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charset="us-ascii" On Thu, Nov 28, 2024, Xiaoyao Li wrote: > On 11/28/2024 8:43 AM, Sean Christopherson wrote: > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index 11434752b467..39be2a891ab4 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -9982,10 +9982,11 @@ static int complete_hypercall_exit(struct kvm_vcpu *vcpu) > > return kvm_skip_emulated_instruction(vcpu); > > } > > -unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr, > > - unsigned long a0, unsigned long a1, > > - unsigned long a2, unsigned long a3, > > - int op_64_bit, int cpl) > > +int __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr, > > + unsigned long a0, unsigned long a1, > > + unsigned long a2, unsigned long a3, > > + int op_64_bit, int cpl, > > + int (*complete_hypercall)(struct kvm_vcpu *)) > > { > > unsigned long ret; > > @@ -10061,7 +10062,7 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr, > > vcpu->run->hypercall.flags |= KVM_EXIT_HYPERCALL_LONG_MODE; > > WARN_ON_ONCE(vcpu->run->hypercall.flags & KVM_EXIT_HYPERCALL_MBZ); > > - vcpu->arch.complete_userspace_io = complete_hypercall_exit; > > + vcpu->arch.complete_userspace_io = complete_hypercall; > > /* stat is incremented on completion. */ > > return 0; > > } > > @@ -10071,13 +10072,15 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr, > > } > > out: > > - return ret; > > + vcpu->run->hypercall.ret = ret; > > + complete_hypercall(vcpu); > > + return 1; > > shouldn't it be > > return complete_hypercall(vcpu); > > ? Ouch. Yes, it most definitely should be. > Originally, kvm_emulate_hypercall() returns kvm_skip_emulated_instruction(). > Now it becomes > > kvm_skip_emulated_instruction(); > return 1; > > I don't go deep to see if kvm_skip_emulated_instruction() always return 1 > for this case. It doesn't. KVM needs to exit to userspace if userspace is single-stepping, or in the extremely unlikely scenario that KVM can't skip the emulated instruction (which can very theoretically happen on older AMD CPUs).