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 /* 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() */ 76 void 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 } 94