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);
?
Paolo
