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 25 DEFINE_PER_CPU(unsigned long, fred_rsp0); 26 EXPORT_PER_CPU_SYMBOL(fred_rsp0); 27 28 void 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() */ 73 void 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 } 91