Re: [PATCH] KVM: X86: Add missing KVM_AMD dependency

[Guenter Roeck <linux@roeck-us.net>]

On Fri, Oct 05, 2018 at 10:41:55PM +0200, Paolo Bonzini wrote:
> On 05/10/2018 20:46, Guenter Roeck wrote:
> > Analysis shows that commit 59414c9892208 ("KVM: SVM: Add support for
> > KVM_SEV_LAUNCH_START command") added a dependency of KVM_AMD on
> > CRYPTO_DEV_CCP_DD if CRYPTO_DEV_SP_PSP is enabled: If CRYPTO_DEV_CCP_DD
> > is built as module, KVM_AMD must be built as module as well.
> > 
> > Fixes: 59414c9892208 ("KVM: SVM: Add support for KVM_SEV_LAUNCH_START command")
> > Cc: Brijesh Singh <brijesh.singh@amd.com>
> > Cc: Borislav Petkov <bp@suse.de>
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> 
> This should be handled by
> 
> config KVM_AMD_SEV
>         def_bool y
>         bool "AMD Secure Encrypted Virtualization (SEV) support"
>         depends on KVM_AMD && X86_64
>         depends on CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m)
>         ---help---
>         Provides support for launching Encrypted VMs on AMD processors.
> 

Unfortunately it doesn't. It disables KVM_AMD_SEV, but that doesn't prevent
the calls.

> Maybe this works as well?  I haven't tested it yet:
> 

I am sure there are many possible solutions. I would personally prefer one
that enforces KVM_AMD=m with CRYPTO_DEV_CCP_DD=m, but that is just me.

Thanks,
Guenter

> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 89c4c5aa15f1..55f10b17d044 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -441,9 +441,13 @@ static inline bool svm_sev_enabled(void)
> 
>  static inline bool sev_guest(struct kvm *kvm)
>  {
> +#ifdef CONFIG_KVM_AMD_SEV
>  	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> 
>  	return sev->active;
> +#else
> +	return false;
> +#endif
>  }
> 
>  static inline int sev_get_asid(struct kvm *kvm)
> 
> Thanks,
> 
> Paolo