Messages in this thread Patch in this message | | | From | "Maciej S. Szmigiero" <> | Subject | [PATCH 2/3] KVM: Use atomic_long_cmpxchg() instead of an open-coded variant | Date | Fri, 26 Nov 2021 01:31:08 +0100 |
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From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
Open-coding a cmpxchg()-like operation is significantly less readable than a direct call.
Also, the open-coded version compiles to multiple instructions with a branch on x86, instead of just a single instruction.
Since technically the open-coded variant didn't guarantee actual atomicity add a comment there, too, that this property isn't strictly required in this case.
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> --- virt/kvm/kvm_main.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index d4399db06d49..367c1cba26d2 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1378,8 +1378,12 @@ static void kvm_replace_memslot(struct kvm *kvm, hash_del(&old->id_node[idx]); interval_tree_remove(&old->hva_node[idx], &slots->hva_tree); - if ((long)old == atomic_long_read(&slots->last_used_slot)) - atomic_long_set(&slots->last_used_slot, (long)new); + /* + * The atomicity isn't strictly required here since we are + * operating on an inactive memslots set anyway. + */ + atomic_long_cmpxchg(&slots->last_used_slot, + (unsigned long)old, (unsigned long)new); if (!new) { kvm_erase_gfn_node(slots, old);
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