hv_vtl.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (c) 2023, Microsoft Corporation.
  4 *
  5 * Author:
  6 *   Saurabh Sengar <ssengar@microsoft.com>
  7 */
  8
  9#include <asm/apic.h>
 10#include <asm/boot.h>
 11#include <asm/desc.h>
 12#include <asm/fpu/api.h>
 13#include <asm/fpu/types.h>
 14#include <asm/i8259.h>
 15#include <asm/mshyperv.h>
 16#include <asm/msr.h>
 17#include <asm/realmode.h>
 18#include <asm/reboot.h>
 19#include <asm/smap.h>
 20#include <linux/export.h>
 21#include <../kernel/smpboot.h>
 22#include "../../kernel/fpu/legacy.h"
 23
 24extern struct boot_params boot_params;
 25static struct real_mode_header hv_vtl_real_mode_header;
 26
 27static bool __init hv_vtl_msi_ext_dest_id(void)
 28{
 29	return true;
 30}
 31
 32/*
 33 * The `native_machine_emergency_restart` function from `reboot.c` writes
 34 * to the physical address 0x472 to indicate the type of reboot for the
 35 * firmware. We cannot have that in VSM as the memory composition might
 36 * be more generic, and such write effectively corrupts the memory thus
 37 * making diagnostics harder at the very least.
 38 */
 39static void  __noreturn hv_vtl_emergency_restart(void)
 40{
 41	/*
 42	 * Cause a triple fault and the immediate reset. Here the code does not run
 43	 * on the top of any firmware, whereby cannot reach out to its services.
 44	 * The inifinite loop is for the improbable case that the triple fault does
 45	 * not work and have to preserve the state intact for debugging.
 46	 */
 47	for (;;) {
 48		idt_invalidate();
 49		__asm__ __volatile__("int3");
 50	}
 51}
 52
 53/*
 54 * The only way to restart in the VTL mode is to triple fault as the kernel runs
 55 * as firmware.
 56 */
 57static void  __noreturn hv_vtl_restart(char __maybe_unused *cmd)
 58{
 59	hv_vtl_emergency_restart();
 60}
 61
 62void __init hv_vtl_init_platform(void)
 63{
 64	/*
 65	 * This function is a no-op if the VTL mode is not enabled.
 66	 * If it is, this function runs if and only the kernel boots in
 67	 * VTL2 which the x86 hv initialization path makes sure of.
 68	 */
 69	pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);
 70
 71	x86_platform.realmode_reserve = x86_init_noop;
 72	x86_platform.realmode_init = x86_init_noop;
 73	x86_init.irqs.pre_vector_init = x86_init_noop;
 74	x86_init.timers.timer_init = x86_init_noop;
 75	x86_init.resources.probe_roms = x86_init_noop;
 76
 77	/* Avoid searching for BIOS MP tables */
 78	x86_init.mpparse.find_mptable = x86_init_noop;
 79	x86_init.mpparse.early_parse_smp_cfg = x86_init_noop;
 80
 81	x86_platform.get_wallclock = get_rtc_noop;
 82	x86_platform.set_wallclock = set_rtc_noop;
 83	x86_platform.get_nmi_reason = hv_get_nmi_reason;
 84
 85	x86_platform.legacy.i8042 = X86_LEGACY_I8042_PLATFORM_ABSENT;
 86	x86_platform.legacy.rtc = 0;
 87	x86_platform.legacy.warm_reset = 0;
 88	x86_platform.legacy.reserve_bios_regions = 0;
 89	x86_platform.legacy.devices.pnpbios = 0;
 90
 91	x86_init.hyper.msi_ext_dest_id = hv_vtl_msi_ext_dest_id;
 92}
 93
 94static inline u64 hv_vtl_system_desc_base(struct ldttss_desc *desc)
 95{
 96	return ((u64)desc->base3 << 32) | ((u64)desc->base2 << 24) |
 97		(desc->base1 << 16) | desc->base0;
 98}
 99
100static inline u32 hv_vtl_system_desc_limit(struct ldttss_desc *desc)
101{
102	return ((u32)desc->limit1 << 16) | (u32)desc->limit0;
103}
104
105typedef void (*secondary_startup_64_fn)(void*, void*);
106static void hv_vtl_ap_entry(void)
107{
108	((secondary_startup_64_fn)secondary_startup_64)(&boot_params, &boot_params);
109}
110
111static int hv_vtl_bringup_vcpu(u32 target_vp_index, int cpu, u64 eip_ignored)
112{
113	u64 status, rsp, rip;
114	int ret = 0;
115	struct hv_enable_vp_vtl *input;
116	unsigned long irq_flags;
117
118	struct desc_ptr gdt_ptr;
119	struct desc_ptr idt_ptr;
120
121	struct ldttss_desc *tss;
122	struct ldttss_desc *ldt;
123	struct desc_struct *gdt;
124
125	struct task_struct *idle = idle_thread_get(cpu);
126	if (IS_ERR(idle))
127		return PTR_ERR(idle);
128
129	rsp = (unsigned long)idle->thread.sp;
130	rip = (u64)&hv_vtl_ap_entry;
131
132	native_store_gdt(&gdt_ptr);
133	store_idt(&idt_ptr);
134
135	gdt = (struct desc_struct *)((void *)(gdt_ptr.address));
136	tss = (struct ldttss_desc *)(gdt + GDT_ENTRY_TSS);
137	ldt = (struct ldttss_desc *)(gdt + GDT_ENTRY_LDT);
138
139	local_irq_save(irq_flags);
140
141	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
142	memset(input, 0, sizeof(*input));
143
144	input->partition_id = HV_PARTITION_ID_SELF;
145	input->vp_index = target_vp_index;
146	input->target_vtl.target_vtl = HV_VTL_MGMT;
147
148	/*
149	 * The x86_64 Linux kernel follows the 16-bit -> 32-bit -> 64-bit
150	 * mode transition sequence after waking up an AP with SIPI whose
151	 * vector points to the 16-bit AP startup trampoline code. Here in
152	 * VTL2, we can't perform that sequence as the AP has to start in
153	 * the 64-bit mode.
154	 *
155	 * To make this happen, we tell the hypervisor to load a valid 64-bit
156	 * context (most of which is just magic numbers from the CPU manual)
157	 * so that AP jumps right to the 64-bit entry of the kernel, and the
158	 * control registers are loaded with values that let the AP fetch the
159	 * code and data and carry on with work it gets assigned.
160	 */
161
162	input->vp_context.rip = rip;
163	input->vp_context.rsp = rsp;
164	input->vp_context.rflags = 0x0000000000000002;
165	input->vp_context.efer = native_rdmsrq(MSR_EFER);
166	input->vp_context.cr0 = native_read_cr0();
167	input->vp_context.cr3 = __native_read_cr3();
168	input->vp_context.cr4 = native_read_cr4();
169	input->vp_context.msr_cr_pat = native_rdmsrq(MSR_IA32_CR_PAT);
170	input->vp_context.idtr.limit = idt_ptr.size;
171	input->vp_context.idtr.base = idt_ptr.address;
172	input->vp_context.gdtr.limit = gdt_ptr.size;
173	input->vp_context.gdtr.base = gdt_ptr.address;
174
175	/* Non-system desc (64bit), long, code, present */
176	input->vp_context.cs.selector = __KERNEL_CS;
177	input->vp_context.cs.base = 0;
178	input->vp_context.cs.limit = 0xffffffff;
179	input->vp_context.cs.attributes = 0xa09b;
180	/* Non-system desc (64bit), data, present, granularity, default */
181	input->vp_context.ss.selector = __KERNEL_DS;
182	input->vp_context.ss.base = 0;
183	input->vp_context.ss.limit = 0xffffffff;
184	input->vp_context.ss.attributes = 0xc093;
185
186	/* System desc (128bit), present, LDT */
187	input->vp_context.ldtr.selector = GDT_ENTRY_LDT * 8;
188	input->vp_context.ldtr.base = hv_vtl_system_desc_base(ldt);
189	input->vp_context.ldtr.limit = hv_vtl_system_desc_limit(ldt);
190	input->vp_context.ldtr.attributes = 0x82;
191
192	/* System desc (128bit), present, TSS, 0x8b - busy, 0x89 -- default */
193	input->vp_context.tr.selector = GDT_ENTRY_TSS * 8;
194	input->vp_context.tr.base = hv_vtl_system_desc_base(tss);
195	input->vp_context.tr.limit = hv_vtl_system_desc_limit(tss);
196	input->vp_context.tr.attributes = 0x8b;
197
198	status = hv_do_hypercall(HVCALL_ENABLE_VP_VTL, input, NULL);
199
200	if (!hv_result_success(status) &&
201	    hv_result(status) != HV_STATUS_VTL_ALREADY_ENABLED) {
202		pr_err("HVCALL_ENABLE_VP_VTL failed for VP : %d ! [Err: %#llx\n]",
203		       target_vp_index, status);
204		ret = -EINVAL;
205		goto free_lock;
206	}
207
208	status = hv_do_hypercall(HVCALL_START_VP, input, NULL);
209
210	if (!hv_result_success(status)) {
211		pr_err("HVCALL_START_VP failed for VP : %d ! [Err: %#llx]\n",
212		       target_vp_index, status);
213		ret = -EINVAL;
214	}
215
216free_lock:
217	local_irq_restore(irq_flags);
218
219	return ret;
220}
221
222static int hv_vtl_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip, unsigned int cpu)
223{
224	int vp_index;
225
226	pr_debug("Bringing up CPU with APIC ID %d in VTL2...\n", apicid);
227	vp_index = hv_apicid_to_vp_index(apicid);
228
229	if (vp_index < 0) {
230		pr_err("Couldn't find CPU with APIC ID %d\n", apicid);
231		return -EINVAL;
232	}
233	if (vp_index > ms_hyperv.max_vp_index) {
234		pr_err("Invalid CPU id %d for APIC ID %d\n", vp_index, apicid);
235		return -EINVAL;
236	}
237
238	return hv_vtl_bringup_vcpu(vp_index, cpu, start_eip);
239}
240
241int __init hv_vtl_early_init(void)
242{
243	machine_ops.emergency_restart = hv_vtl_emergency_restart;
244	machine_ops.restart = hv_vtl_restart;
245
246	/*
247	 * `boot_cpu_has` returns the runtime feature support,
248	 * and here is the earliest it can be used.
249	 */
250	if (cpu_feature_enabled(X86_FEATURE_XSAVE))
251		panic("XSAVE has to be disabled as it is not supported by this module.\n"
252			  "Please add 'noxsave' to the kernel command line.\n");
253
254	real_mode_header = &hv_vtl_real_mode_header;
255	apic_update_callback(wakeup_secondary_cpu_64, hv_vtl_wakeup_secondary_cpu);
256
257	return 0;
258}
259
260DEFINE_STATIC_CALL_NULL(__mshv_vtl_return_hypercall, void (*)(void));
261
262void mshv_vtl_return_call_init(u64 vtl_return_offset)
263{
264	static_call_update(__mshv_vtl_return_hypercall,
265			   (void *)((u8 *)hv_hypercall_pg + vtl_return_offset));
266}
267EXPORT_SYMBOL(mshv_vtl_return_call_init);
268
269void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
270{
271	struct hv_vp_assist_page *hvp;
272
273	hvp = hv_vp_assist_page[smp_processor_id()];
274	hvp->vtl_ret_x64rax = vtl0->rax;
275	hvp->vtl_ret_x64rcx = vtl0->rcx;
276
277	kernel_fpu_begin_mask(0);
278	fxrstor(&vtl0->fx_state);
279	__mshv_vtl_return_call(vtl0);
280	fxsave(&vtl0->fx_state);
281	kernel_fpu_end();
282}
283EXPORT_SYMBOL(mshv_vtl_return_call);