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/tlbflush.h>
 7#include <asm/traps.h>
 8
 9/* #DB in the kernel would imply the use of a kernel debugger. */
10#define FRED_DB_STACK_LEVEL		1UL
11#define FRED_NMI_STACK_LEVEL		2UL
12#define FRED_MC_STACK_LEVEL		2UL
13/*
14 * #DF is the highest level because a #DF means "something went wrong
15 * *while delivering an exception*." The number of cases for which that
16 * can happen with FRED is drastically reduced and basically amounts to
17 * "the stack you pointed me to is broken." Thus, always change stacks
18 * on #DF, which means it should be at the highest level.
19 */
20#define FRED_DF_STACK_LEVEL		3UL
21
22#define FRED_STKLVL(vector, lvl)	((lvl) << (2 * (vector)))
23
24void cpu_init_fred_exceptions(void)
25{
26	/* When FRED is enabled by default, remove this log message */
27	pr_info("Initialize FRED on CPU%d\n", smp_processor_id());
28
29	wrmsrl(MSR_IA32_FRED_CONFIG,
30	       /* Reserve for CALL emulation */
31	       FRED_CONFIG_REDZONE |
32	       FRED_CONFIG_INT_STKLVL(0) |
33	       FRED_CONFIG_ENTRYPOINT(asm_fred_entrypoint_user));
34
35	/*
36	 * The purpose of separate stacks for NMI, #DB and #MC *in the kernel*
37	 * (remember that user space faults are always taken on stack level 0)
38	 * is to avoid overflowing the kernel stack.
39	 */
40	wrmsrl(MSR_IA32_FRED_STKLVLS,
41	       FRED_STKLVL(X86_TRAP_DB,  FRED_DB_STACK_LEVEL) |
42	       FRED_STKLVL(X86_TRAP_NMI, FRED_NMI_STACK_LEVEL) |
43	       FRED_STKLVL(X86_TRAP_MC,  FRED_MC_STACK_LEVEL) |
44	       FRED_STKLVL(X86_TRAP_DF,  FRED_DF_STACK_LEVEL));
45
46	/* The FRED equivalents to IST stacks... */
47	wrmsrl(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB));
48	wrmsrl(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI));
49	wrmsrl(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF));
50
51	/* Enable FRED */
52	cr4_set_bits(X86_CR4_FRED);
53	/* Any further IDT use is a bug */
54	idt_invalidate();
55
56	/* Use int $0x80 for 32-bit system calls in FRED mode */
57	setup_clear_cpu_cap(X86_FEATURE_SYSENTER32);
58	setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
59}