[PATCH v1 0/3] x86/kvm/hyper-v: add support for synthetic debugger

[PATCH v1 0/3] x86/kvm/hyper-v: add support for synthetic debugger

[Jon Doron]

Add support for the synthetic debugger interface of hyper-v, the
synthetic debugger has 2 modes.
1. Use a set of MSRs to send/recv information
2. Use hypercalls

The first mode is based the following MSRs:
1. Control/Status MSRs which either asks for a send/recv .
2. Send/Recv MSRs each holds GPA where the send/recv buffers are.
3. Pending MSR, holds a GPA to a PAGE that simply has a boolean that
   indicates if there is data pending to issue a recv VMEXIT.

In the first patch the first mode is being implemented in the sense that
it simply exits to user-space when a control MSR is being written and
when the pending MSR is being set, then it's up-to userspace to
implement the rest of the logic of sending/recving.

In the second mode instead of using MSRs KNet will simply issue
Hypercalls with the information to send/recv, in this mode the data
being transferred is UDP encapsulated, unlike in the previous mode in
which you get just the data to send.

The new hypercalls will exit to userspace which will be incharge of
re-encapsulating if needed the UDP packets to be sent.

There is an issue though in which KDNet does not respect the hypercall
page and simply issues vmcall/vmmcall instructions depending on the cpu
type expecting them to be handled as it a real hypercall was issued.

Jon Doron (3):
  x86/kvm/hyper-v: Add support for synthetic debugger capability
  x86/kvm/hyper-v: enable hypercalls regardless of hypercall page
  x86/kvm/hyper-v: Add support for synthetic debugger via hypercalls

 arch/x86/include/asm/hyperv-tlfs.h |  21 +++++
 arch/x86/include/asm/kvm_host.h    |  11 +++
 arch/x86/kvm/hyperv.c              | 122 ++++++++++++++++++++++++++++-
 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, 197 insertions(+), 1 deletion(-)

-- 
2.24.1

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

[Jon Doron]

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.

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
 
 #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;
 };
 
 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);
+}
+
+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	},
 	};
 	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);
+
+			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)
+);
 #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;
 };
 
-- 
2.24.1

[PATCH v1 2/3] x86/kvm/hyper-v: enable hypercalls regardless of hypercall page

[Jon Doron]

Microsoft's kdvm.dll dbgtransport module does not respect the hypercall
page and simply identifies the CPU being used (AMD/Intel) and according
to it simply makes hypercalls with the relevant instruction
(vmmcall/vmcall respectively).

The relevant function in kdvm is KdHvConnectHypervisor which first checks
if the hypercall page has been enabled via HV_X64_MSR_HYPERCALL_ENABLE,
and in case it was not it simply sets the HV_X64_MSR_GUEST_OS_ID to
0x1000101010001 which means:
build_number = 0x0001
service_version = 0x01
minor_version = 0x01
major_version = 0x01
os_id = 0x00 (Undefined)
vendor_id = 1 (Microsoft)
os_type = 0 (A value of 0 indicates a proprietary, closed source OS)

and starts issuing the hypercall without setting the hypercall page.

To resolve this issue simply enable hypercalls if the guest_os_id is
not 0.

Signed-off-by: Jon Doron <arilou@gmail.com>
---
 arch/x86/kvm/hyperv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 13176ec23496..7ec962d433af 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1615,7 +1615,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *current_vcpu, u64 ingpa, u64 outgpa,
 
 bool kvm_hv_hypercall_enabled(struct kvm *kvm)
 {
-	return READ_ONCE(kvm->arch.hyperv.hv_hypercall) & HV_X64_MSR_HYPERCALL_ENABLE;
+	return READ_ONCE(kvm->arch.hyperv.hv_guest_os_id) != 0;
 }
 
 static void kvm_hv_hypercall_set_result(struct kvm_vcpu *vcpu, u64 result)
-- 
2.24.1

[PATCH v1 3/3] x86/kvm/hyper-v: Add support for synthetic debugger via hypercalls

[Jon Doron]

There is another mode for the synthetic debugger which uses hypercalls
to send/recv network data instead of the MSR interface.

This interface is much slower and less recommended since you might get
a lot of VMExits while KDVM polling for new packets to recv, rather
than simply checking the pending page to see if there is data avialble
and then request.

Signed-off-by: Jon Doron <arilou@gmail.com>
---
 arch/x86/include/asm/hyperv-tlfs.h |  5 +++++
 arch/x86/kvm/hyperv.c              | 11 +++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
index 8efdf974c23f..4fa6bf3732a6 100644
--- a/arch/x86/include/asm/hyperv-tlfs.h
+++ b/arch/x86/include/asm/hyperv-tlfs.h
@@ -283,6 +283,8 @@
 #define HV_X64_MSR_SYNDBG_PENDING_BUFFER	0x400000F5
 #define HV_X64_MSR_SYNDBG_OPTIONS		0x400000FF
 
+#define HV_X64_SYNDBG_OPTION_USE_HCALLS		BIT(2)
+
 /* Hyper-V guest crash notification MSR's */
 #define HV_X64_MSR_CRASH_P0			0x40000100
 #define HV_X64_MSR_CRASH_P1			0x40000101
@@ -392,6 +394,9 @@ struct hv_tsc_emulation_status {
 #define HVCALL_SEND_IPI_EX			0x0015
 #define HVCALL_POST_MESSAGE			0x005c
 #define HVCALL_SIGNAL_EVENT			0x005d
+#define HVCALL_POST_DEBUG_DATA			0x0069
+#define HVCALL_RETRIEVE_DEBUG_DATA		0x006a
+#define HVCALL_RESET_DEBUG_SESSION		0x006b
 #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE 0x00af
 #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_LIST 0x00b0
 
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 7ec962d433af..593e0f3f4dba 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1794,6 +1794,17 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 		}
 		ret = kvm_hv_send_ipi(vcpu, ingpa, outgpa, true, false);
 		break;
+	case HVCALL_POST_DEBUG_DATA:
+	case HVCALL_RETRIEVE_DEBUG_DATA:
+	case HVCALL_RESET_DEBUG_SESSION:
+		vcpu->run->exit_reason = KVM_EXIT_HYPERV;
+		vcpu->run->hyperv.type = KVM_EXIT_HYPERV_HCALL;
+		vcpu->run->hyperv.u.hcall.input = param;
+		vcpu->run->hyperv.u.hcall.params[0] = ingpa;
+		vcpu->run->hyperv.u.hcall.params[1] = outgpa;
+		vcpu->arch.complete_userspace_io =
+				kvm_hv_hypercall_complete_userspace;
+		return 0;
 	default:
 		ret = HV_STATUS_INVALID_HYPERCALL_CODE;
 		break;
-- 
2.24.1

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

[Vitaly Kuznetsov]

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

Re: [PATCH v1 2/3] x86/kvm/hyper-v: enable hypercalls regardless of hypercall page

[Vitaly Kuznetsov]

Jon Doron <arilou@gmail.com> writes:

> Microsoft's kdvm.dll dbgtransport module does not respect the hypercall
> page and simply identifies the CPU being used (AMD/Intel) and according
> to it simply makes hypercalls with the relevant instruction
> (vmmcall/vmcall respectively).
>
> The relevant function in kdvm is KdHvConnectHypervisor which first checks
> if the hypercall page has been enabled via HV_X64_MSR_HYPERCALL_ENABLE,
> and in case it was not it simply sets the HV_X64_MSR_GUEST_OS_ID to
> 0x1000101010001 which means:
> build_number = 0x0001
> service_version = 0x01
> minor_version = 0x01
> major_version = 0x01
> os_id = 0x00 (Undefined)
> vendor_id = 1 (Microsoft)
> os_type = 0 (A value of 0 indicates a proprietary, closed source OS)
>
> and starts issuing the hypercall without setting the hypercall page.
>
> To resolve this issue simply enable hypercalls if the guest_os_id is
> not 0.
>
> Signed-off-by: Jon Doron <arilou@gmail.com>
> ---
>  arch/x86/kvm/hyperv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 13176ec23496..7ec962d433af 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1615,7 +1615,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *current_vcpu, u64 ingpa, u64 outgpa,
>  
>  bool kvm_hv_hypercall_enabled(struct kvm *kvm)
>  {
> -	return READ_ONCE(kvm->arch.hyperv.hv_hypercall) & HV_X64_MSR_HYPERCALL_ENABLE;
> +	return READ_ONCE(kvm->arch.hyperv.hv_guest_os_id) != 0;
>  }
>  
>  static void kvm_hv_hypercall_set_result(struct kvm_vcpu *vcpu, u64 result)

I would've enabled it in both cases,

return (READ_ONCE(kvm->arch.hyperv.hv_hypercall) &
 HV_X64_MSR_HYPERCALL_ENABLE) || (READ_ONCE(kvm->arch.hyperv.hv_guest_os_id) != 0);

to be safe. We can also check what genuine Hyper-V does but I bet it has
hypercalls always enabled. Also, the function can be made inline,
there's a single caller.

-- 
Vitaly

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

[Jon Doron]

On Wed, Mar 4, 2020 at 3:51 PM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> 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.
>

Thanks will do in next version of this patchset.

> > 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...
>

Basically a lot of playing around with KDVM/KDNet by setting a kernel
debugger, there are
also few hints about how the transport for KD works in the DDK (there
are samples that
show how to code a new kdtransport)

> >
> >  #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()).
>

Done.

> >  };
> >
> >  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?)
>

Done.

> > +}
> > +
> > +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?
>

Good catch my bad :)

> >       };
> >       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.
>

Nope does not really matter since Userspace will override this anyway

> > +
> > +                     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.
>

Done.

> > +);
> >  #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.
>

Created another patch to address this.

> --
> Vitaly
>

Cheers,
-- Jon.

Re: [PATCH v1 2/3] x86/kvm/hyper-v: enable hypercalls regardless of hypercall page

[Jon Doron]

On Wed, Mar 4, 2020 at 3:58 PM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Jon Doron <arilou@gmail.com> writes:
>
> > Microsoft's kdvm.dll dbgtransport module does not respect the hypercall
> > page and simply identifies the CPU being used (AMD/Intel) and according
> > to it simply makes hypercalls with the relevant instruction
> > (vmmcall/vmcall respectively).
> >
> > The relevant function in kdvm is KdHvConnectHypervisor which first checks
> > if the hypercall page has been enabled via HV_X64_MSR_HYPERCALL_ENABLE,
> > and in case it was not it simply sets the HV_X64_MSR_GUEST_OS_ID to
> > 0x1000101010001 which means:
> > build_number = 0x0001
> > service_version = 0x01
> > minor_version = 0x01
> > major_version = 0x01
> > os_id = 0x00 (Undefined)
> > vendor_id = 1 (Microsoft)
> > os_type = 0 (A value of 0 indicates a proprietary, closed source OS)
> >
> > and starts issuing the hypercall without setting the hypercall page.
> >
> > To resolve this issue simply enable hypercalls if the guest_os_id is
> > not 0.
> >
> > Signed-off-by: Jon Doron <arilou@gmail.com>
> > ---
> >  arch/x86/kvm/hyperv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> > index 13176ec23496..7ec962d433af 100644
> > --- a/arch/x86/kvm/hyperv.c
> > +++ b/arch/x86/kvm/hyperv.c
> > @@ -1615,7 +1615,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *current_vcpu, u64 ingpa, u64 outgpa,
> >
> >  bool kvm_hv_hypercall_enabled(struct kvm *kvm)
> >  {
> > -     return READ_ONCE(kvm->arch.hyperv.hv_hypercall) & HV_X64_MSR_HYPERCALL_ENABLE;
> > +     return READ_ONCE(kvm->arch.hyperv.hv_guest_os_id) != 0;
> >  }
> >
> >  static void kvm_hv_hypercall_set_result(struct kvm_vcpu *vcpu, u64 result)
>
> I would've enabled it in both cases,
>
> return (READ_ONCE(kvm->arch.hyperv.hv_hypercall) &
>  HV_X64_MSR_HYPERCALL_ENABLE) || (READ_ONCE(kvm->arch.hyperv.hv_guest_os_id) != 0);
>
> to be safe. We can also check what genuine Hyper-V does but I bet it has
> hypercalls always enabled. Also, the function can be made inline,
> there's a single caller.

I dont have any Hyper-V setup at the moment to validate this, i
believe your hunch is correct but ill do the
implementation you have suggested.

>
> --
> Vitaly
>

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

[Jon Doron]

On Wed, Mar 4, 2020 at 4:00 PM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Jon Doron <arilou@gmail.com> writes:
>
> > There is another mode for the synthetic debugger which uses hypercalls
> > to send/recv network data instead of the MSR interface.
> >
> > This interface is much slower and less recommended since you might get
> > a lot of VMExits while KDVM polling for new packets to recv, rather
> > than simply checking the pending page to see if there is data avialble
> > and then request.
> >
> > Signed-off-by: Jon Doron <arilou@gmail.com>
> > ---
> >  arch/x86/include/asm/hyperv-tlfs.h |  5 +++++
> >  arch/x86/kvm/hyperv.c              | 11 +++++++++++
> >  2 files changed, 16 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> > index 8efdf974c23f..4fa6bf3732a6 100644
> > --- a/arch/x86/include/asm/hyperv-tlfs.h
> > +++ b/arch/x86/include/asm/hyperv-tlfs.h
> > @@ -283,6 +283,8 @@
> >  #define HV_X64_MSR_SYNDBG_PENDING_BUFFER     0x400000F5
> >  #define HV_X64_MSR_SYNDBG_OPTIONS            0x400000FF
> >
> > +#define HV_X64_SYNDBG_OPTION_USE_HCALLS              BIT(2)
> > +
>
> BIT(2) of what? :-) Also, you don't seem to use this define anywhere.
>

Will use it now :) and it's a syndbg MSR option bit

> >  /* Hyper-V guest crash notification MSR's */
> >  #define HV_X64_MSR_CRASH_P0                  0x40000100
> >  #define HV_X64_MSR_CRASH_P1                  0x40000101
> > @@ -392,6 +394,9 @@ struct hv_tsc_emulation_status {
> >  #define HVCALL_SEND_IPI_EX                   0x0015
> >  #define HVCALL_POST_MESSAGE                  0x005c
> >  #define HVCALL_SIGNAL_EVENT                  0x005d
> > +#define HVCALL_POST_DEBUG_DATA                       0x0069
> > +#define HVCALL_RETRIEVE_DEBUG_DATA           0x006a
> > +#define HVCALL_RESET_DEBUG_SESSION           0x006b
> >  #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE 0x00af
> >  #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_LIST 0x00b0
> >
> > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> > index 7ec962d433af..593e0f3f4dba 100644
> > --- a/arch/x86/kvm/hyperv.c
> > +++ b/arch/x86/kvm/hyperv.c
> > @@ -1794,6 +1794,17 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> >               }
> >               ret = kvm_hv_send_ipi(vcpu, ingpa, outgpa, true, false);
> >               break;
> > +     case HVCALL_POST_DEBUG_DATA:
> > +     case HVCALL_RETRIEVE_DEBUG_DATA:
> > +     case HVCALL_RESET_DEBUG_SESSION:
> > +             vcpu->run->exit_reason = KVM_EXIT_HYPERV;
> > +             vcpu->run->hyperv.type = KVM_EXIT_HYPERV_HCALL;
> > +             vcpu->run->hyperv.u.hcall.input = param;
> > +             vcpu->run->hyperv.u.hcall.params[0] = ingpa;
> > +             vcpu->run->hyperv.u.hcall.params[1] = outgpa;
> > +             vcpu->arch.complete_userspace_io =
> > +                             kvm_hv_hypercall_complete_userspace;
> > +             return 0;
> >       default:
> >               ret = HV_STATUS_INVALID_HYPERCALL_CODE;
> >               break;
>
> --
> Vitaly
>