Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: > On 1/26/22 16:56, Vitaly Kuznetsov wrote: >>> - WARN_ON(loaded_vmcs == &vmx->vmcs01 && loaded_vmcs->shadow_vmcs); >>> + if (WARN_ON(loaded_vmcs != &vmx->vmcs01 || loaded_vmcs->shadow_vmcs)) >>> + return loaded_vmcs->shadow_vmcs; >> Stupid question: why do we want to care about 'loaded_vmcs' at all, >> i.e. why can't we hardcode 'vmx->vmcs01' in alloc_shadow_vmcs()? The >> only caller is enter_vmx_operation() and AFAIU 'loaded_vmcs' will always >> be pointing to 'vmx->vmcs01' (as enter_vmx_operation() allocates >> &vmx->nested.vmcs02 so 'loaded_vmcs' can't point there!). >> > > Well, that's why the WARN never happens. The idea is that if shadow > VMCS _virtualization_ (not emulation, i.e. running L2 VMREAD/VMWRITE > without even a vmexit to L0) was supported, then you would need a > non-NULL shadow_vmcs in vmx->vmcs02. > > Regarding the patch, the old WARN was messy but it was also trying to > avoid a NULL pointer dereference in the caller. > > What about: > > if (WARN_ON(loaded_vmcs->shadow_vmcs)) > return loaded_vmcs->shadow_vmcs; > > /* Go ahead anyway. */ > WARN_ON(loaded_vmcs != &vmx->vmcs01); > > ? > FWIW, this looks better [to my personal taste]. -- Vitaly
