This is a note to let you know that I've just added the patch titled KVM: remember position in kvm->vcpus array to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-remember-position-in-kvm-vcpus-array.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 8750e72a79dda2f665ce17b62049f4d62130d991 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@xxxxxxxxxx> Date: Thu, 7 Nov 2019 07:53:42 -0500 Subject: KVM: remember position in kvm->vcpus array MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Radim Krčmář <rkrcmar@xxxxxxxxxx> commit 8750e72a79dda2f665ce17b62049f4d62130d991 upstream. Fetching an index for any vcpu in kvm->vcpus array by traversing the entire array everytime is costly. This patch remembers the position of each vcpu in kvm->vcpus array by storing it in vcpus_idx under kvm_vcpu structure. Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx> Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> [borntraeger@xxxxxxxxxx]: backport to 4.19 (also fits for 5.4) Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/kvm_host.h | 11 +++-------- virt/kvm/kvm_main.c | 5 +++-- 2 files changed, 6 insertions(+), 10 deletions(-) --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -266,7 +266,8 @@ struct kvm_vcpu { struct preempt_notifier preempt_notifier; #endif int cpu; - int vcpu_id; + int vcpu_id; /* id given by userspace at creation */ + int vcpu_idx; /* index in kvm->vcpus array */ int srcu_idx; int mode; u64 requests; @@ -571,13 +572,7 @@ static inline struct kvm_vcpu *kvm_get_v static inline int kvm_vcpu_get_idx(struct kvm_vcpu *vcpu) { - struct kvm_vcpu *tmp; - int idx; - - kvm_for_each_vcpu(idx, tmp, vcpu->kvm) - if (tmp == vcpu) - return idx; - BUG(); + return vcpu->vcpu_idx; } #define kvm_for_each_memslot(memslot, slots) \ --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2864,7 +2864,8 @@ static int kvm_vm_ioctl_create_vcpu(stru goto unlock_vcpu_destroy; } - BUG_ON(kvm->vcpus[atomic_read(&kvm->online_vcpus)]); + vcpu->vcpu_idx = atomic_read(&kvm->online_vcpus); + BUG_ON(kvm->vcpus[vcpu->vcpu_idx]); /* Now it's all set up, let userspace reach it */ kvm_get_kvm(kvm); @@ -2874,7 +2875,7 @@ static int kvm_vm_ioctl_create_vcpu(stru goto unlock_vcpu_destroy; } - kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu; + kvm->vcpus[vcpu->vcpu_idx] = vcpu; /* * Pairs with smp_rmb() in kvm_get_vcpu. Write kvm->vcpus Patches currently in stable-queue which might be from rkrcmar@xxxxxxxxxx are queue-5.4/kvm-remember-position-in-kvm-vcpus-array.patch