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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 On 9/21/26 15:57, Thorsten Leemhuis wrote: > On 9/14/26 20:12, Sean Christopherson wrote: >> Serialize vCPU creation by holding kvm->lock for the entirety of >> kvm_vm_ioctl_create_vcpu(), and then revert the now-redundant tracking adding >> by commit 97d65b544f48 ("KVM: Check for duplicate vcpu_id as early as >> possible"). I botched the math when justifying the vcpu_ids tracking; it's not >> an extra 256 bytes, it's an extra 2048 bytes. Roughly doubling the size of >> "struct kvm" tripped x86's KVM_SANITY_CHECK_VM_STRUCT_SIZE, and obviously isn't >> something we want to do in general. > > Hi Sean! Thx for handling this and sorry for pestering you, but I have > to ask, as this fixes a regression that was already reported two times > and introduced this cycle: > > What's the plan to merge this? Is this aimed for the current or the next > merge window? Ciao, Thorsten For this one, but after fixing the PPC and s390 cases. Sean, if you're busy I can send the v2 myself. Paolo >> The TL;DR of why it's a-ok to serialize vCPU creation is that no VMM actually >> does parallel vCPU creation. As with so many things, KVM's current behavior is >> the result of decades-old cruft, not intentional, deliberate design. >> >> Patch 1 is a tangentially related bug fix; I included it here because holding >> kvm->lock for all of vCPU creation allows WARNing if KVM attempts to lock all >> vCPUs if vCPU creation is in-progress (the caller is must hold kvm->lock). >> >> Sean Christopherson (5): >> KVM: Reject attempts to lock all vCPUs if vCPU creation is in-progress >> KVM: Protect all of kvm_vm_ioctl_create_vcpu() with kvm->lock >> KVM: Move check for existing vCPU ID to the top of vCPU creation >> Revert "KVM: Check for duplicate vcpu_id as early as possible" >> KVM: WARN if vCPU creation is in-progress when locking all vCPUs >> >> arch/x86/kvm/svm/sev.c | 10 ---------- >> arch/x86/kvm/vmx/tdx.c | 5 ----- >> include/linux/kvm_host.h | 1 - >> virt/kvm/kvm_main.c | 35 +++++++++++------------------------ >> 4 files changed, 11 insertions(+), 40 deletions(-) >> >> >> base-commit: d599822bdb66aeec5ec76297b0fc6efaaeefe07c > >