linux-kernel - Re: [PATCH 03/13] KVM: SVM: Move SEV module params/variables to sev.c

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Date:   Mon, 11 Jan 2021 11:42:48 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...e.de>,
        Brijesh Singh <brijesh.singh@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 03/13] KVM: SVM: Move SEV module params/variables to sev.c

Sean Christopherson <seanjc@...gle.com> writes:

> Unconditionally invoke sev_hardware_setup() when configuring SVM and
> handle clearing the module params/variable 'sev' and 'sev_es' in
> sev_hardware_setup().  This allows making said variables static within
> sev.c and reduces the odds of a collision with guest code, e.g. the guest
> side of things has already laid claim to 'sev_enabled'.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/sev.c | 11 +++++++++++
>  arch/x86/kvm/svm/svm.c | 15 +--------------
>  arch/x86/kvm/svm/svm.h |  2 --
>  3 files changed, 12 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 0eeb6e1b803d..8ba93b8fa435 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -27,6 +27,14 @@
>  
>  #define __ex(x) __kvm_handle_fault_on_reboot(x)
>  
> +/* enable/disable SEV support */
> +static int sev = IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT);
> +module_param(sev, int, 0444);
> +
> +/* enable/disable SEV-ES support */
> +static int sev_es = IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT);
> +module_param(sev_es, int, 0444);

Two stupid questions (and not really related to your patch) for
self-eduacation if I may:

1) Why do we rely on CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT (which
sound like it control the guest side of things) to set defaults here? 

2) It appears to be possible to do 'modprobe kvm_amd sev=0 sev_es=1' and
this looks like a bogus configuration, should we make an effort to
validate the correctness upon module load?

> +
>  static u8 sev_enc_bit;
>  static int sev_flush_asids(void);
>  static DECLARE_RWSEM(sev_deactivate_lock);
> @@ -1249,6 +1257,9 @@ void __init sev_hardware_setup(void)
>  	bool sev_es_supported = false;
>  	bool sev_supported = false;
>  
> +	if (!IS_ENABLED(CONFIG_KVM_AMD_SEV) || !sev)
> +		goto out;
> +
>  	/* Does the CPU support SEV? */
>  	if (!boot_cpu_has(X86_FEATURE_SEV))
>  		goto out;
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index ccf52c5531fb..f89f702b2a58 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -189,14 +189,6 @@ module_param(vls, int, 0444);
>  static int vgif = true;
>  module_param(vgif, int, 0444);
>  
> -/* enable/disable SEV support */
> -int sev = IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT);
> -module_param(sev, int, 0444);
> -
> -/* enable/disable SEV-ES support */
> -int sev_es = IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT);
> -module_param(sev_es, int, 0444);
> -
>  bool __read_mostly dump_invalid_vmcb;
>  module_param(dump_invalid_vmcb, bool, 0644);
>  
> @@ -976,12 +968,7 @@ static __init int svm_hardware_setup(void)
>  		kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE);
>  	}
>  
> -	if (IS_ENABLED(CONFIG_KVM_AMD_SEV) && sev) {
> -		sev_hardware_setup();
> -	} else {
> -		sev = false;
> -		sev_es = false;
> -	}
> +	sev_hardware_setup();
>  
>  	svm_adjust_mmio_mask();
>  
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 0fe874ae5498..8e169835f52a 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -408,8 +408,6 @@ static inline bool gif_set(struct vcpu_svm *svm)
>  #define MSR_CR3_LONG_MBZ_MASK			0xfff0000000000000U
>  #define MSR_INVALID				0xffffffffU
>  
> -extern int sev;
> -extern int sev_es;
>  extern bool dump_invalid_vmcb;
>  
>  u32 svm_msrpm_offset(u32 msr);

-- 
Vitaly