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

From: Tom Lendacky <thomas.lendacky@amd.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Sean Christopherson <seanjc@google.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Borislav Petkov <bp@suse.de>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 03/13] KVM: SVM: Move SEV module params/variables to sev.c
Date: Mon, 11 Jan 2021 09:36:29 -0600	[thread overview]
Message-ID: <672e86f7-86c7-0377-c544-fe52c8d7c1b9@amd.com> (raw)
In-Reply-To: <87sg7792l3.fsf@vitty.brq.redhat.com>

On 1/11/21 4:42 AM, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.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@google.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?

I thought it was a review comment, but I'm not able to find it now.

Brijesh probably remembers better than me.

> 
> 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?

This will still result in an overall sev=0 sev_es=0. Is the question just 
about issuing a message based on the initial values specified?

Thanks,
Tom

> 
>> +
>>   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);
> 