hv_vtl.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2023, Microsoft Corporation.
 *
 * Author:
 *   Saurabh Sengar <[email protected]>
 */

#include <asm/apic.h>
#include <asm/boot.h>
#include <asm/desc.h>
#include <asm/i8259.h>
#include <asm/mshyperv.h>
#include <asm/msr.h>
#include <asm/realmode.h>
#include <asm/reboot.h>
#include <../kernel/smpboot.h>

extern struct boot_params boot_params;
static struct real_mode_header hv_vtl_real_mode_header;

static bool __init hv_vtl_msi_ext_dest_id(void)
{
	return true;
}

/*
 * The `native_machine_emergency_restart` function from `reboot.c` writes
 * to the physical address 0x472 to indicate the type of reboot for the
 * firmware. We cannot have that in VSM as the memory composition might
 * be more generic, and such write effectively corrupts the memory thus
 * making diagnostics harder at the very least.
 */
static void  __noreturn hv_vtl_emergency_restart(void)
{
	/*
	 * Cause a triple fault and the immediate reset. Here the code does not run
	 * on the top of any firmware, whereby cannot reach out to its services.
	 * The inifinite loop is for the improbable case that the triple fault does
	 * not work and have to preserve the state intact for debugging.
	 */
	for (;;) {
		idt_invalidate();
		__asm__ __volatile__("int3");
	}
}

/*
 * The only way to restart in the VTL mode is to triple fault as the kernel runs
 * as firmware.
 */
static void  __noreturn hv_vtl_restart(char __maybe_unused *cmd)
{
	hv_vtl_emergency_restart();
}

void __init hv_vtl_init_platform(void)
{
	/*
	 * This function is a no-op if the VTL mode is not enabled.
	 * If it is, this function runs if and only the kernel boots in
	 * VTL2 which the x86 hv initialization path makes sure of.
	 */
	pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);

	x86_platform.realmode_reserve = x86_init_noop;
	x86_platform.realmode_init = x86_init_noop;
	x86_init.irqs.pre_vector_init = x86_init_noop;
	x86_init.timers.timer_init = x86_init_noop;
	x86_init.resources.probe_roms = x86_init_noop;

	/* Avoid searching for BIOS MP tables */
	x86_init.mpparse.find_mptable = x86_init_noop;
	x86_init.mpparse.early_parse_smp_cfg = 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;

	x86_init.hyper.msi_ext_dest_id = hv_vtl_msi_ext_dest_id;
}

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, int cpu, 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;

	struct task_struct *idle = idle_thread_get(cpu);
	u64 rsp = (unsigned long)idle->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 = native_rdmsrq(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 = native_rdmsrq(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_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip, unsigned int cpu)
{
	int vp_index;

	pr_debug("Bringing up CPU with APIC ID %d in VTL2...\n", apicid);
	vp_index = hv_apicid_to_vp_index(apicid);

	if (vp_index < 0) {
		pr_err("Couldn't find CPU with APIC ID %d\n", apicid);
		return -EINVAL;
	}
	if (vp_index > ms_hyperv.max_vp_index) {
		pr_err("Invalid CPU id %d for APIC ID %d\n", vp_index, apicid);
		return -EINVAL;
	}

	return hv_vtl_bringup_vcpu(vp_index, cpu, start_eip);
}

int __init hv_vtl_early_init(void)
{
	machine_ops.emergency_restart = hv_vtl_emergency_restart;
	machine_ops.restart = hv_vtl_restart;

	/*
	 * `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_update_callback(wakeup_secondary_cpu_64, hv_vtl_wakeup_secondary_cpu);

	return 0;
}