Re: [PATCH v4 04/18] KVM: SEV: Wire up kvm_x86_ops.gmem_xxx() if and only if CONFIG_KVM_AMD_SEV=y

[Sean Christopherson <seanjc@google.com>]

On Thu, Jul 09, 2026, Ackerley Tng wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > Wire up the SEV-SNP guest_memfd kvm_x86_ops hooks if and only if SEV is
> > actually enabled, and drop the now-unnecessary stubs.  Leaving the hooks
> > NULL allows the static call infrastructure to elide the CALL+RET, and more
> > importantly, referencing the hooks if and only if SEV support is enabled
> > will allow conditionally definining the hooks using their corresponding
> > HAVE_KVM_ARCH_GMEM_XXX Kconfig.
> >
> > No functional change intended.
> >
> > Cc: stable@vger.kernel.org # 6.12.x
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  arch/x86/kvm/svm/svm.c |  8 ++++----
> >  arch/x86/kvm/svm/svm.h | 10 ----------
> >  2 files changed, 4 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index ef69a51ab27f..79c818d91dda 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -5448,6 +5448,10 @@ struct kvm_x86_ops svm_x86_ops __initdata = {
> >
> >  	.vm_copy_enc_context_from = sev_vm_copy_enc_context_from,
> >  	.vm_move_enc_context_from = sev_vm_move_enc_context_from,
> > +
> > +	.gmem_prepare = sev_gmem_prepare,
> 
> Here .gmem_prepare assignment is gated on CONFIG_KVM_AMD_SEV but later
> the definition of .gmem_prepare is gated on
> CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE.
> 
> CONFIG_KVM_AMD_SEV selects CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE, but I
> wonder if there's a chance due to config disconnects this will cause
> compilation issues? Like .gmem_prepare will get assigned but it was not
> declared? Or is that actually intentional?

Intentional.  If we end up with KVM_AMD_SEV=y, but HAVE_KVM_ARCH_GMEM_PREPARE=n,
then I definitely want the build to fail.