[PATCH 1/3] KVM: s390: Use try_cmpxchg() instead of cmpxchg() loops

Heiko Carstens
2024-11-25T11:50:46Z

Convert all cmpxchg() loops to try_cmpxchg() loops. With gcc 14 and the
usage of flag output operands in try_cmpxchg() this allows the compiler to
generate slightly better code.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/kvm/gaccess.c | 16 ++++++++--------
arch/s390/kvm/interrupt.c | 12 ++++++------
arch/s390/kvm/kvm-s390.c | 4 ++--
arch/s390/kvm/pci.c | 5 ++---
4 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index a688351f4ab5..9816b0060fbe 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -129,8 +129,8 @@ static void ipte_lock_simple(struct kvm *kvm)
retry:
read_lock(&kvm->arch.sca_lock);
ic = kvm_s390_get_ipte_control(kvm);
+ old = READ_ONCE(*ic);
do {
- old = READ_ONCE(*ic);
if (old.k) {
read_unlock(&kvm->arch.sca_lock);
cond_resched();
@@ -138,7 +138,7 @@ static void ipte_lock_simple(struct kvm *kvm)
}
new = old;
new.k = 1;
- } while (cmpxchg(&ic->val, old.val, new.val) != old.val);
+ } while (!try_cmpxchg(&ic->val, &old.val, new.val));
read_unlock(&kvm->arch.sca_lock);
out:
mutex_unlock(&kvm->arch.ipte_mutex);
@@ -154,11 +154,11 @@ static void ipte_unlock_simple(struct kvm *kvm)
goto out;
read_lock(&kvm->arch.sca_lock);
ic = kvm_s390_get_ipte_control(kvm);
+ old = READ_ONCE(*ic);
do {
- old = READ_ONCE(*ic);
new = old;
new.k = 0;
- } while (cmpxchg(&ic->val, old.val, new.val) != old.val);
+ } while (!try_cmpxchg(&ic->val, &old.val, new.val));
read_unlock(&kvm->arch.sca_lock);
wake_up(&kvm->arch.ipte_wq);
out:
@@ -172,8 +172,8 @@ static void ipte_lock_siif(struct kvm *kvm)
retry:
read_lock(&kvm->arch.sca_lock);
ic = kvm_s390_get_ipte_control(kvm);
+ old = READ_ONCE(*ic);
do {
- old = READ_ONCE(*ic);
if (old.kg) {
read_unlock(&kvm->arch.sca_lock);
cond_resched();
@@ -182,7 +182,7 @@ static void ipte_lock_siif(struct kvm *kvm)
new = old;
new.k = 1;
new.kh++;
- } while (cmpxchg(&ic->val, old.val, new.val) != old.val);
+ } while (!try_cmpxchg(&ic->val, &old.val, new.val));
read_unlock(&kvm->arch.sca_lock);
}

@@ -192,13 +192,13 @@ static void ipte_unlock_siif(struct kvm *kvm)

read_lock(&kvm->arch.sca_lock);
ic = kvm_s390_get_ipte_control(kvm);
+ old = READ_ONCE(*ic);
do {
- old = READ_ONCE(*ic);
new = old;
new.kh--;
if (!new.kh)
new.k = 0;
- } while (cmpxchg(&ic->val, old.val, new.val) != old.val);
+ } 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 4f0e7f61edf7..eff69018cbeb 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -247,12 +247,12 @@ static inline int gisa_set_iam(struct kvm_s390_gisa *gisa, u8 iam)
{
u64 word, _word;

+ word = READ_ONCE(gisa->u64.word[0]);
do {
- word = READ_ONCE(gisa->u64.word[0]);
if ((u64)gisa != word >> 32)
return -EBUSY;
_word = (word & ~0xffUL) | iam;
- } while (cmpxchg(&gisa->u64.word[0], word, _word) != word);
+ } while (!try_cmpxchg(&gisa->u64.word[0], &word, _word));

return 0;
}
@@ -270,10 +270,10 @@ static inline void gisa_clear_ipm(struct kvm_s390_gisa *gisa)
{
u64 word, _word;

+ word = READ_ONCE(gisa->u64.word[0]);
do {
- word = READ_ONCE(gisa->u64.word[0]);
_word = word & ~(0xffUL << 24);
- } while (cmpxchg(&gisa->u64.word[0], word, _word) != word);
+ } while (!try_cmpxchg(&gisa->u64.word[0], &word, _word));
}

/**
@@ -291,14 +291,14 @@ static inline u8 gisa_get_ipm_or_restore_iam(struct kvm_s390_gisa_interrupt *gi)
u8 pending_mask, alert_mask;
u64 word, _word;

+ word = READ_ONCE(gi->origin->u64.word[0]);
do {
- word = READ_ONCE(gi->origin->u64.word[0]);
alert_mask = READ_ONCE(gi->alert.mask);
pending_mask = (u8)(word >> 24) & alert_mask;
if (pending_mask)
return pending_mask;
_word = (word & ~0xffUL) | alert_mask;
- } while (cmpxchg(&gi->origin->u64.word[0], word, _word) != word);
+ } while (!try_cmpxchg(&gi->origin->u64.word[0], &word, _word));

return 0;
}
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 442d4a227c0e..d8080c27d45b 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1937,11 +1937,11 @@ static void kvm_s390_update_topology_change_report(struct kvm *kvm, bool val)

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

diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
index a61518b549f0..9b9e7fdd5380 100644
--- a/arch/s390/kvm/pci.c
+++ b/arch/s390/kvm/pci.c
@@ -208,13 +208,12 @@ static inline int account_mem(unsigned long nr_pages)

page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;

+ cur_pages = atomic_long_read(&user->locked_vm);
do {
- cur_pages = atomic_long_read(&user->locked_vm);
new_pages = cur_pages + nr_pages;
if (new_pages > page_limit)
return -ENOMEM;
- } while (atomic_long_cmpxchg(&user->locked_vm, cur_pages,
- new_pages) != cur_pages);
+ } while (!atomic_long_try_cmpxchg(&user->locked_vm, &cur_pages, new_pages));

atomic64_add(nr_pages, &current->mm->pinned_vm);

--
2.45.2