diff options
| -rw-r--r-- | arch/x86/kernel/fred.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c index 99a134fcd5bf..266c69e332a4 100644 --- a/arch/x86/kernel/fred.c +++ b/arch/x86/kernel/fred.c @@ -26,6 +26,20 @@ void cpu_init_fred_exceptions(void) /* When FRED is enabled by default, remove this log message */ pr_info("Initialize FRED on CPU%d\n", smp_processor_id()); + /* + * If a kernel event is delivered before a CPU goes to user level for + * the first time, its SS is NULL thus NULL is pushed into the SS field + * of the FRED stack frame. But before ERETS is executed, the CPU may + * context switch to another task and go to user level. Then when the + * CPU comes back to kernel mode, SS is changed to __KERNEL_DS. Later + * when ERETS is executed to return from the kernel event handler, a #GP + * fault is generated because SS doesn't match the SS saved in the FRED + * stack frame. + * + * Initialize SS to __KERNEL_DS when enabling FRED to avoid such #GPs. + */ + loadsegment(ss, __KERNEL_DS); + wrmsrl(MSR_IA32_FRED_CONFIG, /* Reserve for CALL emulation */ FRED_CONFIG_REDZONE | |