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

[Ackerley Tng]

Sean Christopherson <seanjc@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx # 6.12.x
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  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?

Reviewed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

> +	.gmem_invalidate = sev_gmem_invalidate,
> +	.gmem_max_mapping_level = sev_gmem_max_mapping_level,
>  #endif
>  	.check_emulate_instruction = svm_check_emulate_instruction,
>
> @@ -5459,10 +5463,6 @@ struct kvm_x86_ops svm_x86_ops __initdata = {
>  	.vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector,
>  	.vcpu_get_apicv_inhibit_reasons = avic_vcpu_get_apicv_inhibit_reasons,
>  	.alloc_apic_backing_page = svm_alloc_apic_backing_page,
> -
> -	.gmem_prepare = sev_gmem_prepare,
> -	.gmem_invalidate = sev_gmem_invalidate,
> -	.gmem_max_mapping_level = sev_gmem_max_mapping_level,
>  };
>
>  /*
>
> [...snip...]
>