linux-kernel - Re: [PATCH v2 08/14] KVM: SVM: Condition sev_enabled and sev_es_enabled on CONFIG_KVM_AMD

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Date:   Thu, 14 Jan 2021 14:56:09 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v2 08/14] KVM: SVM: Condition sev_enabled and
 sev_es_enabled on CONFIG_KVM_AMD_SEV=y

On 1/13/21 6:37 PM, Sean Christopherson wrote:
> Define sev_enabled and sev_es_enabled as 'false' and explicitly #ifdef
> out all of sev_hardware_setup() if CONFIG_KVM_AMD_SEV=n.  This kills
> three birds at once:
> 
>    - Makes sev_enabled and sev_es_enabled off by default if
>      CONFIG_KVM_AMD_SEV=n.  Previously, they could be on by default if
>      CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y, regardless of KVM SEV
>      support.
> 
>    - Hides the sev and sev_es module params when CONFIG_KVM_AMD_SEV=n.
> 
>    - Resolves a false positive -Wnonnull in __sev_recycle_asids() that is
>      currently masked by the equivalent IS_ENABLED(CONFIG_KVM_AMD_SEV)
>      check in svm_sev_enabled(), which will be dropped in a future patch.
> 
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed by: Tom Lendacky <thomas.lendacky@....com>

> ---
>   arch/x86/kvm/svm/sev.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a024edabaca5..02a66008e9b9 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -28,12 +28,17 @@
>   #define __ex(x) __kvm_handle_fault_on_reboot(x)
>   
>   /* enable/disable SEV support */
> +#ifdef CONFIG_KVM_AMD_SEV
>   static bool sev_enabled = IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT);
>   module_param_named(sev, sev_enabled, bool, 0444);
>   
>   /* enable/disable SEV-ES support */
>   static bool sev_es_enabled = IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT);
>   module_param_named(sev_es, sev_es_enabled, bool, 0444);
> +#else
> +#define sev_enabled false
> +#define sev_es_enabled false
> +#endif /* CONFIG_KVM_AMD_SEV */
>   
>   static u8 sev_enc_bit;
>   static int sev_flush_asids(void);
> @@ -1253,11 +1258,12 @@ void sev_vm_destroy(struct kvm *kvm)
>   
>   void __init sev_hardware_setup(void)
>   {
> +#ifdef CONFIG_KVM_AMD_SEV
>   	unsigned int eax, ebx, ecx, edx;
>   	bool sev_es_supported = false;
>   	bool sev_supported = false;
>   
> -	if (!IS_ENABLED(CONFIG_KVM_AMD_SEV) || !sev_enabled)
> +	if (!sev_enabled)
>   		goto out;
>   
>   	/* Does the CPU support SEV? */
> @@ -1311,6 +1317,7 @@ void __init sev_hardware_setup(void)
>   out:
>   	sev_enabled = sev_supported;
>   	sev_es_enabled = sev_es_supported;
> +#endif
>   }
>   
>   void sev_hardware_teardown(void)
>