Re: [PATCH] KVM: SVM: Add a helper to get LBR field pointer to dedup MSR accesses

[Sean Christopherson <seanjc@google.com>]

On Fri, Mar 13, 2026, Yosry Ahmed wrote:
> > Hrm, I was assuming the compiler would be smart to understand the other cases
> > are unreachable.  What clang version, and are you doing anything special with
> > your config?
> 
> Debian clang version 18.1.8 (20+build1)
> 
> Nothing special with my config AFAICT.

Lame.  Given that it's Friday and I'm about to become a pumpkin, and it doesn't
really matter if it's compile-timer assert or not, I'm going to sqaush it to this:

static u64 *svm_vmcb_lbr(struct vcpu_svm *svm, u32 msr)
{
	switch (msr) {
	case MSR_IA32_LASTBRANCHFROMIP:
		return &svm->vmcb->save.br_from;
	case MSR_IA32_LASTBRANCHTOIP:
		return &svm->vmcb->save.br_to;
	case MSR_IA32_LASTINTFROMIP:
		return &svm->vmcb->save.last_excp_from;
	case MSR_IA32_LASTINTTOIP:
		return &svm->vmcb->save.last_excp_to;
	default:
		break;
	}
	KVM_BUG_ON(1, svm->vcpu.kvm);
	return &svm->vmcb->save.br_from;
}

Can you double check that kvm-x86/nested builds for you?  In the process of
rebuilding kvm-x86/next...