Date:   Thu, 2 Mar 2023 21:54:16 -0800
From:   Saurabh Singh Sengar <ssengar@linux.microsoft.com>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>
Cc:     "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "arnd@arndb.de" <arnd@arndb.de>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 2/2] x86/hyperv: VTL support for Hyper-V
Message-ID: <20230303055416.GA22929@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
References: <1677665288-6879-1-git-send-email-ssengar@linux.microsoft.com>
 <1677665288-6879-3-git-send-email-ssengar@linux.microsoft.com>
 <BYAPR21MB16889D8038E051CB4AEC3B9AD7B29@BYAPR21MB1688.namprd21.prod.outlook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <BYAPR21MB16889D8038E051CB4AEC3B9AD7B29@BYAPR21MB1688.namprd21.prod.outlook.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Precedence: bulk

Thanks for your review and suggestions. I will incorporate them in V2.

- Saurabh


On Thu, Mar 02, 2023 at 08:14:51PM +0000, Michael Kelley (LINUX) wrote:
> From: Saurabh Sengar <ssengar@linux.microsoft.com> Sent: Wednesday, March 1, 2023 2:08 AM
> > 
> > VTL helps enable Hyper-V Virtual Secure Mode (VSM) feature. VSM is a
> 
> I'd suggest putting the full expansion "Virtual Trust Levels (VTL)" here
> at first use, rather than at the beginning of the second paragraph.
> 
> > set of hypervisor capabilities and enlightenments offered to host and
> > guest partitions which enable the creation and management of new
> > security boundaries within operating system software. VSM achieves
> > and maintains isolation through VTLs.
> > 
> > Add early initialization for Virtual Trust Levels (VTL). This includes
> > initializing the x86 platform for VTL and enabling boot support for
> > secondary CPUs to start in targeted VTL context. For now, only enable
> > the code for targeted VTL level as 2.
> > 
> > In VTL, AP has to start directly in the 64-bit mode, bypassing the
> 
> Suggested revised wording:
> 
> When starting an AP at a VTL other than VTL 0, the AP must start directly
> in 64-bit mode, bypassing the 
> 
> > usual 16-bit -> 32-bit -> 64-bit mode transition sequence that occurs
> > after waking up an AP with SIPI whose vector points to the 16-bit AP
> > startup trampoline code.
> > 
> > This commit also moves hv_get_nmi_reason function to header file, so
> > that it can be reused by VTL.
> > 
> > Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > ---
> >  arch/x86/Kconfig                   |  23 +++
> >  arch/x86/hyperv/Makefile           |   1 +
> >  arch/x86/hyperv/hv_vtl.c           | 242 +++++++++++++++++++++++++++++
> >  arch/x86/include/asm/hyperv-tlfs.h |  75 +++++++++
> >  arch/x86/include/asm/mshyperv.h    |  14 ++
> >  arch/x86/kernel/cpu/mshyperv.c     |   6 +-
> >  include/asm-generic/hyperv-tlfs.h  |   4 +
> >  7 files changed, 360 insertions(+), 5 deletions(-)
> >  create mode 100644 arch/x86/hyperv/hv_vtl.c
> > 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 947e24714c28..e0d074bd04ce 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -781,6 +781,29 @@ menuconfig HYPERVISOR_GUEST
> > 
> >  if HYPERVISOR_GUEST
> > 
> > +config HYPERV_VTL
> > +	bool "Enable VTL"
> > +	depends on X86_64 && HYPERV
> > +	default n
> > +	help
> > +	  Virtual Secure Mode (VSM) is a set of hypervisor capabilities and
> > +	  enlightenments offered to host and guest partitions which enables
> > +	  the creation and management of new security boundaries within
> > +	  operating system software.
> > +
> > +	  VSM achieves and maintains isolation through Virtual Trust Levels
> > +	  (VTLs). Virtual Trust Levels are hierarchical, with higher levels
> > +	  being more privileged than lower levels. VTL0 is the least privileged
> > +	  level, and currently only other level supported is VTL2.
> > +
> > +	  Select this option to enable Hyper-V VTL configuration at boot
> > +	  time. This option initializes the x86 platform for VTL and add
> > +	  support to boot secondary CPUs directly in to 64 bit context as
> > +	  required by VTL.
> > +
> > +	  This option should only be enabled for the higher VTLs that is > 0.
> > +	  If unsure, say N.
> 
> The wording of the previous two paragraphs should be more explicit.  I'd
> suggest something like:
> 
> 	Select this option to build a Linux kernel to run at a VTL other than
> 	the normal VTL 0, which currently is only VTL 2.  This option initializes
> 	the x86 platform for VTL 2, and adds the ability to boot secondary CPUs
> 	directly into 64-bit context as required for VTLs other than 0.  A kernel
> 	built with this option must run at VTL 2, and will not run as a normal
> 	guest.
> 
> 	If unsure, say N.
> 
> > +
> >  config PARAVIRT
> >  	bool "Enable paravirtualization code"
> >  	depends on HAVE_STATIC_CALL
> > diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
> > index 5d2de10809ae..a538df01181a 100644
> > --- a/arch/x86/hyperv/Makefile
> > +++ b/arch/x86/hyperv/Makefile
> > @@ -1,6 +1,7 @@
> >  # SPDX-License-Identifier: GPL-2.0-only
> >  obj-y			:= hv_init.o mmu.o nested.o irqdomain.o ivm.o
> >  obj-$(CONFIG_X86_64)	+= hv_apic.o hv_proc.o
> > +obj-$(CONFIG_HYPERV_VTL)	+= hv_vtl.o
> > 
> >  ifdef CONFIG_X86_64
> >  obj-$(CONFIG_PARAVIRT_SPINLOCKS)	+= hv_spinlock.o
> > diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> > new file mode 100644
> > index 000000000000..0b67e1bf017d
> > --- /dev/null
> > +++ b/arch/x86/hyperv/hv_vtl.c
> > @@ -0,0 +1,242 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2023, Microsoft Corporation.
> > + *
> > + * Author:
> > + *   Saurabh Sengar <ssengar@microsoft.com>
> > + */
> > +
> > +#include <asm/apic.h>
> > +#include <asm/boot.h>
> > +#include <asm/desc.h>
> > +#include <asm/i8259.h>
> > +#include <asm/mshyperv.h>
> > +#include <asm/realmode.h>
> > +
> > +extern struct boot_params boot_params;
> > +static struct real_mode_header hv_vtl_real_mode_header;
> > +
> > +static struct legacy_pic vtl_pic;
> > +
> > +static int vtl_pic_probe(void)
> > +{
> > +	null_legacy_pic.probe();
> > +	return vtl_pic.nr_legacy_irqs;
> > +}
> > +
> > +void __init hv_vtl_init_platform(void)
> > +{
> > +	pr_info("Initializing Hyper-V VTL\n");
> > +
> > +	x86_init.irqs.pre_vector_init = x86_init_noop;
> > +	x86_init.timers.timer_init = x86_init_noop;
> > +
> > +	x86_platform.get_wallclock = get_rtc_noop;
> > +	x86_platform.set_wallclock = set_rtc_noop;
> > +	x86_platform.get_nmi_reason = hv_get_nmi_reason;
> > +
> > +	x86_platform.legacy.i8042 = X86_LEGACY_I8042_PLATFORM_ABSENT;
> > +	x86_platform.legacy.rtc = 0;
> > +	x86_platform.legacy.warm_reset = 0;
> > +	x86_platform.legacy.reserve_bios_regions = 0;
> > +	x86_platform.legacy.devices.pnpbios = 0;
> > +	/*
> > +	 * Do not try to access the PIC (even if it is there).
> > +	 * Reserve 1 IRQ so that PCI MSIs to not get allocated to virq 0,
> > +	 * which is not generally considered a valid IRQ by Linux (and so
> > +	 * causes various problems).
> > +	 */
> > +	vtl_pic = null_legacy_pic;
> > +	vtl_pic.nr_legacy_irqs = 1;
> > +	vtl_pic.probe = vtl_pic_probe;
> > +	legacy_pic = &vtl_pic;
> > +}
> > +
> > +static inline u64 hv_vtl_system_desc_base(struct ldttss_desc *desc)
> > +{
> > +	return ((u64)desc->base3 << 32) | ((u64)desc->base2 << 24) |
> > +		(desc->base1 << 16) | desc->base0;
> > +}
> > +
> > +static inline u32 hv_vtl_system_desc_limit(struct ldttss_desc *desc)
> > +{
> > +	return ((u32)desc->limit1 << 16) | (u32)desc->limit0;
> > +}
> > +
> > +typedef void (*secondary_startup_64_fn)(void*, void*);
> > +static void hv_vtl_ap_entry(void)
> > +{
> > +	((secondary_startup_64_fn)secondary_startup_64)(&boot_params, &boot_params);
> > +}
> > +
> > +static int hv_vtl_bringup_vcpu(u32 target_vp_index, u64 eip_ignored)
> > +{
> > +	u64 status;
> > +	struct hv_enable_vp_vtl *input;
> > +	unsigned long irq_flags;
> > +
> > +	struct desc_ptr gdt_ptr;
> > +	struct desc_ptr idt_ptr;
> > +
> > +	struct ldttss_desc *tss;
> > +	struct ldttss_desc *ldt;
> > +	struct desc_struct *gdt;
> > +
> > +	u64 rsp = initial_stack;
> > +	u64 rip = (u64)&hv_vtl_ap_entry;
> > +
> > +	native_store_gdt(&gdt_ptr);
> > +	store_idt(&idt_ptr);
> > +
> > +	gdt = (struct desc_struct *)((void *)(gdt_ptr.address));
> > +	tss = (struct ldttss_desc *)(gdt + GDT_ENTRY_TSS);
> > +	ldt = (struct ldttss_desc *)(gdt + GDT_ENTRY_LDT);
> > +
> > +	local_irq_save(irq_flags);
> > +
> > +	input = (struct hv_enable_vp_vtl *)(*this_cpu_ptr(hyperv_pcpu_input_arg));
> > +	memset(input, 0, sizeof(*input));
> > +
> > +	input->partition_id = HV_PARTITION_ID_SELF;
> > +	input->vp_index = target_vp_index;
> > +	input->target_vtl.target_vtl = HV_VTL_MGMT;
> > +
> > +	/*
> > +	 * The x86_64 Linux kernel follows the 16-bit -> 32-bit -> 64-bit
> > +	 * mode transition sequence after waking up an AP with SIPI whose
> > +	 * vector points to the 16-bit AP startup trampoline code. Here in
> > +	 * VTL2, we can't perform that sequence as the AP has to start in
> > +	 * the 64-bit mode.
> > +	 *
> > +	 * To make this happen, we tell the hypervisor to load a valid 64-bit
> > +	 * context (most of which is just magic numbers from the CPU manual)
> > +	 * so that AP jumps right to the 64-bit entry of the kernel, and the
> > +	 * control registers are loaded with values that let the AP fetch the
> > +	 * code and data and carry on with work it gets assigned.
> > +	 */
> > +
> > +	input->vp_context.rip = rip;
> > +	input->vp_context.rsp = rsp;
> > +	input->vp_context.rflags = 0x0000000000000002;
> > +	input->vp_context.efer = __rdmsr(MSR_EFER);
> > +	input->vp_context.cr0 = native_read_cr0();
> > +	input->vp_context.cr3 = __native_read_cr3();
> > +	input->vp_context.cr4 = native_read_cr4();
> > +	input->vp_context.msr_cr_pat = __rdmsr(MSR_IA32_CR_PAT);
> > +	input->vp_context.idtr.limit = idt_ptr.size;
> > +	input->vp_context.idtr.base = idt_ptr.address;
> > +	input->vp_context.gdtr.limit = gdt_ptr.size;
> > +	input->vp_context.gdtr.base = gdt_ptr.address;
> > +
> > +	/* Non-system desc (64bit), long, code, present */
> > +	input->vp_context.cs.selector = __KERNEL_CS;
> > +	input->vp_context.cs.base = 0;
> > +	input->vp_context.cs.limit = 0xffffffff;
> > +	input->vp_context.cs.attributes = 0xa09b;
> > +	/* Non-system desc (64bit), data, present, granularity, default */
> > +	input->vp_context.ss.selector = __KERNEL_DS;
> > +	input->vp_context.ss.base = 0;
> > +	input->vp_context.ss.limit = 0xffffffff;
> > +	input->vp_context.ss.attributes = 0xc093;
> > +
> > +	/* System desc (128bit), present, LDT */
> > +	input->vp_context.ldtr.selector = GDT_ENTRY_LDT * 8;
> > +	input->vp_context.ldtr.base = hv_vtl_system_desc_base(ldt);
> > +	input->vp_context.ldtr.limit = hv_vtl_system_desc_limit(ldt);
> > +	input->vp_context.ldtr.attributes = 0x82;
> > +
> > +	/* System desc (128bit), present, TSS, 0x8b - busy, 0x89 -- default */
> > +	input->vp_context.tr.selector = GDT_ENTRY_TSS * 8;
> > +	input->vp_context.tr.base = hv_vtl_system_desc_base(tss);
> > +	input->vp_context.tr.limit = hv_vtl_system_desc_limit(tss);
> > +	input->vp_context.tr.attributes = 0x8b;
> > +
> > +	status = hv_result(hv_do_hypercall(HVCALL_ENABLE_VP_VTL, input, NULL));
> 
> The normal pattern is to *not* use hv_result as a wrapper around hv_do_hypercall().
> Let the hypercall return the raw 64-bit status.  Then hv_result_success() and
> hv_result() take that raw 64-bit status as an input.
> 
> > +
> > +	if (!hv_result_success(status) && status != HV_STATUS_VTL_ALREADY_ENABLED) {
> 
> For the second check above, use hv_result(status) != HV_STATUS_VTL_ALREADY_ENABLED.
> The first check is correct if you remove the hv_result() around hv_do_hypercall().
> 
> > +		pr_err("HVCALL_ENABLE_VP_VTL failed for VP : %d ! [Err: %#llx\n]",
> > +		       target_vp_index, status);
> > +		status = -EINVAL;
> > +		goto free_lock;
> > +	}
> > +
> > +	status = hv_result(hv_do_hypercall(HVCALL_START_VP, input, NULL));
> 
> Again, the hv_result() above is unnecessary.  hv_result_success() below expects the
> raw 64-bit hypercall status as input.
> 
> > +
> > +	if (!hv_result_success(status)) {
> > +		pr_err("HVCALL_START_VP failed for VP : %d ! [Err: %#llx]\n",
> > +		       target_vp_index, status);
> > +		status = -EINVAL;
> > +	}
> > +
> > +free_lock:
> > +	local_irq_restore(irq_flags);
> > +
> > +	return status;
> > +}
> > +
> > +static int hv_vtl_apicid_to_vp_id(u32 apic_id)
> > +{
> > +	u64 control;
> > +	u64 status;
> > +	unsigned long irq_flags;
> > +	struct hv_get_vp_from_apic_id_in *input;
> > +	u32 *output;
> > +
> > +	local_irq_save(irq_flags);
> > +
> > +	input = (struct hv_get_vp_from_apic_id_in *)(*this_cpu_ptr(hyperv_pcpu_input_arg));
> > +	memset(input, 0, sizeof(*input));
> > +	input->partition_id = HV_PARTITION_ID_SELF;
> > +	input->apic_ids[0] = apic_id;
> > +
> > +	output = (u32 *)input;
> > +
> > +	control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_ID_FROM_APIC_ID;
> > +	status = hv_result(hv_do_hypercall(control, input, output));
> 
> Same: don't use hv_result() here.
> 
> > +
> > +	local_irq_restore(irq_flags);
> > +
> > +	if (!hv_result_success(status)) {
> > +		pr_err("failed to get vp id from apic id %d, status %#llx\n",
> > +		       apic_id, status);
> > +		return -EINVAL;
> > +	}
> > +
> > +	return output[0];
> 
> The value of output[0] must be copied to a local variable *before* the
> call to local_irq_restore().  Once local_irq_restore() is called, you must not
> access the hyperv_pcpu_input_arg any longer, since preemption could occur
> and the hyperv_pcpu_input_arg could get reused.
> 
> > +}
> > +
> > +static int hv_vtl_wakeup_secondary_cpu(int apicid, unsigned long start_eip)
> > +{
> > +	int vp_id;
> > +
> > +	pr_debug("Bringing up CPU with APIC ID %d in VTL2...\n", apicid);
> > +	vp_id = hv_vtl_apicid_to_vp_id(apicid);
> > +
> > +	if (vp_id < 0) {
> > +		pr_err("Couldn't find CPU with APIC ID %d\n", apicid);
> > +		return -EINVAL;
> > +	}
> > +	if (vp_id > ms_hyperv.max_vp_index) {
> > +		pr_err("Invalid CPU id %d for APIC ID %d\n", vp_id, apicid);
> > +		return -EINVAL;
> > +	}
> > +
> > +	return hv_vtl_bringup_vcpu(vp_id, start_eip);
> > +}
> > +
> > +static int __init hv_vtl_early_init(void)
> > +{
> > +	/*
> > +	 * `boot_cpu_has` returns the runtime feature support,
> > +	 * and here is the earliest it can be used.
> > +	 */
> > +	if (boot_cpu_has(X86_FEATURE_XSAVE))
> > +		panic("XSAVE has to be disabled as it is not supported by this module.\n"
> > +			  "Please add 'noxsave' to the kernel command line.\n");
> > +
> > +	real_mode_header = &hv_vtl_real_mode_header;
> > +	apic->wakeup_secondary_cpu_64 = hv_vtl_wakeup_secondary_cpu;
> > +
> > +	return 0;
> > +}
> > +early_initcall(hv_vtl_early_init);
> > diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> > index 0b73a809e9e1..08a6845a233d 100644
> > --- a/arch/x86/include/asm/hyperv-tlfs.h
> > +++ b/arch/x86/include/asm/hyperv-tlfs.h
> > @@ -713,6 +713,81 @@ union hv_msi_entry {
> >  	} __packed;
> >  };
> > 
> > +struct hv_x64_segment_register {
> > +	__u64 base;
> > +	__u32 limit;
> > +	__u16 selector;
> > +	union {
> > +		struct {
> > +			__u16 segment_type : 4;
> > +			__u16 non_system_segment : 1;
> > +			__u16 descriptor_privilege_level : 2;
> > +			__u16 present : 1;
> > +			__u16 reserved : 4;
> > +			__u16 available : 1;
> > +			__u16 _long : 1;
> > +			__u16 _default : 1;
> > +			__u16 granularity : 1;
> > +		} __packed;
> > +		__u16 attributes;
> > +	};
> > +} __packed;
> > +
> > +struct hv_x64_table_register {
> > +	__u16 pad[3];
> > +	__u16 limit;
> > +	__u64 base;
> > +} __packed;
> > +
> > +struct hv_init_vp_context_t {
> > +	u64 rip;
> > +	u64 rsp;
> > +	u64 rflags;
> > +
> > +	struct hv_x64_segment_register cs;
> > +	struct hv_x64_segment_register ds;
> > +	struct hv_x64_segment_register es;
> > +	struct hv_x64_segment_register fs;
> > +	struct hv_x64_segment_register gs;
> > +	struct hv_x64_segment_register ss;
> > +	struct hv_x64_segment_register tr;
> > +	struct hv_x64_segment_register ldtr;
> > +
> > +	struct hv_x64_table_register idtr;
> > +	struct hv_x64_table_register gdtr;
> > +
> > +	u64 efer;
> > +	u64 cr0;
> > +	u64 cr3;
> > +	u64 cr4;
> > +	u64 msr_cr_pat;
> > +} __packed;
> > +
> > +union hv_input_vtl {
> > +	u8 as_uint8;
> > +	struct {
> > +		u8 target_vtl: 4;
> > +		u8 use_target_vtl: 1;
> > +		u8 reserved_z: 3;
> > +	};
> > +} __packed;
> > +
> > +struct hv_enable_vp_vtl {
> > +	u64				partition_id;
> > +	u32				vp_index;
> > +	union hv_input_vtl		target_vtl;
> > +	u8				mbz0;
> > +	u16				mbz1;
> > +	struct hv_init_vp_context_t	vp_context;
> > +} __packed;
> > +
> > +struct hv_get_vp_from_apic_id_in {
> > +	u64 partition_id;
> > +	union hv_input_vtl target_vtl;
> > +	u8 res[7];
> > +	u32 apic_ids[];
> > +} __packed;
> > +
> >  #include <asm-generic/hyperv-tlfs.h>
> > 
> >  #endif
> > diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> > index 4c4c0ec3b62e..4ff549dcd49a 100644
> > --- a/arch/x86/include/asm/mshyperv.h
> > +++ b/arch/x86/include/asm/mshyperv.h
> > @@ -11,6 +11,10 @@
> >  #include <asm/paravirt.h>
> >  #include <asm/mshyperv.h>
> > 
> > +#define HV_VTL_NORMAL 0x0
> > +#define HV_VTL_SECURE 0x1
> > +#define HV_VTL_MGMT   0x2
> > +
> >  union hv_ghcb;
> > 
> >  DECLARE_STATIC_KEY_FALSE(isolation_type_snp);
> > @@ -181,6 +185,11 @@ static inline struct hv_vp_assist_page
> > *hv_get_vp_assist_page(unsigned int cpu)
> >  	return hv_vp_assist_page[cpu];
> >  }
> > 
> > +static inline unsigned char hv_get_nmi_reason(void)
> > +{
> > +	return 0;
> > +}
> > +
> >  void __init hyperv_init(void);
> >  void hyperv_setup_mmu_ops(void);
> >  void set_hv_tscchange_cb(void (*cb)(void));
> > @@ -266,6 +275,11 @@ static inline int hv_set_mem_host_visibility(unsigned long
> > addr, int numpages,
> >  }
> >  #endif /* CONFIG_HYPERV */
> > 
> > +#ifdef CONFIG_HYPERV_VTL
> > +void __init hv_vtl_init_platform(void);
> > +#else
> > +static inline void __init hv_vtl_init_platform(void) {}
> > +#endif
> > 
> >  #include <asm-generic/mshyperv.h>
> > 
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> > index f36dc2f796c5..da5d13d29c4e 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -250,11 +250,6 @@ static uint32_t  __init ms_hyperv_platform(void)
> >  	return HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
> >  }
> > 
> > -static unsigned char hv_get_nmi_reason(void)
> > -{
> > -	return 0;
> > -}
> > -
> >  #ifdef CONFIG_X86_LOCAL_APIC
> >  /*
> >   * Prior to WS2016 Debug-VM sends NMIs to all CPUs which makes
> > @@ -521,6 +516,7 @@ static void __init ms_hyperv_init_platform(void)
> > 
> >  	/* Register Hyper-V specific clocksource */
> >  	hv_init_clocksource();
> > +	hv_vtl_init_platform();
> >  #endif
> >  	/*
> >  	 * TSC should be marked as unstable only after Hyper-V
> > diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> > index b870983596b9..87258341fd7c 100644
> > --- a/include/asm-generic/hyperv-tlfs.h
> > +++ b/include/asm-generic/hyperv-tlfs.h
> > @@ -146,6 +146,7 @@ union hv_reference_tsc_msr {
> >  /* Declare the various hypercall operations. */
> >  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE	0x0002
> >  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST	0x0003
> > +#define HVCALL_ENABLE_VP_VTL			0x000f
> >  #define HVCALL_NOTIFY_LONG_SPIN_WAIT		0x0008
> >  #define HVCALL_SEND_IPI				0x000b
> >  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX	0x0013
> > @@ -165,6 +166,8 @@ union hv_reference_tsc_msr {
> >  #define HVCALL_MAP_DEVICE_INTERRUPT		0x007c
> >  #define HVCALL_UNMAP_DEVICE_INTERRUPT		0x007d
> >  #define HVCALL_RETARGET_INTERRUPT		0x007e
> > +#define HVCALL_START_VP				0x0099
> > +#define HVCALL_GET_VP_ID_FROM_APIC_ID		0x009a
> >  #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE 0x00af
> >  #define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_LIST 0x00b0
> >  #define HVCALL_MODIFY_SPARSE_GPA_PAGE_HOST_VISIBILITY 0x00db
> > @@ -218,6 +221,7 @@ enum HV_GENERIC_SET_FORMAT {
> >  #define HV_STATUS_INVALID_PORT_ID		17
> >  #define HV_STATUS_INVALID_CONNECTION_ID		18
> >  #define HV_STATUS_INSUFFICIENT_BUFFERS		19
> > +#define HV_STATUS_VTL_ALREADY_ENABLED		134
> > 
> >  /*
> >   * The Hyper-V TimeRefCount register and the TSC
> > --
> > 2.34.1