Re: [PATCH v1 1/3] x86/kvm/hyper-v: Add support for synthetic debugger capability

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Jon Doron <arilou@gmail.com> writes:

> Add support for Hyper-V synthetic debugger (syndbg) interface.
> The syndbg interface is using MSRs to emulate a way to send/recv packets
> data.
>
> The debug transport dll (kdvm/kdnet) will identify if Hyper-V is enabled
> and if it supports the synthetic debugger interface it will attempt to
> use it, instead of trying to initialize a network adapter.
>

Cc: linux-hyperv@ list where Hyper-V folks live :-) They're in charge of
'hyperv-tlfs.h' so an ACK from them will be needed.

> Signed-off-by: Jon Doron <arilou@gmail.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h |  16 +++++
>  arch/x86/include/asm/kvm_host.h    |  11 +++
>  arch/x86/kvm/hyperv.c              | 109 +++++++++++++++++++++++++++++
>  arch/x86/kvm/hyperv.h              |   5 ++
>  arch/x86/kvm/trace.h               |  22 ++++++
>  arch/x86/kvm/x86.c                 |   8 +++
>  include/uapi/linux/kvm.h           |   9 +++
>  7 files changed, 180 insertions(+)
>
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 92abc1e42bfc..8efdf974c23f 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -33,6 +33,9 @@
>  #define HYPERV_CPUID_ENLIGHTMENT_INFO		0x40000004
>  #define HYPERV_CPUID_IMPLEMENT_LIMITS		0x40000005
>  #define HYPERV_CPUID_NESTED_FEATURES		0x4000000A
> +#define HYPERV_CPUID_SYNDBG_VENDOR_AND_MAX_FUNCTIONS	0x40000080
> +#define HYPERV_CPUID_SYNDBG_INTERFACE			0x40000081
> +#define HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES	0x40000082

Out of pure curiosity, are these CPUIDs and MSRs documented somewhere?
I'm looking at TLFS v6.0 and failing to see them...

>  
>  #define HYPERV_HYPERVISOR_PRESENT_BIT		0x80000000
>  #define HYPERV_CPUID_MIN			0x40000005
> @@ -131,6 +134,8 @@
>  #define HV_FEATURE_FREQUENCY_MSRS_AVAILABLE		BIT(8)
>  /* Crash MSR available */
>  #define HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE		BIT(10)
> +/* Support for debug MSRs available */
> +#define HV_FEATURE_DEBUG_MSRS_AVAILABLE			BIT(11)
>  /* stimer Direct Mode is available */
>  #define HV_STIMER_DIRECT_MODE_AVAILABLE			BIT(19)
>  
> @@ -194,6 +199,9 @@
>  #define HV_X64_NESTED_GUEST_MAPPING_FLUSH		BIT(18)
>  #define HV_X64_NESTED_MSR_BITMAP			BIT(19)
>  
> +/* Hyper-V synthetic debugger platform capabilities */
> +#define HV_X64_SYNDBG_CAP_ALLOW_KERNEL_DEBUGGING	BIT(1)
> +
>  /* Hyper-V specific model specific registers (MSRs) */
>  
>  /* MSR used to identify the guest OS. */
> @@ -267,6 +275,14 @@
>  /* Hyper-V guest idle MSR */
>  #define HV_X64_MSR_GUEST_IDLE			0x400000F0
>  
> +/* Hyper-V Synthetic debug options MSR */
> +#define HV_X64_MSR_SYNDBG_CONTROL		0x400000F1
> +#define HV_X64_MSR_SYNDBG_STATUS		0x400000F2
> +#define HV_X64_MSR_SYNDBG_SEND_BUFFER		0x400000F3
> +#define HV_X64_MSR_SYNDBG_RECV_BUFFER		0x400000F4
> +#define HV_X64_MSR_SYNDBG_PENDING_BUFFER	0x400000F5
> +#define HV_X64_MSR_SYNDBG_OPTIONS		0x400000FF
> +
>  /* Hyper-V guest crash notification MSR's */
>  #define HV_X64_MSR_CRASH_P0			0x40000100
>  #define HV_X64_MSR_CRASH_P1			0x40000101
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 98959e8cd448..2b755174d683 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -854,6 +854,15 @@ struct kvm_apic_map {
>  	struct kvm_lapic *phys_map[];
>  };
>  
> +/* Hyper-V synthetic debugger (SynDbg)*/
> +struct kvm_hv_syndbg {
> +	u64 control;
> +	u64 status;
> +	u64 send_page;
> +	u64 recv_page;
> +	u64 pending_page;
> +};
> +
>  /* Hyper-V emulation context */
>  struct kvm_hv {
>  	struct mutex hv_lock;
> @@ -877,6 +886,8 @@ struct kvm_hv {
>  	atomic_t num_mismatched_vp_indexes;
>  
>  	struct hv_partition_assist_pg *hv_pa_pg;
> +	u64 hv_syndbg_options;
> +	struct kvm_hv_syndbg hv_syndbg;

I would've encapsulated both to struct kvm_hv_syndbg, e.g.

struct kvm_hv_syndbg {
    struct {
     u64 control;
     u64 status;
     u64 send_page;
     u64 recv_page;
     u64 pending_page;
    } control;
    u64 options;
}

To make it clear they're part of the same thing (are they?) I see you
handle HV_X64_MSR_SYNDBG_OPTIONS differently (outside of
syndbg_set_msr()).

>  };
>  
>  enum kvm_irqchip_mode {
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index a86fda7a1d03..13176ec23496 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -266,6 +266,66 @@ static int synic_set_msr(struct kvm_vcpu_hv_synic *synic,
>  	return ret;
>  }
>  
> +static int kvm_hv_syndbg_complete_userspace(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_hv *hv = &kvm->arch.hyperv;
> +
> +	if (vcpu->run->hyperv.u.syndbg.msr == HV_X64_MSR_SYNDBG_CONTROL)
> +		hv->hv_syndbg.status = vcpu->run->hyperv.u.syndbg.status;
> +	return 1;
> +}
> +
> +static void syndbg_exit(struct kvm_vcpu *vcpu, u32 msr)
> +{
> +	struct kvm_hv_syndbg *syndbg = vcpu_to_hv_syndbg(vcpu);
> +	struct kvm_vcpu_hv *hv_vcpu = &vcpu->arch.hyperv;
> +
> +	hv_vcpu->exit.type = KVM_EXIT_HYPERV_SYNDBG;
> +	hv_vcpu->exit.u.syndbg.msr = msr;
> +	hv_vcpu->exit.u.syndbg.control = syndbg->control;
> +	hv_vcpu->exit.u.syndbg.send_page = syndbg->send_page;
> +	hv_vcpu->exit.u.syndbg.recv_page = syndbg->recv_page;
> +	hv_vcpu->exit.u.syndbg.pending_page = syndbg->pending_page;
> +	vcpu->arch.complete_userspace_io =
> +			kvm_hv_syndbg_complete_userspace;
> +
> +	kvm_make_request(KVM_REQ_HV_EXIT, vcpu);

This new interface requires userspace support apparently so we can't
enable it unconditionally (userspaces which don't support it will be
very confused). You need to introduce a capability
(KVM_CAP_HYPERV_DEBUGGING?)

> +}
> +
> +static int syndbg_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> +{
> +	struct kvm_hv_syndbg *syndbg = vcpu_to_hv_syndbg(vcpu);
> +	int ret;
> +
> +	trace_kvm_hv_syndbg_set_msr(vcpu->vcpu_id, msr, data);
> +	ret = 0;
> +	switch (msr) {
> +	case HV_X64_MSR_SYNDBG_CONTROL:
> +		syndbg->control = data;
> +		syndbg_exit(vcpu, msr);
> +		break;
> +	case HV_X64_MSR_SYNDBG_STATUS:
> +		syndbg->status = data;
> +		break;
> +	case HV_X64_MSR_SYNDBG_SEND_BUFFER:
> +		syndbg->send_page = data;
> +		break;
> +	case HV_X64_MSR_SYNDBG_RECV_BUFFER:
> +		syndbg->recv_page = data;
> +		break;
> +	case HV_X64_MSR_SYNDBG_PENDING_BUFFER:
> +		syndbg->pending_page = data;
> +		syndbg_exit(vcpu, msr);
> +		break;
> +	default:
> +		ret = 1;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
>  static int synic_get_msr(struct kvm_vcpu_hv_synic *synic, u32 msr, u64 *pdata,
>  			 bool host)
>  {
> @@ -800,6 +860,8 @@ static bool kvm_hv_msr_partition_wide(u32 msr)
>  	case HV_X64_MSR_REENLIGHTENMENT_CONTROL:
>  	case HV_X64_MSR_TSC_EMULATION_CONTROL:
>  	case HV_X64_MSR_TSC_EMULATION_STATUS:
> +	case HV_X64_MSR_SYNDBG_OPTIONS:
> +	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
>  		r = true;
>  		break;
>  	}
> @@ -1061,6 +1123,11 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
>  		if (!host)
>  			return 1;
>  		break;
> +	case HV_X64_MSR_SYNDBG_OPTIONS:
> +		hv->hv_syndbg_options = data;
> +		break;
> +	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
> +		return syndbg_set_msr(vcpu, msr, data);
>  	default:
>  		vcpu_unimpl(vcpu, "Hyper-V unhandled wrmsr: 0x%x data 0x%llx\n",
>  			    msr, data);
> @@ -1227,6 +1294,24 @@ static int kvm_hv_get_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
>  	case HV_X64_MSR_TSC_EMULATION_STATUS:
>  		data = hv->hv_tsc_emulation_status;
>  		break;
> +	case HV_X64_MSR_SYNDBG_OPTIONS:
> +		data = hv->hv_syndbg_options;
> +		break;
> +	case HV_X64_MSR_SYNDBG_CONTROL:
> +		data = hv->hv_syndbg.control;
> +		break;
> +	case HV_X64_MSR_SYNDBG_STATUS:
> +		data = hv->hv_syndbg.status;
> +		break;
> +	case HV_X64_MSR_SYNDBG_SEND_BUFFER:
> +		data = hv->hv_syndbg.send_page;
> +		break;
> +	case HV_X64_MSR_SYNDBG_RECV_BUFFER:
> +		data = hv->hv_syndbg.recv_page;
> +		break;
> +	case HV_X64_MSR_SYNDBG_PENDING_BUFFER:
> +		data = hv->hv_syndbg.pending_page;
> +		break;
>  	default:
>  		vcpu_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);
>  		return 1;
> @@ -1797,6 +1882,9 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  		{ .function = HYPERV_CPUID_ENLIGHTMENT_INFO },
>  		{ .function = HYPERV_CPUID_IMPLEMENT_LIMITS },
>  		{ .function = HYPERV_CPUID_NESTED_FEATURES },
> +		{ .function = HYPERV_CPUID_SYNDBG_VENDOR_AND_MAX_FUNCTIONS },
> +		{ .function = HYPERV_CPUID_SYNDBG_INTERFACE },
> +		{ .function = HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES	},

HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS now returns
'HYPERV_CPUID_NESTED_FEATURES' as the last available leaf and I don't
see you adjusting it - is this expected?

>  	};
>  	int i, nent = ARRAY_SIZE(cpuid_entries);
>  
> @@ -1856,9 +1944,12 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  
>  			ent->ebx |= HV_X64_POST_MESSAGES;
>  			ent->ebx |= HV_X64_SIGNAL_EVENTS;
> +			ent->ebx |= HV_X64_DEBUGGING;
>  
>  			ent->edx |= HV_FEATURE_FREQUENCY_MSRS_AVAILABLE;
>  			ent->edx |= HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE;
> +			ent->edx |= HV_X64_GUEST_DEBUGGING_AVAILABLE;
> +			ent->edx |= HV_FEATURE_DEBUG_MSRS_AVAILABLE;
>  
>  			/*
>  			 * Direct Synthetic timers only make sense with in-kernel
> @@ -1903,6 +1994,24 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  
>  			break;
>  
> +		case HYPERV_CPUID_SYNDBG_VENDOR_AND_MAX_FUNCTIONS:
> +			memcpy(signature, "Microsoft VS", 12);

Does this string matter? E.g. for HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS
we call ourselves "Linux KVM Hv", I think we should do the same here.

> +
> +			ent->eax = 0;
> +			ent->ebx = signature[0];
> +			ent->ecx = signature[1];
> +			ent->edx = signature[2];
> +			break;
> +
> +		case HYPERV_CPUID_SYNDBG_INTERFACE:
> +			memcpy(signature, "VS#1\0\0\0\0\0\0\0\0", 12);
> +			ent->eax = signature[0];
> +			break;
> +
> +		case HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES:
> +			ent->eax |= HV_X64_SYNDBG_CAP_ALLOW_KERNEL_DEBUGGING;
> +			break;
> +
>  		default:
>  			break;
>  		}
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index 757cb578101c..6a86151fac53 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -46,6 +46,11 @@ static inline struct kvm_vcpu *synic_to_vcpu(struct kvm_vcpu_hv_synic *synic)
>  	return hv_vcpu_to_vcpu(container_of(synic, struct kvm_vcpu_hv, synic));
>  }
>  
> +static inline struct kvm_hv_syndbg *vcpu_to_hv_syndbg(struct kvm_vcpu *vcpu)
> +{
> +	return &vcpu->kvm->arch.hyperv.hv_syndbg;
> +}
> +
>  int kvm_hv_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host);
>  int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host);
>  
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index f194dd058470..235b9ab673a2 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -1515,6 +1515,28 @@ TRACE_EVENT(kvm_nested_vmenter_failed,
>  		__print_symbolic(__entry->err, VMX_VMENTER_INSTRUCTION_ERRORS))
>  );
>  
> +/*
> + * Tracepoint for syndbg_set_msr.
> + */
> +TRACE_EVENT(kvm_hv_syndbg_set_msr,
> +	TP_PROTO(int vcpu_id, u32 msr, u64 data),
> +	TP_ARGS(vcpu_id, msr, data),
> +
> +	TP_STRUCT__entry(
> +		__field(int, vcpu_id)
> +		__field(u32, msr)
> +		__field(u64, data)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->vcpu_id = vcpu_id;
> +		__entry->msr = msr;
> +		__entry->data = data;
> +	),
> +
> +	TP_printk("vcpu_id %d msr 0x%x data 0x%llx",
> +		  __entry->vcpu_id, __entry->msr, __entry->data)

This doesn't give us any additional data trace_kvm_msr_* points are more
or less the same. I think we can do better, e.g. for Hyper-V specific
things log the processor's VP index.

> +);
>  #endif /* _TRACE_KVM_H */
>  
>  #undef TRACE_INCLUDE_PATH
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5de200663f51..9d4d72a88572 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1214,6 +1214,10 @@ static const u32 emulated_msrs_all[] = {
>  	HV_X64_MSR_VP_ASSIST_PAGE,
>  	HV_X64_MSR_REENLIGHTENMENT_CONTROL, HV_X64_MSR_TSC_EMULATION_CONTROL,
>  	HV_X64_MSR_TSC_EMULATION_STATUS,
> +	HV_X64_MSR_SYNDBG_OPTIONS,
> +	HV_X64_MSR_SYNDBG_CONTROL, HV_X64_MSR_SYNDBG_STATUS,
> +	HV_X64_MSR_SYNDBG_SEND_BUFFER, HV_X64_MSR_SYNDBG_RECV_BUFFER,
> +	HV_X64_MSR_SYNDBG_PENDING_BUFFER,
>  
>  	MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
>  	MSR_KVM_PV_EOI_EN,
> @@ -2906,6 +2910,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		 */
>  		break;
>  	case HV_X64_MSR_GUEST_OS_ID ... HV_X64_MSR_SINT15:
> +	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
> +	case HV_X64_MSR_SYNDBG_OPTIONS:
>  	case HV_X64_MSR_CRASH_P0 ... HV_X64_MSR_CRASH_P4:
>  	case HV_X64_MSR_CRASH_CTL:
>  	case HV_X64_MSR_STIMER0_CONFIG ... HV_X64_MSR_STIMER3_COUNT:
> @@ -3151,6 +3157,8 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		msr_info->data = 0x20000000;
>  		break;
>  	case HV_X64_MSR_GUEST_OS_ID ... HV_X64_MSR_SINT15:
> +	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
> +	case HV_X64_MSR_SYNDBG_OPTIONS:
>  	case HV_X64_MSR_CRASH_P0 ... HV_X64_MSR_CRASH_P4:
>  	case HV_X64_MSR_CRASH_CTL:
>  	case HV_X64_MSR_STIMER0_CONFIG ... HV_X64_MSR_STIMER3_COUNT:
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4b95f9a31a2f..fae8cf608976 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -188,6 +188,7 @@ struct kvm_s390_cmma_log {
>  struct kvm_hyperv_exit {
>  #define KVM_EXIT_HYPERV_SYNIC          1
>  #define KVM_EXIT_HYPERV_HCALL          2
> +#define KVM_EXIT_HYPERV_SYNDBG         3
>  	__u32 type;
>  	union {
>  		struct {
> @@ -201,6 +202,14 @@ struct kvm_hyperv_exit {
>  			__u64 result;
>  			__u64 params[2];
>  		} hcall;
> +		struct {
> +			__u32 msr;
> +			__u64 control;
> +			__u64 status;
> +			__u64 send_page;
> +			__u64 recv_page;
> +			__u64 pending_page;
> +		} syndbg;
>  	} u;
>  };

Not your fault but I just noticed that 'struct kvm_hyperv_exit' is not
properly padded. 'synic' struct is OK, however, 'hcall' is not as
there's gonna be a gap between '__u32 type' and it. Your 'struct syndbg'
is also OK as it starts with '__u32 msr' but we should do something
about hcall.

-- 
Vitaly