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

[Tony Krowiak]

On 08/15/2018 09:10 AM, Cornelia Huck wrote:
> On Mon, 13 Aug 2018 17:48:11 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx> wrote:
>
> > From: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxx>
> > Acked-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
> > Tested-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
> > Tested-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> > Tested-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > ---
> >   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;