
 	if (rc)
 		return kvm_s390_inject_prog_cond(vcpu, rc);
 
-	do {
-		rc = kvm_s390_faultin_gfn_simple(vcpu, NULL, gpa_to_gfn(srcaddr), false);
-	} while (rc == -EAGAIN);
-	if (rc)
-		return rc;
-
-	/* Ensure that the source is paged-in, no actual access -> no key checking */
+	/* Ensure that the destination is paged-in, no actual access -> no key checking */
 	rc = guest_translate_address_with_key(vcpu, vcpu->run->s.regs.gprs[reg1],
 					      reg1, &dstaddr, GACC_STORE, 0);
 	if (rc)
 		return kvm_s390_inject_prog_cond(vcpu, rc);
 
+	/*
+	 * If an error happens below, the instruction needs to be retried.
+	 * Positive error codes are impossible; addressing exceptions would
+	 * have been discovered and reported above.
+	 */
+	kvm_s390_retry_instr(vcpu);
+
 	do {
-		rc = kvm_s390_faultin_gfn_simple(vcpu, NULL, gpa_to_gfn(dstaddr), true);
+		rc = kvm_s390_faultin_gfn_simple(vcpu, NULL, gpa_to_gfn(srcaddr), false);
 	} while (rc == -EAGAIN);
 	if (rc)
 		return rc;
 
-	kvm_s390_retry_instr(vcpu);
+	do {
+		rc = kvm_s390_faultin_gfn_simple(vcpu, NULL, gpa_to_gfn(dstaddr), true);
+	} while (rc == -EAGAIN);
 
-	return 0;
+	return rc;
 }
 
 static int handle_partial_execution(struct kvm_vcpu *vcpu)
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index 1beacc841ca8..dc204b521052 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -809,7 +809,7 @@ static int unpack_one(struct kvm *kvm, unsigned long addr, u64 tweak,
 			return -EAGAIN;
 	}
 
-	if (ret && ret != -EAGAIN)
+	if (ret && ret != -EAGAIN && ret != -EINTR)
 		KVM_UV_EVENT(kvm, 3, "PROTVIRT VM UNPACK: failed addr %llx with rc %x rrc %x",
 			     uvcb.gaddr, *rc, *rrc);
 	return ret;
-- 
2.55.0

[PATCH v4 08/13] KVM: s390: Free the mmu cache when kvm_arch_vcpu_create() fails

[Claudio Imbrenda]

The mmu cache is the first thing that is allocated in
kvm_arch_vcpu_create(), but in case of failure it was not freed.

Fix by freeing the mmu cache in case of failure.

Refactor kvm_arch_vcpu_create() to use scope-based cleanup instead of
gotos.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
---
 arch/s390/kvm/kvm-s390.c | 40 ++++++++++++++++++----------------------
 1 file changed, 18 insertions(+), 22 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 47eba1664bec..776dfa0ef970 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3795,21 +3795,21 @@ int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id)
 	return 0;
 }
 
+DEFINE_FREE(sie_page, struct sie_page *, if (_T) free_page((unsigned long)(_T)))
+
 int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 {
-	struct sie_page *sie_page;
+	struct kvm_s390_mmu_cache *mc __free(kvm_s390_mmu_cache) = NULL;
+	struct sie_page *sie_page __free(sie_page) = NULL;
 	int rc;
 
 	BUILD_BUG_ON(sizeof(struct sie_page) != 4096);
-	vcpu->arch.mc = kvm_s390_new_mmu_cache();
-	if (!vcpu->arch.mc)
+	mc = kvm_s390_new_mmu_cache();
+	if (!mc)
 		return -ENOMEM;
 	sie_page = (struct sie_page *) get_zeroed_page(GFP_KERNEL_ACCOUNT);
-	if (!sie_page) {
-		kvm_s390_free_mmu_cache(vcpu->arch.mc);
-		vcpu->arch.mc = NULL;
+	if (!sie_page)
 		return -ENOMEM;
-	}
 
 	vcpu->arch.sie_block = &sie_page->sie_block;
 	vcpu->arch.sie_block->itdba = virt_to_phys(&sie_page->itdb);
@@ -3851,10 +3851,9 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 		vcpu->run->kvm_valid_regs |= KVM_SYNC_FPRS;
 
 	if (kvm_is_ucontrol(vcpu->kvm)) {
-		rc = -ENOMEM;
 		vcpu->arch.gmap = gmap_new_child(vcpu->kvm->arch.gmap, -1UL);
 		if (!vcpu->arch.gmap)
-			goto out_free_sie_block;
+			return -ENOMEM;
 	}
 
 	VM_EVENT(vcpu->kvm, 3, "create cpu %d at 0x%p, sie block at 0x%p",
@@ -3862,22 +3861,19 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	trace_kvm_s390_create_vcpu(vcpu->vcpu_id, vcpu, vcpu->arch.sie_block);
 
 	rc = kvm_s390_vcpu_setup(vcpu);
-	if (rc)
-		goto out_ucontrol_uninit;
+	if (rc) {
+		if (kvm_is_ucontrol(vcpu->kvm)) {
+			scoped_guard(spinlock, &vcpu->kvm->arch.gmap->children_lock)
+				gmap_remove_child(vcpu->arch.gmap);
+			vcpu->arch.gmap = gmap_put(vcpu->arch.gmap);
+		}
+		return rc;
+	}
 
+	vcpu->arch.mc = no_free_ptr(mc);
+	sie_page = NULL;
 	kvm_s390_update_topology_change_report(vcpu->kvm, 1);
 	return 0;
-
-out_ucontrol_uninit:
-	if (kvm_is_ucontrol(vcpu->kvm)) {
-		spin_lock(&vcpu->kvm->arch.gmap->children_lock);
-		gmap_remove_child(vcpu->arch.gmap);
-		spin_unlock(&vcpu->kvm->arch.gmap->children_lock);
-		vcpu->arch.gmap = gmap_put(vcpu->arch.gmap);
-	}
-out_free_sie_block:
-	free_page((unsigned long)(vcpu->arch.sie_block));
-	return rc;
 }
 
 int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
-- 
2.55.0

[PATCH v4 09/13] KVM: s390: Fix ordering when adding to SCA

[Claudio Imbrenda]

When adding a new vCPU to the SCA area, the validity bit in the MCN was
set before the pointer to the state description, potentially allowing
for a race.

Fix by setting the pointer before setting the bit.

Fixes: 14542a0a54c5 ("KVM: S390: Remove sca_lock")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 776dfa0ef970..59f784f8c01b 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3481,8 +3481,8 @@ static void sca_add_vcpu(struct kvm_vcpu *vcpu)
 	if (!kvm_s390_use_sca_entries())
 		return;
 
+	WRITE_ONCE(sca->cpu[vcpu->vcpu_id].sda, virt_to_phys(vcpu->arch.sie_block));
 	set_bit_inv(vcpu->vcpu_id, (unsigned long *)sca->mcn);
-	sca->cpu[vcpu->vcpu_id].sda = virt_to_phys(vcpu->arch.sie_block);
 }
 
 static int sca_can_add_vcpu(struct kvm *kvm, unsigned int id)
-- 
2.55.0

[PATCH v4 10/13] KVM: s390: Fix cleanup in kvm_s390_pv_create_cpu()

[Claudio Imbrenda]

If creating a protected vCPU in kvm_s390_pv_create_cpu() fails,
kvm_s390_pv_destroy_cpu() was called, which checks whether the vCPU has
a PV handle and exits doing nothing otherwise. At that point, due to
not having created the protected vCPU, the PV handle will not be set,
and kvm_s390_pv_destroy_cpu() will do nothing, thus leaking the
allocated memory.

Fix by factoring out the code to free and reset a PV vCPU; call it from
kvm_s390_pv_destroy_cpu() and kvm_s390_pv_create_cpu().

Opportunistically fix the return value of kvm_s390_pv_destroy_cpu() in
case of errors: return -EIO instead if EIO.

Fixes: d4074324b07a ("KVM: s390: pv: avoid double free of sida page")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
---
 arch/s390/kvm/pv.c | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index dc204b521052..b02e0159d3cd 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -244,6 +244,24 @@ static void kvm_s390_clear_pv_state(struct kvm *kvm)
 	kvm->arch.pv.stor_var = NULL;
 }
 
+static void kvm_s390_pv_dispose_cpu(struct kvm_vcpu *vcpu, bool free_stor_base)
+{
+	if (free_stor_base)
+		free_pages(vcpu->arch.pv.stor_base, get_order(uv_info.guest_cpu_stor_len));
+	free_page((unsigned long)sida_addr(vcpu->arch.sie_block));
+	vcpu->arch.sie_block->pv_handle_cpu = 0;
+	vcpu->arch.sie_block->pv_handle_config = 0;
+	memset(&vcpu->arch.pv, 0, sizeof(vcpu->arch.pv));
+	vcpu->arch.sie_block->sdf = 0;
+	/*
+	 * The sidad field (for sdf == 2) is now the gbea field (for sdf == 0).
+	 * Use the reset value of gbea to avoid leaking the kernel pointer of
+	 * the just freed sida.
+	 */
+	vcpu->arch.sie_block->gbea = 1;
+	kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+}
+
 int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
 {
 	int cc;
@@ -258,24 +276,9 @@ int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
 	WARN_ONCE(cc, "protvirt destroy cpu failed rc %x rrc %x", *rc, *rrc);
 
 	/* Intended memory leak for something that should never happen. */
-	if (!cc)
-		free_pages(vcpu->arch.pv.stor_base,
-			   get_order(uv_info.guest_cpu_stor_len));
-
-	free_page((unsigned long)sida_addr(vcpu->arch.sie_block));
-	vcpu->arch.sie_block->pv_handle_cpu = 0;
-	vcpu->arch.sie_block->pv_handle_config = 0;
-	memset(&vcpu->arch.pv, 0, sizeof(vcpu->arch.pv));
-	vcpu->arch.sie_block->sdf = 0;
-	/*
-	 * The sidad field (for sdf == 2) is now the gbea field (for sdf == 0).
-	 * Use the reset value of gbea to avoid leaking the kernel pointer of
-	 * the just freed sida.
-	 */
-	vcpu->arch.sie_block->gbea = 1;
-	kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+	kvm_s390_pv_dispose_cpu(vcpu, !cc);
 
-	return cc ? EIO : 0;
+	return cc ? -EIO : 0;
 }
 
 int kvm_s390_pv_create_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
@@ -319,9 +322,7 @@ int kvm_s390_pv_create_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
 		     uvcb.header.rrc);
 
 	if (cc) {
-		u16 dummy;
-
-		kvm_s390_pv_destroy_cpu(vcpu, &dummy, &dummy);
+		kvm_s390_pv_dispose_cpu(vcpu, true);
 		return -EIO;
 	}
 
-- 
2.55.0

[PATCH v4 11/13] KVM: s390: Fix kvm_arch_commit_memory_region() when low on memory

[Claudio Imbrenda]

When low on memory, kvm_arch_commit_memory_region() might not perform
the required action completely, and instead just print a warning and
return. This allows the VM to continue running with an inconsistent
state.

Fix by refilling the struct kvm_s390_mmu_cache and trying again. A true
failure only happens if the refill fails, or if the cache cannot be
allocated at all; in such case print a warning and kill the VM. Such a
failure cannot currently happen.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
---
 arch/s390/kvm/kvm-s390.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 59f784f8c01b..b151d25a4a4c 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5817,7 +5817,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 {
 	const struct dat_walk_ops ops = { .pte_entry = cmma_d_count_pte, };
 	struct kvm_s390_mmu_cache *mc __free(kvm_s390_mmu_cache) = NULL;
-	int rc = 0;
+	int rc = -ENOMEM;
 
 	guard(mutex)(&kvm->slots_arch_lock);
 
@@ -5825,11 +5825,9 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 		return;
 
 	mc = kvm_s390_new_mmu_cache();
-	if (!mc) {
-		rc = -ENOMEM;
+	if (!mc)
 		goto out;
-	}
-
+retry:
 	scoped_guard(write_lock, &kvm->mmu_lock) {
 		if (kvm->arch.migration_mode && kvm->arch.use_cmma && old) {
 			_dat_walk_gfn_range(old->base_gfn, old->base_gfn + old->npages,
@@ -5852,11 +5850,17 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 		case KVM_MR_FLAGS_ONLY:
 			break;
 		default:
+			rc = 0;
 			WARN(1, "Unknown KVM MR CHANGE: %d\n", change);
 		}
 	}
+	if (rc == -ENOMEM) {
+		rc = kvm_s390_mmu_cache_topup(mc);
+		if (!rc)
+			goto retry;
+	}
 out:
-	if (rc)
+	if (KVM_BUG_ON(rc, kvm))
 		pr_warn("failed to commit memory region\n");
 	return;
 }
-- 
2.55.0

[PATCH v4 12/13] KVM: s390: Fix kvm_s390_vcpu_unsetup_cmma()

[Claudio Imbrenda]

In some cases kvm_s390_vcpu_unsetup_cmma() can be called with a 0
cbrlo; in such cases, if running with V != R, free_page() will attempt
to free physical page 0.

Fix by freeing cbrlo only if it's non-zero.

Fixes: b31605c12f4e ("KVM: s390: make cmma usage conditionally")
Fixes: 29b40f105ec8 ("KVM: s390: protvirt: Add initial vm and cpu lifecycle handling")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index b151d25a4a4c..84c6f77e9fc9 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3677,7 +3677,8 @@ static void kvm_s390_vcpu_crypto_setup(struct kvm_vcpu *vcpu)
 
 void kvm_s390_vcpu_unsetup_cmma(struct kvm_vcpu *vcpu)
 {
-	free_page((unsigned long)phys_to_virt(vcpu->arch.sie_block->cbrlo));
+	if (vcpu->arch.sie_block->cbrlo)
+		free_page((unsigned long)phys_to_virt(vcpu->arch.sie_block->cbrlo));
 	vcpu->arch.sie_block->cbrlo = 0;
 }
 
-- 
2.55.0

[PATCH v4 13/13] KVM: s390: Fix sca_clear_ext_call() for UCONTROL

[Claudio Imbrenda]

When cleaning up a UCONTROL VM, sca_clear_ext_call() will touch memory
outside of the allocated ESCA block, and UCONTROL VMs don't even use
ESCA.

Fix by not touching ESCA for UCONTROL VMs.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes: 7d43bafcff17 ("KVM: s390: Make provisions for ESCA utilization")
---
 arch/s390/kvm/interrupt.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 2acdff130fa6..8d146a0681dc 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -84,10 +84,13 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
 static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
 {
 	struct esca_block *sca = vcpu->kvm->arch.sca;
-	union esca_sigp_ctrl *sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl;
+	union esca_sigp_ctrl *sigp_ctrl;
 
-	if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized)
+	if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized || kvm_is_ucontrol(vcpu->kvm))
 		return;
+
+	/* Initialize after the above check, to prevent going out of bounds */
+	sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl;
 	kvm_s390_clear_cpuflags(vcpu, CPUSTAT_ECALL_PEND);
 
 	WRITE_ONCE(sigp_ctrl->value, 0);
-- 
2.55.0