[GIT PULL 02/10] KVM: S390: Remove sca_lock

Janosch Frank
2025-12-01T12:45:16Z

From: Christoph Schlameuss <schlameuss@linux.ibm.com>

Since we are no longer switching from a BSCA to a ESCA we can completely
get rid of the sca_lock. The write lock was only taken for that
conversion.

After removal of the lock some local code cleanups are possible.

Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Suggested-by: Janosch Frank <frankja@linux.ibm.com>
[frankja@linux.ibm.com: Added suggested-by tag as discussed on list]
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
arch/s390/include/asm/kvm_host.h | 1 -
arch/s390/kvm/gaccess.c | 19 ++---------------
arch/s390/kvm/interrupt.c | 36 ++++++++------------------------
arch/s390/kvm/kvm-s390.c | 34 ++++++++----------------------
4 files changed, 20 insertions(+), 70 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 3cf14dd75409..22cedcaea475 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -633,7 +633,6 @@ struct kvm_s390_pv {

struct kvm_arch {
struct esca_block *sca;
- rwlock_t sca_lock;
debug_info_t *dbf;
struct kvm_s390_float_interrupt float_int;
struct kvm_device *flic;
diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 3651ab682fd7..41ca6b0ee7a9 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -109,14 +109,9 @@ struct aste {

int ipte_lock_held(struct kvm *kvm)
{
- if (sclp.has_siif) {
- int rc;
+ if (sclp.has_siif)
+ return kvm->arch.sca->ipte_control.kh != 0;

- read_lock(&kvm->arch.sca_lock);
- rc = kvm->arch.sca->ipte_control.kh != 0;
- read_unlock(&kvm->arch.sca_lock);
- return rc;
- }
return kvm->arch.ipte_lock_count != 0;
}

@@ -129,19 +124,16 @@ static void ipte_lock_simple(struct kvm *kvm)
if (kvm->arch.ipte_lock_count > 1)
goto out;
retry:
- read_lock(&kvm->arch.sca_lock);
ic = &kvm->arch.sca->ipte_control;
old = READ_ONCE(*ic);
do {
if (old.k) {
- read_unlock(&kvm->arch.sca_lock);
cond_resched();
goto retry;
}
new = old;
new.k = 1;
} while (!try_cmpxchg(&ic->val, &old.val, new.val));
- read_unlock(&kvm->arch.sca_lock);
out:
mutex_unlock(&kvm->arch.ipte_mutex);
}
@@ -154,14 +146,12 @@ static void ipte_unlock_simple(struct kvm *kvm)
kvm->arch.ipte_lock_count--;
if (kvm->arch.ipte_lock_count)
goto out;
- read_lock(&kvm->arch.sca_lock);
ic = &kvm->arch.sca->ipte_control;
old = READ_ONCE(*ic);
do {
new = old;
new.k = 0;
} while (!try_cmpxchg(&ic->val, &old.val, new.val));
- read_unlock(&kvm->arch.sca_lock);
wake_up(&kvm->arch.ipte_wq);
out:
mutex_unlock(&kvm->arch.ipte_mutex);
@@ -172,12 +162,10 @@ static void ipte_lock_siif(struct kvm *kvm)
union ipte_control old, new, *ic;

retry:
- read_lock(&kvm->arch.sca_lock);
ic = &kvm->arch.sca->ipte_control;
old = READ_ONCE(*ic);
do {
if (old.kg) {
- read_unlock(&kvm->arch.sca_lock);
cond_resched();
goto retry;
}
@@ -185,14 +173,12 @@ static void ipte_lock_siif(struct kvm *kvm)
new.k = 1;
new.kh++;
} while (!try_cmpxchg(&ic->val, &old.val, new.val));
- read_unlock(&kvm->arch.sca_lock);
}

static void ipte_unlock_siif(struct kvm *kvm)
{
union ipte_control old, new, *ic;

- read_lock(&kvm->arch.sca_lock);
ic = &kvm->arch.sca->ipte_control;
old = READ_ONCE(*ic);
do {
@@ -201,7 +187,6 @@ static void ipte_unlock_siif(struct kvm *kvm)
if (!new.kh)
new.k = 0;
} while (!try_cmpxchg(&ic->val, &old.val, new.val));
- read_unlock(&kvm->arch.sca_lock);
if (!new.kh)
wake_up(&kvm->arch.ipte_wq);
}
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 36394ba897f5..220d9d00c23d 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -45,48 +45,34 @@ static struct kvm_s390_gib *gib;
/* handle external calls via sigp interpretation facility */
static int sca_ext_call_pending(struct kvm_vcpu *vcpu, int *src_id)
{
- union esca_sigp_ctrl sigp_ctrl;
- struct esca_block *sca;
- int c, scn;
+ struct esca_block *sca = vcpu->kvm->arch.sca;
+ union esca_sigp_ctrl sigp_ctrl = sca->cpu[vcpu->vcpu_id].sigp_ctrl;

if (!kvm_s390_test_cpuflags(vcpu, CPUSTAT_ECALL_PEND))
return 0;

BUG_ON(!kvm_s390_use_sca_entries());
- read_lock(&vcpu->kvm->arch.sca_lock);
- sca = vcpu->kvm->arch.sca;
- sigp_ctrl = sca->cpu[vcpu->vcpu_id].sigp_ctrl;
-
- c = sigp_ctrl.c;
- scn = sigp_ctrl.scn;
- read_unlock(&vcpu->kvm->arch.sca_lock);

if (src_id)
- *src_id = scn;
+ *src_id = sigp_ctrl.scn;

- return c;
+ return sigp_ctrl.c;
}

static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
{
- union esca_sigp_ctrl old_val, new_val = {0};
- union esca_sigp_ctrl *sigp_ctrl;
- struct esca_block *sca;
+ 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 old_val, new_val = {.scn = src_id, .c = 1};
int expect, rc;

BUG_ON(!kvm_s390_use_sca_entries());
- read_lock(&vcpu->kvm->arch.sca_lock);
- sca = vcpu->kvm->arch.sca;
- sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl;

old_val = READ_ONCE(*sigp_ctrl);
- new_val.scn = src_id;
- new_val.c = 1;
old_val.c = 0;

expect = old_val.value;
rc = cmpxchg(&sigp_ctrl->value, old_val.value, new_val.value);
- read_unlock(&vcpu->kvm->arch.sca_lock);

if (rc != expect) {
/* another external call is pending */
@@ -98,18 +84,14 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)

static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
{
- union esca_sigp_ctrl *sigp_ctrl;
- struct esca_block *sca;
+ 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())
return;
kvm_s390_clear_cpuflags(vcpu, CPUSTAT_ECALL_PEND);
- read_lock(&vcpu->kvm->arch.sca_lock);
- sca = vcpu->kvm->arch.sca;
- sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl;

WRITE_ONCE(sigp_ctrl->value, 0);
- read_unlock(&vcpu->kvm->arch.sca_lock);
}

int psw_extint_disabled(struct kvm_vcpu *vcpu)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 78468b96d250..769820e3a243 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1938,14 +1938,12 @@ static void kvm_s390_update_topology_change_report(struct kvm *kvm, bool val)
union sca_utility new, old;
struct esca_block *sca;

- read_lock(&kvm->arch.sca_lock);
sca = kvm->arch.sca;
old = READ_ONCE(sca->utility);
do {
new = old;
new.mtcr = val;
} while (!try_cmpxchg(&sca->utility.val, &old.val, new.val));
- read_unlock(&kvm->arch.sca_lock);
}

static int kvm_s390_set_topo_change_indication(struct kvm *kvm,
@@ -1966,9 +1964,7 @@ static int kvm_s390_get_topo_change_indication(struct kvm *kvm,
if (!test_kvm_facility(kvm, 11))
return -ENXIO;

- read_lock(&kvm->arch.sca_lock);
topo = kvm->arch.sca->utility.mtcr;
- read_unlock(&kvm->arch.sca_lock);

return put_user(topo, (u8 __user *)attr->addr);
}
@@ -3345,7 +3341,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)

if (!sclp.has_64bscao)
alloc_flags |= GFP_DMA;
- rwlock_init(&kvm->arch.sca_lock);
mutex_lock(&kvm_lock);

kvm->arch.sca = alloc_pages_exact(sizeof(*kvm->arch.sca), alloc_flags);
@@ -3530,41 +3525,30 @@ static int __kvm_ucontrol_vcpu_init(struct kvm_vcpu *vcpu)

static void sca_del_vcpu(struct kvm_vcpu *vcpu)
{
- struct esca_block *sca;
+ struct esca_block *sca = vcpu->kvm->arch.sca;

if (!kvm_s390_use_sca_entries())
return;
- read_lock(&vcpu->kvm->arch.sca_lock);
- sca = vcpu->kvm->arch.sca;

clear_bit_inv(vcpu->vcpu_id, (unsigned long *)sca->mcn);
sca->cpu[vcpu->vcpu_id].sda = 0;
- read_unlock(&vcpu->kvm->arch.sca_lock);
}

static void sca_add_vcpu(struct kvm_vcpu *vcpu)
{
- struct esca_block *sca;
- phys_addr_t sca_phys;
+ struct esca_block *sca = vcpu->kvm->arch.sca;
+ phys_addr_t sca_phys = virt_to_phys(sca);

- if (!kvm_s390_use_sca_entries()) {
- sca_phys = virt_to_phys(vcpu->kvm->arch.sca);
-
- /* we still need the basic sca for the ipte control */
- vcpu->arch.sie_block->scaoh = sca_phys >> 32;
- vcpu->arch.sie_block->scaol = sca_phys;
- return;
- }
- read_lock(&vcpu->kvm->arch.sca_lock);
- sca = vcpu->kvm->arch.sca;
- sca_phys = virt_to_phys(sca);
-
- sca->cpu[vcpu->vcpu_id].sda = virt_to_phys(vcpu->arch.sie_block);
+ /* we still need the sca header for the ipte control */
vcpu->arch.sie_block->scaoh = sca_phys >> 32;
vcpu->arch.sie_block->scaol = sca_phys & ESCA_SCAOL_MASK;
vcpu->arch.sie_block->ecb2 |= ECB2_ESCA;
+
+ if (!kvm_s390_use_sca_entries())
+ return;
+
set_bit_inv(vcpu->vcpu_id, (unsigned long *)sca->mcn);
- read_unlock(&vcpu->kvm->arch.sca_lock);
+ 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)
--
2.52.0