Message-ID: <87a60gww0h.fsf@redhat.com>
Date:   Mon, 13 Mar 2023 15:45:02 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Saurabh Sengar <ssengar@...ux.microsoft.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, arnd@...db.de, tiala@...rosoft.com,
        mikelley@...rosoft.com, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 2/2] x86/hyperv: VTL support for Hyper-V

Saurabh Sengar <ssengar@...ux.microsoft.com> writes:

> Virtual Trust Levels (VTL) helps enable Hyper-V Virtual Secure Mode (VSM)
> feature. VSM is a 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.
>
> 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@...ux.microsoft.com>
> ---
>  arch/x86/Kconfig                   |  24 +++
>  arch/x86/hyperv/Makefile           |   1 +
>  arch/x86/hyperv/hv_vtl.c           | 227 +++++++++++++++++++++++++++++
>  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 +

This patch is quite big, I'd suggest you split it up. E.g. TLFS definitions
can easily be a separate patch. Moving hv_get_nmi_reason() can be a
separate patch. Secondary CPU bringup can be a separate patch. The new
config option to enable the feature (assuming it is really needed) can
be the last separate patch.

>  7 files changed, 346 insertions(+), 5 deletions(-)
>  create mode 100644 arch/x86/hyperv/hv_vtl.c
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 453f462f6c9c..b9e52ac9c9f9 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -782,6 +782,30 @@ 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 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.

This is quite unfortunate, is there a way to detect which VTL the guest
is running at and change the behavior dynamically?

> +
> +	  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..0da8b242eb8b
> --- /dev/null
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -0,0 +1,227 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2023, Microsoft Corporation.
> + *
> + * Author:
> + *   Saurabh Sengar <ssengar@...rosoft.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;
> +
> +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;
> +}
> +
> +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;
> +	int ret = 0;
> +	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_do_hypercall(HVCALL_ENABLE_VP_VTL, input, NULL);
> +
> +	if (!hv_result_success(status) &&
> +	    hv_result(status) != HV_STATUS_VTL_ALREADY_ENABLED) {
> +		pr_err("HVCALL_ENABLE_VP_VTL failed for VP : %d ! [Err: %#llx\n]",
> +		       target_vp_index, status);
> +		ret = -EINVAL;
> +		goto free_lock;
> +	}
> +
> +	status = hv_do_hypercall(HVCALL_START_VP, input, NULL);
> +
> +	if (!hv_result_success(status)) {
> +		pr_err("HVCALL_START_VP failed for VP : %d ! [Err: %#llx]\n",
> +		       target_vp_index, status);
> +		ret = -EINVAL;
> +	}
> +
> +free_lock:
> +	local_irq_restore(irq_flags);
> +
> +	return ret;
> +}
> +
> +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, ret;
> +
> +	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_do_hypercall(control, input, output);
> +	ret = output[0];
> +
> +	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 ret;
> +}
> +
> +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 (cpu_feature_enabled(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");

Can't we just suppress the feature early instead?

> +
> +	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

Don't these belong to hyperv-tlfs.h too (even if they're not directly
described in Hyper-V TLFS)?

> +
>  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

-- 
Vitaly

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