From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH v4 2/2] s390/kvm: diagnose 318 handling References: <1556751063-21835-1-git-send-email-walling@linux.ibm.com> <1556751063-21835-3-git-send-email-walling@linux.ibm.com> <783ecdb4-3bc2-4bf3-55cb-9a902467aadd@redhat.com> From: Collin Walling Date: Thu, 2 May 2019 11:25:28 -0400 MIME-Version: 1.0 In-Reply-To: <783ecdb4-3bc2-4bf3-55cb-9a902467aadd@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <1988b4c3-e123-47dd-2008-15d8bec0171d@linux.ibm.com> Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: David Hildenbrand , cohuck@redhat.com, pbonzini@redhat.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org List-ID: On 5/2/19 8:59 AM, David Hildenbrand wrote: > On 02.05.19 00:51, Collin Walling wrote: >> DIAGNOSE 0x318 (diag318) is a privileged s390x instruction that must >> be intercepted by SIE and handled via KVM. Let's introduce some >> functions to communicate between userspace and KVM via ioctls. These >> will be used to get/set the diag318 related information (also known >> as the "Control Program Code" or "CPC"), as well as check the system >> if KVM supports handling this instruction. >> >> This information can help with diagnosing the OS the VM is running >> in (Linux, z/VM, etc) if the OS calls this instruction. >> >> The get/set functions are introduced primarily for VM migration and >> reset, though no harm could be done to the system if a userspace >> program decides to alter this data (this is highly discouraged). >> >> The Control Program Name Code (CPNC) is stored in the SIE block and >> a copy is retained in each VCPU. The Control Program Version Code >> (CPVC) retains a copy in each VCPU as well. >> >> At this time, the CPVC is not reported as its format is yet to be >> defined. >> >> Note that the CPNC is set in the SIE block iff the host hardware >> supports it. > > For vSIE and SIE you only configure the CPNC. Is that sufficient? > Shouldn't diag318 allow the guest to set both? (especially regarding vSIE) > The SIE block only stores the CPNC. The CPVC is not designed to be stored in the SIE block, so we store it in guest memory only. > [...] >> >> diff --git a/Documentation/virtual/kvm/devices/vm.txt b/Documentation/virtual/kvm/devices/vm.txt >> index 95ca68d..9a8d934 100644 >> --- a/Documentation/virtual/kvm/devices/vm.txt >> +++ b/Documentation/virtual/kvm/devices/vm.txt >> @@ -267,3 +267,17 @@ Parameters: address of a buffer in user space to store the data (u64) to; >> if it is enabled >> Returns: -EFAULT if the given address is not accessible from kernel space >> 0 in case of success. >> + >> +6. GROUP: KVM_S390_VM_MISC >> +Architectures: s390 >> + >> +6.1. KVM_S390_VM_MISC_CPC (r/w) >> + >> +Allows userspace to access the "Control Program Code" which consists of a >> +1-byte "Control Program Name Code" and a 7-byte "Control Program Version Code". >> +This information is initialized during IPL and must be preserved during >> +migration. > > Your implementation does not match this description. User space can only > get/set the cpnc effectively for the HW to see it, not the CPVC, no? > We retrieve the entire CPNC + CPVC. User space (i.e. QEMU) can retrieve this 64-bit value and save / load it during live guest migration. I figured it would be best to set / get this entire value now, so that we don't need to add extra handling for the version code later when its format is properly decided. > Shouldn't you transparently forward that data to the SCB for vSIE/SIE, > because we really don't care what the target format will be? > Sorry, I'm not fully understanding what you mean by "we really don't care what the target format will be?" Do you mean to shadow the CPNC without checking if diag318 is supported? I imagine that would be harmless. >> + >> +Parameters: address of a buffer in user space to store the data (u64) to >> +Returns: -EFAULT if the given address is not accessible from kernel space >> + 0 in case of success. > > [...] >> >> #define KVM_HVA_ERR_BAD (-1UL) >> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h >> index 16511d9..3d3d2a5 100644 >> --- a/arch/s390/include/uapi/asm/kvm.h >> +++ b/arch/s390/include/uapi/asm/kvm.h >> @@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req { >> #define KVM_S390_VM_CRYPTO 2 >> #define KVM_S390_VM_CPU_MODEL 3 >> #define KVM_S390_VM_MIGRATION 4 >> +#define KVM_S390_VM_MISC 5 >> >> /* kvm attributes for mem_ctrl */ >> #define KVM_S390_VM_MEM_ENABLE_CMMA 0 >> @@ -168,6 +169,9 @@ struct kvm_s390_vm_cpu_subfunc { >> #define KVM_S390_VM_MIGRATION_START 1 >> #define KVM_S390_VM_MIGRATION_STATUS 2 >> >> +/* kvm attributes for KVM_S390_VM_MISC */ >> +#define KVM_S390_VM_MISC_CPC 0 >> + >> /* for KVM_GET_REGS and KVM_SET_REGS */ >> struct kvm_regs { >> /* general purpose regs for s390 */ >> diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c >> index 45634b3d..9762e6a 100644 >> --- a/arch/s390/kvm/diag.c >> +++ b/arch/s390/kvm/diag.c >> @@ -235,6 +235,21 @@ static int __diag_virtio_hypercall(struct kvm_vcpu *vcpu) >> return ret < 0 ? ret : 0; >> } >> >> +static int __diag_set_control_prog_name(struct kvm_vcpu *vcpu) > > Can we name that "__diag_set_cpc" ? > > "control_prog_name" is certainly not 100% correct. > Sure >> +{ >> + unsigned int reg = (vcpu->arch.sie_block->ipa & 0xf0) >> 4; >> + u64 cpc = vcpu->run->s.regs.gprs[reg]; >> + >> + vcpu->stat.diagnose_318++; >> + kvm_s390_set_cpc(vcpu->kvm, cpc); >> + >> + VCPU_EVENT(vcpu, 3, "diag 0x318 cpnc: 0x%x cpvc: 0x%llx", >> + vcpu->kvm->arch.diag318_info.cpnc, >> + (u64)vcpu->kvm->arch.diag318_info.cpvc); >> + >> + return 0; >> +} > > > [...] >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index 4638303..910af18 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -156,6 +156,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = { >> { "instruction_diag_9c", VCPU_STAT(diagnose_9c) }, >> { "instruction_diag_258", VCPU_STAT(diagnose_258) }, >> { "instruction_diag_308", VCPU_STAT(diagnose_308) }, >> + { "instruction_diag_318", VCPU_STAT(diagnose_318) }, >> { "instruction_diag_500", VCPU_STAT(diagnose_500) }, >> { "instruction_diag_other", VCPU_STAT(diagnose_other) }, >> { NULL } >> @@ -1190,6 +1191,70 @@ static int kvm_s390_get_tod(struct kvm *kvm, struct kvm_device_attr *attr) >> return ret; >> } >> >> +void kvm_s390_set_cpc(struct kvm *kvm, u64 cpc) >> +{ >> + struct kvm_vcpu *vcpu; >> + int i; >> + >> + mutex_lock(&kvm->lock); >> + kvm->arch.diag318_info.val = cpc; >> + >> + VM_EVENT(kvm, 3, "SET: CPNC: 0x%x CPVC: 0x%llx", >> + kvm->arch.diag318_info.cpnc, (u64)kvm->arch.diag318_info.cpvc); >> + >> + if (sclp.has_diag318) { >> + kvm_for_each_vcpu(i, vcpu, kvm) { >> + vcpu->arch.sie_block->cpnc = kvm->arch.diag318_info.cpnc; >> + } >> + } > > Do we care about races here between guest VCPUs reading it via the SCB > (HW) and us changing the value? My gut feeling is that it can be tolerated. > >> + mutex_unlock(&kvm->lock); >> +} >> + >> +static int kvm_s390_set_misc(struct kvm *kvm, struct kvm_device_attr *attr) >> +{ >> + int ret; >> + u64 cpc; >> + >> + switch (attr->attr) { >> + case KVM_S390_VM_MISC_CPC: >> + ret = -EFAULT; >> + if (get_user(cpc, (u64 __user *)attr->addr)) >> + break; >> + kvm_s390_set_cpc(kvm, cpc); >> + ret = 0; >> + break; >> + default: >> + ret = -ENXIO; >> + break; >> + } >> + return ret; >> +} >> + >> +static int kvm_s390_get_cpc(struct kvm *kvm, struct kvm_device_attr *attr) >> +{ >> + if (put_user(kvm->arch.diag318_info.val, (u64 __user *)attr->addr)) >> + return -EFAULT; > > Another possible race with setting code. Should be at least take the > kvm->lock here? Otherwise, also looks like this can be tolerated. > I'm 99% sure both can be tolerated. I can't really think of a scenario where not taking the lock in either get / set would cause any concerns. Thanks for the review!