Re: [PATCH/RFC 5/9] KVM: s390: introduce post handlers for STSI

[Paolo Bonzini <pbonzini@redhat.com>]

On 16/03/2015 09:51, Christian Borntraeger wrote:
> From: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
> 
> The Store System Information (STSI) instruction currently collects all
> information it relays to the caller in the kernel. Some information,
> however, is only available in user space. An example of this is the
> guest name: The kernel always sets "KVMGuest", but user space knows the
> actual guest name.
> 
> This patch introduces a new exit, KVM_EXIT_S390_STSI, guarded by a
> capability that can be enabled by user space if it wants to be able to
> insert such data. User space will be provided with the target buffer
> and the requested STSI function code.
> 
> Reviewed-by: Eric Farman <farman@linux.vnet.ibm.com>
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
>  Documentation/virtual/kvm/api.txt | 28 ++++++++++++++++++++++++++++
>  arch/s390/include/asm/kvm_host.h  |  1 +
>  arch/s390/kvm/kvm-s390.c          |  5 +++++
>  arch/s390/kvm/priv.c              | 16 +++++++++++++++-
>  include/uapi/linux/kvm.h          | 11 +++++++++++
>  5 files changed, 60 insertions(+), 1 deletion(-)

This is okay, but it made me curious about s390 specifics because it's
different from the x86 equivalent.  The x86 info is always 16-byte (4
times 32 bit) and the selectors are few (roughly 30), and it is passed
to the kernel at init time via KVM_SET_CPUID2.  How many selectors are
there on s390, and how big is the info that can be written?

Paolo

> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index f03178d..74d18b6 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3304,3 +3304,31 @@ Returns: 0 on success, negative value on error
>  Allows use of the vector registers introduced with z13 processor, and
>  provides for the synchronization between host and user space.  Will
>  return -EINVAL if the machine does not support vectors.
> +
> +7.4 KVM_CAP_S390_USER_STSI
> +
> +Architectures: s390
> +Parameters: none
> +
> +This capability allows post-handlers for the STSI instruction. After
> +initial handling in the kernel, KVM exits to user space with
> +KVM_EXIT_S390_STSI to allow user space to insert further data.
> +
> +Before exiting to userspace, kvm handlers should fill in s390_stsi field of
> +vcpu->run:
> +struct {
> +	__u64 addr;
> +	__u8 ar;
> +	__u8 reserved;
> +	__u8 fc;
> +	__u8 sel1;
> +	__u16 sel2;
> +} s390_stsi;
> +
> +@addr - guest address of STSI SYSIB
> +@fc   - function code
> +@sel1 - selector 1
> +@sel2 - selector 2
> +@ar   - access register number
> +
> +KVM handlers should exit to userspace with rc = -EREMOTE.
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 347a333..2356a8c 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -565,6 +565,7 @@ struct kvm_arch{
>  	int use_vectors;
>  	int user_cpu_state_ctrl;
>  	int user_sigp;
> +	int user_stsi;
>  	struct s390_io_adapter *adapters[MAX_S390_IO_ADAPTERS];
>  	wait_queue_head_t ipte_wq;
>  	int ipte_lock_count;
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 92855e2..1f5baf4 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -178,6 +178,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_VM_ATTRIBUTES:
>  	case KVM_CAP_MP_STATE:
>  	case KVM_CAP_S390_USER_SIGP:
> +	case KVM_CAP_S390_USER_STSI:
>  		r = 1;
>  		break;
>  	case KVM_CAP_S390_MEM_OP:
> @@ -280,6 +281,10 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>  		kvm->arch.use_vectors = MACHINE_HAS_VX;
>  		r = MACHINE_HAS_VX ? 0 : -EINVAL;
>  		break;
> +	case KVM_CAP_S390_USER_STSI:
> +		kvm->arch.user_stsi = 1;
> +		r = 0;
> +		break;
>  	default:
>  		r = -EINVAL;
>  		break;
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 5f26425..211102c 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -488,6 +488,16 @@ static void handle_stsi_3_2_2(struct kvm_vcpu *vcpu, struct sysinfo_3_2_2 *mem)
>  	ASCEBC(mem->vm[0].cpi, 16);
>  }
>  
> +static void insert_stsi_usr_data(struct kvm_vcpu *vcpu, u64 addr, u8 fc,
> +				 u8 sel1, u16 sel2)
> +{
> +	vcpu->run->exit_reason = KVM_EXIT_S390_STSI;
> +	vcpu->run->s390_stsi.addr = addr;
> +	vcpu->run->s390_stsi.fc = fc;
> +	vcpu->run->s390_stsi.sel1 = sel1;
> +	vcpu->run->s390_stsi.sel2 = sel2;
> +}
> +
>  static int handle_stsi(struct kvm_vcpu *vcpu)
>  {
>  	int fc = (vcpu->run->s.regs.gprs[0] & 0xf0000000) >> 28;
> @@ -547,11 +557,15 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
>  		rc = kvm_s390_inject_prog_cond(vcpu, rc);
>  		goto out;
>  	}
> +	if (vcpu->kvm->arch.user_stsi) {
> +		insert_stsi_usr_data(vcpu, operand2, fc, sel1, sel2);
> +		rc = -EREMOTE;
> +	}
>  	trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2);
>  	free_page(mem);
>  	kvm_s390_set_psw_cc(vcpu, 0);
>  	vcpu->run->s.regs.gprs[0] = 0;
> -	return 0;
> +	return rc;
>  out_no_data:
>  	kvm_s390_set_psw_cc(vcpu, 3);
>  out:
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 74bbd9a..279ffd2 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -172,6 +172,7 @@ struct kvm_pit_config {
>  #define KVM_EXIT_S390_TSCH        22
>  #define KVM_EXIT_EPR              23
>  #define KVM_EXIT_SYSTEM_EVENT     24
> +#define KVM_EXIT_S390_STSI        25
>  
>  /* For KVM_EXIT_INTERNAL_ERROR */
>  /* Emulate instruction failed. */
> @@ -309,6 +310,15 @@ struct kvm_run {
>  			__u32 type;
>  			__u64 flags;
>  		} system_event;
> +		/* KVM_EXIT_S390_STSI */
> +		struct {
> +			__u64 addr;
> +			__u8 ar;
> +			__u8 reserved;
> +			__u8 fc;
> +			__u8 sel1;
> +			__u16 sel2;
> +		} s390_stsi;
>  		/* Fix the size of the union. */
>  		char padding[256];
>  	};
> @@ -780,6 +790,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_S390_USER_SIGP 106
>  #define KVM_CAP_S390_VECTOR_REGISTERS 107
>  #define KVM_CAP_S390_MEM_OP 108
> +#define KVM_CAP_S390_USER_STSI 109
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
>