On Tue, Oct 15, 2019 at 04:36:57PM +0200, Vitaly Kuznetsov wrote: > Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: > > > On 15/10/19 12:53, Vitaly Kuznetsov wrote: > >> A very theoretical question: why do we have 'struct vcpu' embedded in > >> vcpu_vmx/vcpu_svm and not the other way around (e.g. in a union)? That > >> would've allowed us to allocate memory in common code and then fill in > >> vendor-specific details in .create_vcpu(). A union would waste a non-trivial amount of memory on SVM. SVM: struct size = 14560 VMX: struct size = 16192 There are ways around that, but... > > > > Probably "because it's always been like that" is the most accurate answer. > > > > OK, so let me make my question a bit less theoretical: would you be in > favor of changing the status quo? :-) ... we don't need to invert the strut embedding to re-order the create flow. 'struct kvm_vcpu' must be at offset zero and the size of the vcpu is vendor defined, so kvm_arch_vcpu_create() can allocate the struct and directly cast it to a 'struct kvm_vcpu *'.
