From 1d5e740d518e02cea46325b3d37135bf9c08982a Mon Sep 17 00:00:00 2001 From: Zeng Guang Date: Tue, 19 Apr 2022 23:44:09 +0800 Subject: [PATCH] KVM: Move kvm_arch_vcpu_precreate() under kvm->lock kvm_arch_vcpu_precreate() targets to handle arch specific VM resource to be prepared prior to the actual creation of vCPU. For example, x86 platform may need do per-VM allocation based on max_vcpu_ids at the first vCPU creation. It probably leads to concurrency control on this allocation as multiple vCPU creation could happen simultaneously. From the architectual point of view, it's necessary to execute kvm_arch_vcpu_precreate() under protect of kvm->lock. Currently only arm64, x86 and s390 have non-nop implementations at the stage of vCPU pre-creation. Remove the lock acquiring in s390's design and make sure all architecture can run kvm_arch_vcpu_precreate() safely under kvm->lock without recrusive lock issue. Suggested-by: Sean Christopherson Signed-off-by: Zeng Guang Message-Id: <20220419154409.11842-1-guang.zeng@intel.com> Signed-off-by: Paolo Bonzini --- arch/s390/kvm/kvm-s390.c | 2 -- arch/x86/kvm/x86.c | 2 +- virt/kvm/kvm_main.c | 10 ++++++---- 3 files changed, 7 insertions(+), 7 deletions(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index ff457a77e22b..72bd5c9b9617 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3238,9 +3238,7 @@ static int sca_can_add_vcpu(struct kvm *kvm, unsigned int id) if (!sclp.has_esca || !sclp.has_64bscao) return false; - mutex_lock(&kvm->lock); rc = kvm->arch.use_esca ? 0 : sca_switch_to_extended(kvm); - mutex_unlock(&kvm->lock); return rc == 0 && id < KVM_S390_ESCA_CPU_SLOTS; } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 501606e02688..9c2e2b6d1767 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11242,7 +11242,7 @@ static int sync_regs(struct kvm_vcpu *vcpu) int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id) { - if (kvm_check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0) + if (kvm_check_tsc_unstable() && kvm->created_vcpus) pr_warn_once("kvm: SMP vm created on host with unstable TSC; " "guest TSC will not be reliable\n"); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7f79abdbd68d..6dbdcbda0291 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3768,13 +3768,15 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) return -EINVAL; } + r = kvm_arch_vcpu_precreate(kvm, id); + if (r) { + mutex_unlock(&kvm->lock); + return r; + } + kvm->created_vcpus++; mutex_unlock(&kvm->lock); - r = kvm_arch_vcpu_precreate(kvm, id); - if (r) - goto vcpu_decrement; - vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL_ACCOUNT); if (!vcpu) { r = -ENOMEM;