Re: [PATCH 2/2] KVM: s390: Add storage key facility interpretation control

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On 02/16/2018 03:46 PM, David Hildenbrand wrote:
> On 16.02.2018 15:35, Janosch Frank wrote:
>> On 16.02.2018 15:30, David Hildenbrand wrote:
>>> On 16.02.2018 12:16, Janosch Frank wrote:
>>>> Up to now we always expected to have the storage key facility
>>>> available for our (non-VSIE) KVM guests. For huge page support, we
>>>> need to be able to disable it, so let's introduce that now.
>>>>
>>>> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx>
>>>> Reviewed-by: Farhan Ali <alifm@xxxxxxxxxxxxxxxxxx>
>>>> ---
>>>>  arch/s390/include/asm/kvm_host.h    |  1 +
>>>>  arch/s390/include/asm/mmu.h         |  2 +-
>>>>  arch/s390/include/asm/mmu_context.h |  2 +-
>>>>  arch/s390/include/asm/pgtable.h     |  4 ++--
>>>>  arch/s390/kvm/kvm-s390.c            |  3 ++-
>>>>  arch/s390/kvm/priv.c                | 22 +++++++++++++---------
>>>>  arch/s390/mm/gmap.c                 |  6 +++---
>>>>  arch/s390/mm/pgtable.c              |  4 ++--
>>>>  8 files changed, 25 insertions(+), 19 deletions(-)
>>>>
>>>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>>>> index 27918b1..f161ad0 100644
>>>> --- a/arch/s390/include/asm/kvm_host.h
>>>> +++ b/arch/s390/include/asm/kvm_host.h
>>>> @@ -793,6 +793,7 @@ struct kvm_arch{
>>>>  	int use_irqchip;
>>>>  	int use_cmma;
>>>>  	int use_pfmfi;
>>>> +	int use_skf;
>>>>  	int user_cpu_state_ctrl;
>>>>  	int user_sigp;
>>>>  	int user_stsi;
>>>> diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h
>>>> index c639c95..f5ff9db 100644
>>>> --- a/arch/s390/include/asm/mmu.h
>>>> +++ b/arch/s390/include/asm/mmu.h
>>>> @@ -21,7 +21,7 @@ typedef struct {
>>>>  	/* The mmu context uses extended page tables. */
>>>>  	unsigned int has_pgste:1;
>>>>  	/* The mmu context uses storage keys. */
>>>> -	unsigned int use_skey:1;
>>>> +	unsigned int uses_skeys:1;
>>>>  	/* The mmu context uses CMM. */
>>>>  	unsigned int uses_cmm:1;
>>>>  } mm_context_t;
>>>> diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
>>>> index d3ebfa8..bc9a2a9 100644
>>>> --- a/arch/s390/include/asm/mmu_context.h
>>>> +++ b/arch/s390/include/asm/mmu_context.h
>>>> @@ -30,7 +30,7 @@ static inline int init_new_context(struct task_struct *tsk,
>>>>  		test_thread_flag(TIF_PGSTE) ||
>>>>  		(current->mm && current->mm->context.alloc_pgste);
>>>>  	mm->context.has_pgste = 0;
>>>> -	mm->context.use_skey = 0;
>>>> +	mm->context.uses_skeys = 0;
>>>>  	mm->context.uses_cmm = 0;
>>>>  #endif
>>>>  	switch (mm->context.asce_limit) {
>>>> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
>>>> index 9223b4d..4f26425 100644
>>>> --- a/arch/s390/include/asm/pgtable.h
>>>> +++ b/arch/s390/include/asm/pgtable.h
>>>> @@ -509,10 +509,10 @@ static inline int mm_alloc_pgste(struct mm_struct *mm)
>>>>   * faults should no longer be backed by zero pages
>>>>   */
>>>>  #define mm_forbids_zeropage mm_has_pgste
>>>> -static inline int mm_use_skey(struct mm_struct *mm)
>>>> +static inline int mm_uses_skeys(struct mm_struct *mm)
>>>>  {
>>>>  #ifdef CONFIG_PGSTE
>>>> -	if (mm->context.use_skey)
>>>> +	if (mm->context.uses_skeys)
>>>>  		return 1;
>>>>  #endif
>>>>  	return 0;
>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>> index 8fb6549..90deb7b 100644
>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>> @@ -1432,7 +1432,7 @@ static long kvm_s390_get_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
>>>>  		return -EINVAL;
>>>>  
>>>>  	/* Is this guest using storage keys? */
>>>> -	if (!mm_use_skey(current->mm))
>>>> +	if (!mm_uses_skeys(current->mm))
>>>>  		return KVM_S390_GET_SKEYS_NONE;
>>>>  
>>>>  	/* Enforce sane limit on memory allocation */
>>>> @@ -2010,6 +2010,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>>>>  	kvm->arch.css_support = 0;
>>>>  	kvm->arch.use_irqchip = 0;
>>>>  	kvm->arch.use_pfmfi = sclp.has_pfmfi;
>>>> +	kvm->arch.use_skf = sclp.has_skey;
>>>>  	kvm->arch.epoch = 0;
>>>>  
>>>>  	spin_lock_init(&kvm->arch.start_stop_lock);
>>>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
>>>> index 76a2380..d9bd147 100644
>>>> --- a/arch/s390/kvm/priv.c
>>>> +++ b/arch/s390/kvm/priv.c
>>>> @@ -208,19 +208,23 @@ int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu)
>>>>  	struct kvm_s390_sie_block *sie_block = vcpu->arch.sie_block;
>>>>  
>>>>  	trace_kvm_s390_skey_related_inst(vcpu);
>>>> -	if (!(sie_block->ictl & (ICTL_ISKE | ICTL_SSKE | ICTL_RRBE)) &&
>>>> +	/* Already enabled? */
>>>> +	if (vcpu->kvm->arch.use_skf &&
>>>> +	    !(sie_block->ictl & (ICTL_ISKE | ICTL_SSKE | ICTL_RRBE)) &&
>>>>  	    !kvm_s390_test_cpuflags(vcpu, CPUSTAT_KSS))
>>>>  		return rc;
>>>
>>> While at it, can you directly "return 0;" here and remove the
>>> initialization of rc to 0? Makes the code easier to read
>>
>> Sure
>>
>>>
>>>>  
>>>>  	rc = s390_enable_skey();
>>>>  	VCPU_EVENT(vcpu, 3, "enabling storage keys for guest: %d", rc);
>>>> -	if (!rc) {
>>>> -		if (kvm_s390_test_cpuflags(vcpu, CPUSTAT_KSS))
>>>> -			kvm_s390_clear_cpuflags(vcpu, CPUSTAT_KSS);
>>>> -		else
>>>> -			sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE |
>>>> -					     ICTL_RRBE);
>>>> -	}
>>>> +	if (rc)
>>>> +		return rc;
>>>> +
>>>> +	if (kvm_s390_test_cpuflags(vcpu, CPUSTAT_KSS))
>>>> +		kvm_s390_clear_cpuflags(vcpu, CPUSTAT_KSS);
>>>> +	if (!vcpu->kvm->arch.use_skf)
>>>> +		sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
>>>> +	else
>>>> +		sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE | ICTL_RRBE);
>>>
>>>
>>> I wonder why
>>>
>>> vcpu->arch.sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
>>>
>>> Is set conditionally (sclp.has_kss) in kvm_arch_vcpu_setup().
>>>
>>> Can't we simply always set these bits there and only clear them here
>>> conditionally?
>>
>> Intercept priority... skey intercepts are more important than kss.
>>
> 
> ... but does that make any difference here?

The priority makes a difference for vsie. I think it makes sense to 
keep this is sync (e.g. if everybody has kss, really use kss and not
the ictl variants).




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