Re: [PATCH 5/6] KVM: s390: wire up seb feature

Christian Borntraeger
2018-01-17T11:39:21Z

On 01/17/2018 12:33 PM, David Hildenbrand wrote:
>
>> #define ECB_GS 0x40
>> #define ECB_TE 0x10
>> #define ECB_SRSI 0x04
>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>> index 38535a57..20b9e9f 100644
>> --- a/arch/s390/include/uapi/asm/kvm.h
>> +++ b/arch/s390/include/uapi/asm/kvm.h
>> @@ -224,6 +224,7 @@ struct kvm_guest_debug_arch {
>> #define KVM_SYNC_RICCB (1UL << 7)
>> #define KVM_SYNC_FPRS (1UL << 8)
>> #define KVM_SYNC_GSCB (1UL << 9)
>> +#define KVM_SYNC_SEBC (1UL << 10)
>> /* length and alignment of the sdnx as a power of two */
>> #define SDNXC 8
>> #define SDNXL (1UL << SDNXC)
>> @@ -247,7 +248,8 @@ struct kvm_sync_regs {
>> };
>> __u8 reserved[512]; /* for future vector expansion */
>> __u32 fpc; /* valid on KVM_SYNC_VRS or KVM_SYNC_FPRS */
>> - __u8 padding1[52]; /* riccb needs to be 64byte aligned */
>> + __u8 sebc:1; /* spec blocking */
>
> do you want to define the unused bits as reserved? Nicer to read IMHO

I certainly want to have these bits for future use. So maybe a
__u8 reserved : 7;
after that makes a lot of sense. Also the sebc : 1; (spaces)

(FWIW, I will rename that to bpbc for other reasons).

>
> (especially also using spaces "sebc : 1")
>
>> + __u8 padding1[51]; /* riccb needs to be 64byte aligned */
>> __u8 riccb[64]; /* runtime instrumentation controls block */
>> __u8 padding2[192]; /* sdnx needs to be 256byte aligned */
>> union {
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 2c93cbb..0c18f73 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -421,6 +421,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> case KVM_CAP_S390_GS:
>> r = test_facility(133);
>> break;
>> + case KVM_CAP_S390_SEB:
>> + r = test_facility(82);
>> + break;
>> default:
>> r = 0;
>> }
>> @@ -2198,6 +2201,8 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
>> kvm_s390_set_prefix(vcpu, 0);
>> if (test_kvm_facility(vcpu->kvm, 64))
>> vcpu->run->kvm_valid_regs |= KVM_SYNC_RICCB;
>> + if (test_kvm_facility(vcpu->kvm, 82))
>> + vcpu->run->kvm_valid_regs |= KVM_SYNC_SEBC;
>> if (test_kvm_facility(vcpu->kvm, 133))
>> vcpu->run->kvm_valid_regs |= KVM_SYNC_GSCB;
>> /* fprs can be synchronized via vrs, even if the guest has no vx. With
>> @@ -2339,6 +2344,7 @@ static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
>> current->thread.fpu.fpc = 0;
>> vcpu->arch.sie_block->gbea = 1;
>> vcpu->arch.sie_block->pp = 0;
>> + vcpu->arch.sie_block->fpf &= ~FPF_SEBC;
>> 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))
>> @@ -3298,6 +3304,10 @@ static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>> vcpu->arch.sie_block->ecd |= ECD_HOSTREGMGMT;
>> vcpu->arch.gs_enabled = 1;
>> }
>> + if (kvm_run->kvm_dirty_regs & KVM_SYNC_SEBC) {
>
> We should test for test_facility(82). Otherwise user space can enable
> undefined bits in the SCB on machines with !facility 82.

Agreed, will fix.

>
>> + vcpu->arch.sie_block->fpf &= ~FPF_SEBC;
>> + vcpu->arch.sie_block->fpf |= kvm_run->s.regs.sebc ? FPF_SEBC : 0;
>> + }
>> save_access_regs(vcpu->arch.host_acrs);
>> restore_access_regs(vcpu->run->s.regs.acrs);
>> /* save host (userspace) fprs/vrs */
>> @@ -3344,6 +3354,7 @@ static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>> kvm_run->s.regs.pft = vcpu->arch.pfault_token;
>> kvm_run->s.regs.pfs = vcpu->arch.pfault_select;
>> kvm_run->s.regs.pfc = vcpu->arch.pfault_compare;
>> + kvm_run->s.regs.sebc = (vcpu->arch.sie_block->fpf & FPF_SEBC) == FPF_SEBC;
>> save_access_regs(vcpu->run->s.regs.acrs);
>> restore_access_regs(vcpu->arch.host_acrs);
>> /* Save guest register state */
>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
>> index 5d6ae03..10ea208 100644
>> --- a/arch/s390/kvm/vsie.c
>> +++ b/arch/s390/kvm/vsie.c
>> @@ -223,6 +223,10 @@ static void unshadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>> memcpy(scb_o->gcr, scb_s->gcr, 128);
>> scb_o->pp = scb_s->pp;
>>
>> + /* speculative blocking */
>
> This field should only be written back with test_kvm_facility(vcpu->kvm, 82)

Agreed.

>
> (no public documentation, this looks like the SIE can modify this field?
> Triggered by which instruction?)

The instruction from patch 3.
>
>> + scb_o->fpf &= ~FPF_SEBC;
>> + scb_o->fpf |= scb_s->fpf & FPF_SEBC;
>> +
>> /* interrupt intercept */
>> switch (scb_s->icptcode) {
>> case ICPT_PROGI:
>> @@ -265,6 +269,7 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>> scb_s->ecb3 = 0;
>> scb_s->ecd = 0;
>> scb_s->fac = 0;
>> + scb_s->fpf = 0;
>>
>> rc = prepare_cpuflags(vcpu, vsie_page);
>> if (rc)
>> @@ -324,6 +329,9 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>> prefix_unmapped(vsie_page);
>> scb_s->ecb |= scb_o->ecb & ECB_TE;
>> }
>> + /* speculative blocking */
>> + if (test_kvm_facility(vcpu->kvm, 82))
>> + scb_s->fpf |= scb_o->fpf & FPF_SEBC;
>> /* SIMD */
>> if (test_kvm_facility(vcpu->kvm, 129)) {
>> scb_s->eca |= scb_o->eca & ECA_VX;
>

Thanks for the quick review.