Re: [RFC PATCH v2 55/69] KVM: VMX: Add 'main.c' to wrap VMX and TDX

[Paolo Bonzini]

On 08/07/21 17:21, Isaku Yamahata wrote:
> On Tue, Jul 06, 2021 at 04:43:22PM +0200,
> Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> > On 03/07/21 00:05, isaku.yamahata@xxxxxxxxx wrote:
> > > +#include "vmx.c"
> >
> > What makes it particularly hard to have this as a separate .o file rather
> > than an #include?
>
> It's to let complier to optimize functionc call of "if (tdx) tdx_xxx() else vmx_xxx()",
> given x86_ops static call story.

As long as it's not an indirect call, not inlining tdx_xxx and vmx_xxx 
is unlikely to give a lot of benefit.

What you could do, is use a static branch that bypasses the 
"is_tdx_vcpu/vm" check if no TDX VM is running.  A similar technique is 
used to bypass the test for in-kernel APIC if all VM have it.

Paolo