linux-kernel - Re: [PATCH v9 14/22] KVM: s390: interfaces to clear CRYCB masks

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Date:   Wed, 15 Aug 2018 13:55:51 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com,
        frankja@...ux.ibm.com
Subject: Re: [PATCH v9 14/22] KVM: s390: interfaces to clear CRYCB masks

On 08/15/2018 09:10 AM, Cornelia Huck wrote:
> On Mon, 13 Aug 2018 17:48:11 -0400
> Tony Krowiak <akrowiak@...ux.vnet.ibm.com> wrote:
>
>> From: Tony Krowiak <akrowiak@...ux.ibm.com>
>>
>> Introduces two new KVM interface to clear the APM, AQM and ADM masks in
>> the guest's CRYCB.  The VCPUs are taken out of SIE to ensure the VCPUs do
>> not get out of sync.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
>> Acked-by: Halil Pasic <pasic@...ux.ibm.com>
>> Tested-by: Michael Mueller <mimu@...ux.ibm.com>
>> Tested-by: Farhan Ali <alifm@...ux.ibm.com>
>> Tested-by: Pierre Morel <pmorel@...ux.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h |    3 +++
>>   arch/s390/kvm/kvm-s390.c         |   15 +++++++++++++++
>>   2 files changed, 18 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index 4a739d4..07e58d8 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -258,6 +258,7 @@ struct kvm_s390_sie_block {
>>   	__u64	tecmc;			/* 0x00e8 */
>>   	__u8	reservedf0[12];		/* 0x00f0 */
>>   #define CRYCB_FORMAT_MASK 0x00000003
>> +#define CRYCB_FORMAT0 0x00000000
> This should probably go into a different patch (define is not used
> here)?

You are spot on. It needs to go in patch 15 where it is first used.

>
>>   #define CRYCB_FORMAT1 0x00000001
>>   #define CRYCB_FORMAT2 0x00000003
>>   	__u32	crycbd;			/* 0x00fc */
>> @@ -861,6 +862,8 @@ void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
>>   void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
>>   				 struct kvm_async_pf *work);
>>   
>> +void kvm_arch_crypto_clear_masks(struct kvm *kvm);
>> +
>>   extern int sie64a(struct kvm_s390_sie_block *, u64 *);
>>   extern char sie_exit;
>>   
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index f7de123..8d8a65a 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -1919,6 +1919,21 @@ static void kvm_s390_set_crycb_format(struct kvm *kvm)
>>   		kvm->arch.crypto.crycbd |= CRYCB_FORMAT1;
>>   }
>>   
>> +void kvm_arch_crypto_clear_masks(struct kvm *kvm)
>> +{
>> +	mutex_lock(&kvm->lock);
>> +	kvm_s390_vcpu_block_all(kvm);
>> +
>> +	memset(&kvm->arch.crypto.crycb->apcb0, 0,
>> +	       sizeof(kvm->arch.crypto.crycb->apcb0));
>> +	memset(&kvm->arch.crypto.crycb->apcb1, 0,
>> +	       sizeof(kvm->arch.crypto.crycb->apcb1));
>> +
>> +	kvm_s390_vcpu_unblock_all(kvm);
>> +	mutex_unlock(&kvm->lock);
>> +}
>> +EXPORT_SYMBOL(kvm_arch_crypto_clear_masks);
> A quick grep shows that kvm-related exports tend to be
> EXPORT_SYMBOL_GPL. Should that also be done here?

I did some internet searching to find out why the EXPORT_SYMBOL_GPL 
macro is used
rather than EXPORT_SYMBOL. I found the link below which explains why. 
According to
that article, if the EXPORT_SYMBOL_GPL macro is used, modules that do 
not carry a
GPL-compatible license can not use the function. Apparently Linus 
Trovalds and the
lawyers he consulted believe it codifies the intention in code itself 
makes the code
more flexible and a lot less likely to be misunderstood. It is further 
pointed out
that "circumventing the GPL-only export requires an explicit action, 
making it clear
that the copyright infringement was a  deliberate act.

Since our modules are GPL-licensed, it would probably behoove us to use the
EXPORT_SYMBOL_GPL macro to export this function.

https://lwn.net/Articles/154602/

>
>> +
>>   static u64 kvm_s390_get_initial_cpuid(void)
>>   {
>>   	struct cpuid cpuid;