Re: [PATCH RFC 2/6] KVM: s390: provide only a single function for setting the tod

["Collin L. Walling" <walling@linux.vnet.ibm.com>]

On 02/07/2018 06:46 AM, David Hildenbrand wrote:
> Right now, SET CLOCK called in the guest does not properly take care of
> the epoch index, as the call goes via the old kvm_s390_set_tod_clock()
> interface. So the epoch index is neither reset to 0, if required, nor
> properly set to e.g. 0xff on negative values.
>
> Fix this by providing a single kvm_s390_set_tod_clock() function. Move
> Multiple-epoch facility handling into it.
>
> Signed-off-by: David Hildenbrand<david@redhat.com>
> ---
>   arch/s390/kvm/kvm-s390.c | 46 +++++++++++++++-------------------------------
>   arch/s390/kvm/kvm-s390.h |  5 ++---
>   arch/s390/kvm/priv.c     |  9 +++++----
>   3 files changed, 22 insertions(+), 38 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index ba4c7092335a..b514ee427077 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -902,12 +902,9 @@ static int kvm_s390_set_tod_ext(struct kvm *kvm, struct kvm_device_attr *attr)
>   	if (copy_from_user(&gtod, (void __user *)attr->addr, sizeof(gtod)))
>   		return -EFAULT;
>
> -	if (test_kvm_facility(kvm, 139))
> -		kvm_s390_set_tod_clock_ext(kvm, &gtod);
> -	else if (gtod.epoch_idx == 0)
> -		kvm_s390_set_tod_clock(kvm, gtod.tod);
> -	else
> +	if (!test_kvm_facility(kvm, 139) && gtod.epoch_idx)
>   		return -EINVAL;
> +	kvm_s390_set_tod_clock(kvm, &gtod);
>
>   	VM_EVENT(kvm, 3, "SET: TOD extension: 0x%x, TOD base: 0x%llx",
>   		gtod.epoch_idx, gtod.tod);
> @@ -932,13 +929,14 @@ static int kvm_s390_set_tod_high(struct kvm *kvm, struct kvm_device_attr *attr)
>
>   static int kvm_s390_set_tod_low(struct kvm *kvm, struct kvm_device_attr *attr)
>   {
> -	u64 gtod;
> +	struct kvm_s390_vm_tod_clock gtod = { 0 };
>
> -	if (copy_from_user(&gtod, (void __user *)attr->addr, sizeof(gtod)))
> +	if (copy_from_user(&gtod.tod, (void __user *)attr->addr,
> +			   sizeof(gtod.tod)))
>   		return -EFAULT;
>
> -	kvm_s390_set_tod_clock(kvm, gtod);
> -	VM_EVENT(kvm, 3, "SET: TOD base: 0x%llx", gtod);
> +	kvm_s390_set_tod_clock(kvm, &gtod);
> +	VM_EVENT(kvm, 3, "SET: TOD base: 0x%llx", gtod.tod);
>   	return 0;
>   }
>
> @@ -3021,8 +3019,8 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
>   	return 0;
>   }
>
> -void kvm_s390_set_tod_clock_ext(struct kvm *kvm,
> -				 const struct kvm_s390_vm_tod_clock *gtod)
> +void kvm_s390_set_tod_clock(struct kvm *kvm,
> +			    const struct kvm_s390_vm_tod_clock *gtod)
Nit: off by one space --------^

>   {
>   	struct kvm_vcpu *vcpu;
>   	struct kvm_s390_tod_clock_ext htod;
> @@ -3034,10 +3032,12 @@ void kvm_s390_set_tod_clock_ext(struct kvm *kvm,
>   	get_tod_clock_ext((char *)&htod);
>
>   	kvm->arch.epoch = gtod->tod - htod.tod;
> -	kvm->arch.epdx = gtod->epoch_idx - htod.epoch_idx;
> -
> -	if (kvm->arch.epoch > gtod->tod)
> -		kvm->arch.epdx -= 1;
> +	kvm->arch.epdx = 0;
> +	if (test_kvm_facility(kvm, 139)) {
> +		kvm->arch.epdx = gtod->epoch_idx - htod.epoch_idx;
> +		if (kvm->arch.epoch > gtod->tod)
> +			kvm->arch.epdx -= 1;
> +	}
>
>   	kvm_s390_vcpu_block_all(kvm);
>   	kvm_for_each_vcpu(i, vcpu, kvm) {
> @@ -3050,22 +3050,6 @@ void kvm_s390_set_tod_clock_ext(struct kvm *kvm,
>   	mutex_unlock(&kvm->lock);
>   }
>
> -void kvm_s390_set_tod_clock(struct kvm *kvm, u64 tod)
> -{
> -	struct kvm_vcpu *vcpu;
> -	int i;
> -
> -	mutex_lock(&kvm->lock);
> -	preempt_disable();
> -	kvm->arch.epoch = tod - get_tod_clock();
> -	kvm_s390_vcpu_block_all(kvm);
> -	kvm_for_each_vcpu(i, vcpu, kvm)
> -		vcpu->arch.sie_block->epoch = kvm->arch.epoch;
> -	kvm_s390_vcpu_unblock_all(kvm);
> -	preempt_enable();
> -	mutex_unlock(&kvm->lock);
> -}
> -
>   /**
>    * kvm_arch_fault_in_page - fault-in guest page if necessary
>    * @vcpu: The corresponding virtual cpu
> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
> index bd31b37b0e6f..19d719262765 100644
> --- a/arch/s390/kvm/kvm-s390.h
> +++ b/arch/s390/kvm/kvm-s390.h
> @@ -283,9 +283,8 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu);
>   int kvm_s390_handle_sigp_pei(struct kvm_vcpu *vcpu);
>
>   /* implemented in kvm-s390.c */
> -void kvm_s390_set_tod_clock_ext(struct kvm *kvm,
> -				 const struct kvm_s390_vm_tod_clock *gtod);
> -void kvm_s390_set_tod_clock(struct kvm *kvm, u64 tod);
> +void kvm_s390_set_tod_clock(struct kvm *kvm,
> +			    const struct kvm_s390_vm_tod_clock *gtod);
Same nit here.
>   long kvm_arch_fault_in_page(struct kvm_vcpu *vcpu, gpa_t gpa, int writable);
>   int kvm_s390_store_status_unloaded(struct kvm_vcpu *vcpu, unsigned long addr);
>   int kvm_s390_vcpu_store_status(struct kvm_vcpu *vcpu, unsigned long addr);
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index c4c4e157c036..33505c32c48a 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -85,9 +85,10 @@ int kvm_s390_handle_e3(struct kvm_vcpu *vcpu)
>   /* Handle SCK (SET CLOCK) interception */
>   static int handle_set_clock(struct kvm_vcpu *vcpu)
>   {
> +	struct kvm_s390_vm_tod_clock gtod = { 0 };
>   	int rc;
>   	u8 ar;
> -	u64 op2, val;
> +	u64 op2;
>
>   	vcpu->stat.instruction_sck++;
>
> @@ -97,12 +98,12 @@ static int handle_set_clock(struct kvm_vcpu *vcpu)
>   	op2 = kvm_s390_get_base_disp_s(vcpu, &ar);
>   	if (op2 & 7)	/* Operand must be on a doubleword boundary */
>   		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> -	rc = read_guest(vcpu, op2, ar, &val, sizeof(val));
> +	rc = read_guest(vcpu, op2, ar, &gtod.tod, sizeof(gtod.tod));
>   	if (rc)
>   		return kvm_s390_inject_prog_cond(vcpu, rc);
>
> -	VCPU_EVENT(vcpu, 3, "SCK: setting guest TOD to 0x%llx", val);
> -	kvm_s390_set_tod_clock(vcpu->kvm, val);
> +	VCPU_EVENT(vcpu, 3, "SCK: setting guest TOD to 0x%llx", gtod.tod);
> +	kvm_s390_set_tod_clock(vcpu->kvm, &gtod);
>
>   	kvm_s390_set_psw_cc(vcpu, 0);
>   	return 0;
Set clock only concerns the left-most 64 bits of the TOD-Clock, right? 
(thinking out
loud) I wonder if we need to also concern ourselves about the epoch 
extension... but
perhaps current use cases of set clock do not warrant that?

-- 
- Collin L Walling