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AHgh+RpeZQw9rTapS184NqnpJd9eKyil7IaDrdBdDqVzlnPvh4oJzTPp8tiBqDMsuKbEzMQo1cQ=@vger.kernel.org X-Gm-Message-State: AOJu0YxVWzjK6BcI2vHn/YSuqft9Unb0+LouuPAf/+askS8x2/bEd1dK e/SZenHlF83LWAeqr1yUNhfw98sUSEvYfBm77bkxmXvet8jGBPg6o2yPksve23WxrpiBs2hjWMB rPlWFZQ== X-Received: from pgmc6.prod.google.com ([2002:a63:1c46:0:b0:c9b:5bf6:f971]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:408a:b0:84a:2dcb:5aca with SMTP id d2e1a72fcca58-84c2954df26mr16284618b3a.77.1784589307791; Mon, 20 Jul 2026 16:15:07 -0700 (PDT) Date: Mon, 20 Jul 2026 16:15:07 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260716160801.3155582-1-dmaluka@chromium.org> <792366b7d918faca3f40bccab56bab965e7e34f5.camel@intel.com> Message-ID: Subject: Re: [PATCH] KVM: VMX: Postpone IPIv setup after successful vCPU creation From: Sean Christopherson To: Kai Huang Cc: Chao Gao , "aashish@aashishsharma.net" , "guang.zeng@intel.com" , "dmaluka@chromium.org" , "dave.hansen@linux.intel.com" , "vineeth@bitbyteword.org" , "linux-kernel@vger.kernel.org" , "jaszczyk@chromium.org" , "kvm@vger.kernel.org" , "pbonzini@redhat.com" , Chuanxiao Dong Content-Type: text/plain; charset="us-ascii" On Mon, Jul 20, 2026, Kai Huang wrote: > > E.g. for the xarray approacy (sketch only, completely untested): > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index fdbd697d0337..e34ca5920393 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -791,6 +791,7 @@ struct kvm { > > /* The current active memslot set for each address space */ > > struct kvm_memslots __rcu *memslots[KVM_MAX_NR_ADDRESS_SPACES]; > > struct xarray vcpu_array; > > + struct xarray pending_vcpu_ids; > > /* > > * Protected by slots_lock, but can be read outside if an > > * incorrect answer is acceptable. > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 2df8ee9ecf6c..8bc4f7ffd76d 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -4179,6 +4179,12 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id) > > return r; > > } > > > > + r = xa_insert(&kvm->pending_vcpu_ids, id, xa_mk_value(id), GFP_KERNEL); > > + if (r) { > > + mutex_unlock(&kvm->lock); > > + return r; > > + } > > + > > (No preference between xarray vs bitmap) > > Should we move this before kvm_arch_vcpu_precreate() to avoid any "precreate" > for duplicated vcpu_id? Hmm, I'm not sure. I'm leaning "yes". At a glance, I like the idea. My only concern is that we could consume a garbage @id if kvm_arch_vcpu_precreate() performs additional checks on @id, as x86's implementation does. However, I don't think that's a meaningful concern since kvm_vm_ioctl_create_vcpu() *must* perform at least basic sanity checks. So yeah, I think moving the check before precreate() makes sense.