fred.c

 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, 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, 0);
62	wrmsrq(MSR_IA32_FRED_RSP2, 0);
63	wrmsrq(MSR_IA32_FRED_RSP3, 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}