Re: [PATCH v4 5/5] x86/hyperv: VTL support for Hyper-V

From: Stanislav Kinsburskii
Date: Fri Apr 07 2023 - 14:05:32 EST

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On Tue, Apr 04, 2023 at 02:01:04AM -0700, Saurabh Sengar wrote:
> 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 VTL0, 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.
>
> Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> ---
> [V4]
> - replace initial_stack with current->thread.sp as per recent upstream changes
>
> arch/x86/hyperv/Makefile | 1 +
> arch/x86/hyperv/hv_vtl.c | 227 ++++++++++++++++++++++++++++++++
> arch/x86/include/asm/mshyperv.h | 10 ++
> arch/x86/kernel/cpu/mshyperv.c | 1 +
> 4 files changed, 239 insertions(+)
> create mode 100644 arch/x86/hyperv/hv_vtl.c
>
> diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
> index 5d2de10809ae..3a1548054b48 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_MODE) += 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..1ba5d3b99b16
> --- /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@xxxxxxxxxxxxx>
> + */
> +
> +#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("Linux runs in Hyper-V Virtual Trust Level\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;

Nit: this code is VTL feature and hypevisor specific.
Defining vtl_get_rtc_noop instead of exporting get_rtc_noop would allow to make
this series less intrusive to the rest of x86 generic code.

Reviewed-by: Stanislav Kinsburskii <stanislav.kinsburskii@xxxxxxxxx>

> + 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 = current->thread.sp;
> + 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 = *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 = *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");
> +
> + 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/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 71ed240ef66d..de4ad38f7d74 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -19,6 +19,10 @@
> */
> #define HV_IOAPIC_BASE_ADDRESS 0xfec00000
>
> +#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);
> @@ -276,6 +280,12 @@ static inline u64 hv_get_non_nested_register(unsigned int reg) { return 0; }
> #endif /* CONFIG_HYPERV */
>
>
> +#ifdef CONFIG_HYPERV_VTL_MODE
> +void __init hv_vtl_init_platform(void);
> +#else
> +static inline void __init hv_vtl_init_platform(void) {}
> +#endif
> +
> #include <asm-generic/mshyperv.h>
>
> #endif
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 5ee02af57dac..5180e3c50184 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -519,6 +519,7 @@ 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
> --
> 2.34.1

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