Re: [PATCH v2 01/25] KVM: x86/mmu: avoid indirect call for get_cr3

[Paolo Bonzini]

On 3/8/22 17:16, Sean Christopherson wrote:
> > +static inline unsigned long kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
> Wrap the params, no reason to make this line so long.
>
> > +{
> > +#ifdef CONFIG_RETPOLINE
> > +	if (mmu->get_guest_pgd == kvm_get_guest_cr3)
> > +		return kvm_read_cr3(vcpu);
> This is unnecessarily fragile and confusing at first glance.  Compilers are smart
> enough to generate a non-inline version of functions if they're used for function
> pointers, while still inlining where appropriate.  In other words, just drop
> kvm_get_guest_cr3() entirely, a al get_pdptr => kvm_pdptr_read().

Unfortunately this isn't entirely true.  The function pointer will not 
match between compilation units, in this case between the one that calls 
kvm_mmu_get_guest_pgd and the one that assigned kvm_read_cr3 to the 
function pointer.

Paolo