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

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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?


-- 

Thanks,

David / dhildenb



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