1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _ASM_X86_SWITCH_TO_H 3 #define _ASM_X86_SWITCH_TO_H 4 5 #include <linux/sched/task_stack.h> 6 7 struct task_struct; /* one of the stranger aspects of C forward declarations */ 8 9 struct task_struct *__switch_to_asm(struct task_struct *prev, 10 struct task_struct *next); 11 12 __visible struct task_struct *__switch_to(struct task_struct *prev, 13 struct task_struct *next); 14 15 /* This runs runs on the previous thread's stack. */ 16 static inline void prepare_switch_to(struct task_struct *next) 17 { 18 #ifdef CONFIG_VMAP_STACK 19 /* 20 * If we switch to a stack that has a top-level paging entry 21 * that is not present in the current mm, the resulting #PF will 22 * will be promoted to a double-fault and we'll panic. Probe 23 * the new stack now so that vmalloc_fault can fix up the page 24 * tables if needed. This can only happen if we use a stack 25 * in vmap space. 26 * 27 * We assume that the stack is aligned so that it never spans 28 * more than one top-level paging entry. 29 * 30 * To minimize cache pollution, just follow the stack pointer. 31 */ 32 READ_ONCE(*(unsigned char *)next->thread.sp); 33 #endif 34 } 35 36 asmlinkage void ret_from_fork(void); 37 38 /* 39 * This is the structure pointed to by thread.sp for an inactive task. The 40 * order of the fields must match the code in __switch_to_asm(). 41 */ 42 struct inactive_task_frame { 43 #ifdef CONFIG_X86_64 44 unsigned long r15; 45 unsigned long r14; 46 unsigned long r13; 47 unsigned long r12; 48 #else 49 unsigned long flags; 50 unsigned long si; 51 unsigned long di; 52 #endif 53 unsigned long bx; 54 55 /* 56 * These two fields must be together. They form a stack frame header, 57 * needed by get_frame_pointer(). 58 */ 59 unsigned long bp; 60 unsigned long ret_addr; 61 }; 62 63 struct fork_frame { 64 struct inactive_task_frame frame; 65 struct pt_regs regs; 66 }; 67 68 #define switch_to(prev, next, last) \ 69 do { \ 70 prepare_switch_to(next); \ 71 \ 72 ((last) = __switch_to_asm((prev), (next))); \ 73 } while (0) 74 75 #ifdef CONFIG_X86_32 76 static inline void refresh_sysenter_cs(struct thread_struct *thread) 77 { 78 /* Only happens when SEP is enabled, no need to test "SEP"arately: */ 79 if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs)) 80 return; 81 82 this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs); 83 wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0); 84 } 85 #endif 86 87 /* This is used when switching tasks or entering/exiting vm86 mode. */ 88 static inline void update_task_stack(struct task_struct *task) 89 { 90 /* sp0 always points to the entry trampoline stack, which is constant: */ 91 #ifdef CONFIG_X86_32 92 if (static_cpu_has(X86_FEATURE_XENPV)) 93 load_sp0(task->thread.sp0); 94 else 95 this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0); 96 #else 97 /* 98 * x86-64 updates x86_tss.sp1 via cpu_current_top_of_stack. That 99 * doesn't work on x86-32 because sp1 and 100 * cpu_current_top_of_stack have different values (because of 101 * the non-zero stack-padding on 32bit). 102 */ 103 if (static_cpu_has(X86_FEATURE_XENPV)) 104 load_sp0(task_top_of_stack(task)); 105 #endif 106 107 } 108 109 #endif /* _ASM_X86_SWITCH_TO_H */ 110