Re: [PATCH v7] KVM: s390: Add new reset vcpu API

Christian Borntraeger
2020-01-10T13:47:22Z

On 10.01.20 13:11, Thomas Huth wrote:
> On 10/01/2020 12.45, Janosch Frank wrote:
>> The architecture states that we need to reset local IRQs for all CPU
>> resets. Because the old reset interface did not support the normal CPU
>> reset we never did that on a normal reset.
>>
>> Let's implement an interface for the missing normal and clear resets
>> and reset all local IRQs, registers and control structures as stated
>> in the architecture.
>>
>> Userspace might already reset the registers via the vcpu run struct,
>> but as we need the interface for the interrupt clearing part anyway,
>> we implement the resets fully and don't rely on userspace to reset the
>> rest.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>> ---
>> Documentation/virt/kvm/api.txt | 43 +++++++++++++
>> arch/s390/kvm/kvm-s390.c | 112 +++++++++++++++++++++++----------
>> include/uapi/linux/kvm.h | 5 ++
>> 3 files changed, 127 insertions(+), 33 deletions(-)
>>
>> diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
>> index ebb37b34dcfc..73448764f544 100644
>> --- a/Documentation/virt/kvm/api.txt
>> +++ b/Documentation/virt/kvm/api.txt
>> @@ -4168,6 +4168,42 @@ This ioctl issues an ultravisor call to terminate the secure guest,
>> unpins the VPA pages and releases all the device pages that are used to
>> track the secure pages by hypervisor.
>>
>> +4.122 KVM_S390_NORMAL_RESET
>> +
>> +Capability: KVM_CAP_S390_VCPU_RESETS
>> +Architectures: s390
>> +Type: vcpu ioctl
>> +Parameters: none
>> +Returns: 0
>> +
>> +This ioctl resets VCPU registers and control structures according to
>> +the cpu reset definition in the POP (Principles Of Operation).
>> +
>> +4.123 KVM_S390_INITIAL_RESET
>> +
>> +Capability: none
>> +Architectures: s390
>> +Type: vcpu ioctl
>> +Parameters: none
>> +Returns: 0
>> +
>> +This ioctl resets VCPU registers and control structures according to
>> +the initial cpu reset definition in the POP. However, the cpu is not
>> +put into ESA mode. This reset is a superset of the normal reset.
>> +
>> +4.124 KVM_S390_CLEAR_RESET
>> +
>> +Capability: KVM_CAP_S390_VCPU_RESETS
>> +Architectures: s390
>> +Type: vcpu ioctl
>> +Parameters: none
>> +Returns: 0
>> +
>> +This ioctl resets VCPU registers and control structures according to
>> +the clear cpu reset definition in the POP. However, the cpu is not put
>> +into ESA mode. This reset is a superset of the initial reset.
>> +
>> +
>> 5. The kvm_run structure
>> ------------------------
>>
>> @@ -5396,3 +5432,10 @@ handling by KVM (as some KVM hypercall may be mistakenly treated as TLB
>> flush hypercalls by Hyper-V) so userspace should disable KVM identification
>> in CPUID and only exposes Hyper-V identification. In this case, guest
>> thinks it's running on Hyper-V and only use Hyper-V hypercalls.
>> +
>> +8.22 KVM_CAP_S390_VCPU_RESETS
>> +
>> +Architectures: s390
>> +
>> +This capability indicates that the KVM_S390_NORMAL_RESET and
>> +KVM_S390_CLEAR_RESET ioctls are available.
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index d9e6bf3d54f0..5640f3d6f98d 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -529,6 +529,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> case KVM_CAP_S390_CMMA_MIGRATION:
>> case KVM_CAP_S390_AIS:
>> case KVM_CAP_S390_AIS_MIGRATION:
>> + case KVM_CAP_S390_VCPU_RESETS:
>> r = 1;
>> break;
>> case KVM_CAP_S390_HPAGE_1M:
>> @@ -2844,35 +2845,6 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>>
>> }
>>
>> -static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
>> -{
>> - /* this equals initial cpu reset in pop, but we don't switch to ESA */
>> - vcpu->arch.sie_block->gpsw.mask = 0UL;
>> - vcpu->arch.sie_block->gpsw.addr = 0UL;
>> - kvm_s390_set_prefix(vcpu, 0);
>> - kvm_s390_set_cpu_timer(vcpu, 0);
>> - vcpu->arch.sie_block->ckc = 0UL;
>> - vcpu->arch.sie_block->todpr = 0;
>> - memset(vcpu->arch.sie_block->gcr, 0, 16 * sizeof(__u64));
>> - vcpu->arch.sie_block->gcr[0] = CR0_UNUSED_56 |
>> - CR0_INTERRUPT_KEY_SUBMASK |
>> - CR0_MEASUREMENT_ALERT_SUBMASK;
>> - vcpu->arch.sie_block->gcr[14] = CR14_UNUSED_32 |
>> - CR14_UNUSED_33 |
>> - CR14_EXTERNAL_DAMAGE_SUBMASK;
>> - /* make sure the new fpc will be lazily loaded */
>> - save_fpu_regs();
>> - current->thread.fpu.fpc = 0;
>> - vcpu->arch.sie_block->gbea = 1;
>> - vcpu->arch.sie_block->pp = 0;
>> - vcpu->arch.sie_block->fpf &= ~FPF_BPBC;
>> - vcpu->arch.pfault_token = KVM_S390_PFAULT_TOKEN_INVALID;
>> - kvm_clear_async_pf_completion_queue(vcpu);
>> - if (!kvm_s390_user_cpu_state_ctrl(vcpu->kvm))
>> - kvm_s390_vcpu_stop(vcpu);
>> - kvm_s390_clear_local_irqs(vcpu);
>> -}
>> -
>> void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
>> {
>> mutex_lock(&vcpu->kvm->lock);
>> @@ -3287,10 +3259,75 @@ static int kvm_arch_vcpu_ioctl_set_one_reg(struct kvm_vcpu *vcpu,
>> return r;
>> }
>>
>> -static int kvm_arch_vcpu_ioctl_initial_reset(struct kvm_vcpu *vcpu)
>> +static void kvm_arch_vcpu_ioctl_normal_reset(struct kvm_vcpu *vcpu)
>> {
>> - kvm_s390_vcpu_initial_reset(vcpu);
>> - return 0;
>> + vcpu->arch.sie_block->gpsw.mask = ~PSW_MASK_RI;
>> + vcpu->arch.pfault_token = KVM_S390_PFAULT_TOKEN_INVALID;
>> + memset(vcpu->run->s.regs.riccb, 0, sizeof(vcpu->run->s.regs.riccb));
>> +
>> + kvm_clear_async_pf_completion_queue(vcpu);
>> + if (!kvm_s390_user_cpu_state_ctrl(vcpu->kvm))
>> + kvm_s390_vcpu_stop(vcpu);
>> + kvm_s390_clear_local_irqs(vcpu);
>> +}
>> +
>> +static void kvm_arch_vcpu_ioctl_initial_reset(struct kvm_vcpu *vcpu)
>> +{
>> + /* Initial reset is a superset of the normal reset */
>> + kvm_arch_vcpu_ioctl_normal_reset(vcpu);
>> +
>> + /* this equals initial cpu reset in pop, but we don't switch to ESA */
>> + vcpu->arch.sie_block->gpsw.mask = 0UL;
>> + vcpu->arch.sie_block->gpsw.addr = 0UL;
>> + kvm_s390_set_prefix(vcpu, 0);
>> + kvm_s390_set_cpu_timer(vcpu, 0);
>> + vcpu->arch.sie_block->ckc = 0UL;
>> + vcpu->arch.sie_block->todpr = 0;
>> + memset(vcpu->arch.sie_block->gcr, 0, 16 * sizeof(__u64));
>> + vcpu->arch.sie_block->gcr[0] = CR0_UNUSED_56 |
>> + CR0_INTERRUPT_KEY_SUBMASK |
>> + CR0_MEASUREMENT_ALERT_SUBMASK;
>> + vcpu->arch.sie_block->gcr[14] = CR14_UNUSED_32 |
>> + CR14_UNUSED_33 |
>> + CR14_EXTERNAL_DAMAGE_SUBMASK;
>> + /* make sure the new fpc will be lazily loaded */
>> + save_fpu_regs();
>> + current->thread.fpu.fpc = 0;
>> + vcpu->arch.sie_block->gbea = 1;
>> + vcpu->arch.sie_block->pp = 0;
>> + vcpu->arch.sie_block->fpf &= ~FPF_BPBC;
>> +}
>> +
>> +static void kvm_arch_vcpu_ioctl_clear_reset(struct kvm_vcpu *vcpu)
>> +{
>> + struct kvm_sync_regs *regs = &vcpu->run->s.regs;
>> +
>> + /* Clear reset is a superset of the initial reset */
>> + kvm_arch_vcpu_ioctl_normal_reset(vcpu);
>
> s/kvm_arch_vcpu_ioctl_normal_reset/kvm_arch_vcpu_ioctl_initial_reset/
>
>> + memset(&regs->gprs, 0, sizeof(regs->gprs));
>> + /* Will be picked up because of save_fpu_regs() in the initial reset */
>> + memset(&current->thread.fpu.vxrs, 0, sizeof(current->thread.fpu.vxrs));
>
> I'm still not 100% sure about whether current->thread.fpu.vxrs is always
> fine here? But I hope Christian can give an ACK for that...

We do not have done the sync reg call for this ioctl, so current->thread.fpu.vxrs
still points to the userspace save area and not the kvm_run structure.
I think we must memset the kvm run structure. This might also imply that the
current code for fpc is wrong and that the initial cpu reset ioctl is clearing
the wrong fpc.
Need to look at this again.