1/* SPDX-License-Identifier: GPL-2.0 */
2#include <linux/kernel.h>
3
4#include <asm/desc.h>
5#include <asm/fred.h>
6#include <asm/msr.h>
7#include <asm/tlbflush.h>
8#include <asm/traps.h>
9
10/* #DB in the kernel would imply the use of a kernel debugger. */
11#define FRED_DB_STACK_LEVEL 1UL
12#define FRED_NMI_STACK_LEVEL 2UL
13#define FRED_MC_STACK_LEVEL 2UL
14/*
15 * #DF is the highest level because a #DF means "something went wrong
16 * *while delivering an exception*." The number of cases for which that
17 * can happen with FRED is drastically reduced and basically amounts to
18 * "the stack you pointed me to is broken." Thus, always change stacks
19 * on #DF, which means it should be at the highest level.
20 */
21#define FRED_DF_STACK_LEVEL 3UL
22
23#define FRED_STKLVL(vector, lvl) ((lvl) << (2 * (vector)))
24
25DEFINE_PER_CPU(unsigned long, fred_rsp0);
26EXPORT_PER_CPU_SYMBOL(fred_rsp0);
27
28void cpu_init_fred_exceptions(void)
29{
30 /* When FRED is enabled by default, remove this log message */
31 pr_info("Initialize FRED on CPU%d\n", smp_processor_id());
32
33 /*
34 * If a kernel event is delivered before a CPU goes to user level for
35 * the first time, its SS is NULL thus NULL is pushed into the SS field
36 * of the FRED stack frame. But before ERETS is executed, the CPU may
37 * context switch to another task and go to user level. Then when the
38 * CPU comes back to kernel mode, SS is changed to __KERNEL_DS. Later
39 * when ERETS is executed to return from the kernel event handler, a #GP
40 * fault is generated because SS doesn't match the SS saved in the FRED
41 * stack frame.
42 *
43 * Initialize SS to __KERNEL_DS when enabling FRED to avoid such #GPs.
44 */
45 loadsegment(ss, __KERNEL_DS);
46
47 wrmsrq(MSR_IA32_FRED_CONFIG,
48 /* Reserve for CALL emulation */
49 FRED_CONFIG_REDZONE |
50 FRED_CONFIG_INT_STKLVL(0) |
51 FRED_CONFIG_ENTRYPOINT(asm_fred_entrypoint_user));
52
53 wrmsrq(MSR_IA32_FRED_STKLVLS, val: 0);
54
55 /*
56 * Ater a CPU offline/online cycle, the FRED RSP0 MSR should be
57 * resynchronized with its per-CPU cache.
58 */
59 wrmsrq(MSR_IA32_FRED_RSP0, __this_cpu_read(fred_rsp0));
60
61 wrmsrq(MSR_IA32_FRED_RSP1, val: 0);
62 wrmsrq(MSR_IA32_FRED_RSP2, val: 0);
63 wrmsrq(MSR_IA32_FRED_RSP3, val: 0);
64
65 /* Enable FRED */
66 cr4_set_bits(X86_CR4_FRED);
67 /* Any further IDT use is a bug */
68 idt_invalidate();
69
70 /* Use int $0x80 for 32-bit system calls in FRED mode */
71 setup_clear_cpu_cap(X86_FEATURE_SYSENTER32);
72 setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
73}
74
75/* Must be called after setup_cpu_entry_areas() */
76void cpu_init_fred_rsps(void)
77{
78 /*
79 * The purpose of separate stacks for NMI, #DB and #MC *in the kernel*
80 * (remember that user space faults are always taken on stack level 0)
81 * is to avoid overflowing the kernel stack.
82 */
83 wrmsrq(MSR_IA32_FRED_STKLVLS,
84 FRED_STKLVL(X86_TRAP_DB, FRED_DB_STACK_LEVEL) |
85 FRED_STKLVL(X86_TRAP_NMI, FRED_NMI_STACK_LEVEL) |
86 FRED_STKLVL(X86_TRAP_MC, FRED_MC_STACK_LEVEL) |
87 FRED_STKLVL(X86_TRAP_DF, FRED_DF_STACK_LEVEL));
88
89 /* The FRED equivalents to IST stacks... */
90 wrmsrq(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB));
91 wrmsrq(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI));
92 wrmsrq(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF));
93}
94

source code of linux/arch/x86/kernel/fred.c