KVM: s390: Use try_cmpxchg() instead of cmpxchg() loops

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.

Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20241126102515.3178914-2-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index a688351f4ab5217d745444e6b8a95829c10a2f1f..9816b0060fbe541909c29818e88aeb2d3ef60749 100644 (file)
--- 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 @@ retry:
                }
                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 @@ retry:
                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 4f0e7f61edf788bf94e10b9265f71436790bdf73..eff69018cbebfa5acc36a5ae6513fa0df87bccbd 100644 (file)
--- 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 deeb32034ad5e98779795df61666afffa73549a9..a1fcdb2479a110d18e11237127a72be66446335a 100644 (file)
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1907,11 +1907,11 @@ 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 a61518b549f00b108693b432a5e57114214a69b8..9b9e7fdd53807886cd24cda103f8f46650ddf53f 100644 (file)
--- 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);