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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 /*
31 * If a kernel event is delivered before a CPU goes to user level for
32 * the first time, its SS is NULL thus NULL is pushed into the SS field
33 * of the FRED stack frame. But before ERETS is executed, the CPU may
34 * context switch to another task and go to user level. Then when the
35 * CPU comes back to kernel mode, SS is changed to __KERNEL_DS. Later
36 * when ERETS is executed to return from the kernel event handler, a #GP
37 * fault is generated because SS doesn't match the SS saved in the FRED
38 * stack frame.
39 *
40 * Initialize SS to __KERNEL_DS when enabling FRED to avoid such #GPs.
41 */
42 loadsegment(ss, __KERNEL_DS);
43
44 wrmsrq(MSR_IA32_FRED_CONFIG,
45 /* Reserve for CALL emulation */
46 FRED_CONFIG_REDZONE |
47 FRED_CONFIG_INT_STKLVL(0) |
48 FRED_CONFIG_ENTRYPOINT(asm_fred_entrypoint_user));
49
50 wrmsrq(MSR_IA32_FRED_STKLVLS, 0);
51
52 /*
53 * Ater a CPU offline/online cycle, the FRED RSP0 MSR should be
54 * resynchronized with its per-CPU cache.
55 */
56 wrmsrq(MSR_IA32_FRED_RSP0, __this_cpu_read(fred_rsp0));
57
58 wrmsrq(MSR_IA32_FRED_RSP1, 0);
59 wrmsrq(MSR_IA32_FRED_RSP2, 0);
60 wrmsrq(MSR_IA32_FRED_RSP3, 0);
61
62 /* Enable FRED */
63 cr4_set_bits(X86_CR4_FRED);
64 /* Any further IDT use is a bug */
65 idt_invalidate();
66
67 /* Use int $0x80 for 32-bit system calls in FRED mode */
68 setup_clear_cpu_cap(X86_FEATURE_SYSFAST32);
69 setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
70}
71
72/* Must be called after setup_cpu_entry_areas() */
73void cpu_init_fred_rsps(void)
74{
75 /*
76 * The purpose of separate stacks for NMI, #DB and #MC *in the kernel*
77 * (remember that user space faults are always taken on stack level 0)
78 * is to avoid overflowing the kernel stack.
79 */
80 wrmsrq(MSR_IA32_FRED_STKLVLS,
81 FRED_STKLVL(X86_TRAP_DB, FRED_DB_STACK_LEVEL) |
82 FRED_STKLVL(X86_TRAP_NMI, FRED_NMI_STACK_LEVEL) |
83 FRED_STKLVL(X86_TRAP_MC, FRED_MC_STACK_LEVEL) |
84 FRED_STKLVL(X86_TRAP_DF, FRED_DF_STACK_LEVEL));
85
86 /* The FRED equivalents to IST stacks... */
87 wrmsrq(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB));
88 wrmsrq(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI));
89 wrmsrq(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF));
90}