diff options
| -rw-r--r-- | arch/x86/include/asm/processor.h | 22 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/common.c | 9 |
2 files changed, 16 insertions, 15 deletions
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 572099710ba2..d2203b5d9538 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -209,21 +209,21 @@ struct x86_hw_tss { unsigned short back_link, __blh; unsigned long sp0; unsigned short ss0, __ss0h; + unsigned long sp1; /* - * We don't use ring 1, so sp1 and ss1 are convenient scratch - * spaces in the same cacheline as sp0. We use them to cache - * some MSR values to avoid unnecessary wrmsr instructions. + * We don't use ring 1, so ss1 is a convenient scratch space in + * the same cacheline as sp0. We use ss1 to cache the value in + * MSR_IA32_SYSENTER_CS. When we context switch + * MSR_IA32_SYSENTER_CS, we first check if the new value being + * written matches ss1, and, if it's not, then we wrmsr the new + * value and update ss1. * - * We use SYSENTER_ESP to find sp0 and for the NMI emergency - * stack, but we need to context switch it because we do - * horrible things to the kernel stack in vm86 mode. - * - * We use SYSENTER_CS to disable sysenter in vm86 mode to avoid - * corrupting the stack if we went through the sysenter path - * from vm86 mode. + * The only reason we context switch MSR_IA32_SYSENTER_CS is + * that we set it to zero in vm86 tasks to avoid corrupting the + * stack if we were to go through the sysenter path from vm86 + * mode. */ - unsigned long sp1; /* MSR_IA32_SYSENTER_ESP */ unsigned short ss1; /* MSR_IA32_SYSENTER_CS */ unsigned short __ss1h; diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 71e4adcb15f1..a383d53bf0ed 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -976,15 +976,16 @@ void enable_sep_cpu(void) goto out; /* - * The struct::SS1 and tss_struct::SP1 fields are not used by the hardware, - * we cache the SYSENTER CS and ESP values there for easy access: + * We cache MSR_IA32_SYSENTER_CS's value in the TSS's ss1 field -- + * see the big comment in struct x86_hw_tss's definition. */ tss->x86_tss.ss1 = __KERNEL_CS; wrmsr(MSR_IA32_SYSENTER_CS, tss->x86_tss.ss1, 0); - tss->x86_tss.sp1 = (unsigned long)tss + offsetofend(struct tss_struct, SYSENTER_stack); - wrmsr(MSR_IA32_SYSENTER_ESP, tss->x86_tss.sp1, 0); + wrmsr(MSR_IA32_SYSENTER_ESP, + (unsigned long)tss + offsetofend(struct tss_struct, SYSENTER_stack), + 0); wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long)ia32_sysenter_target, 0); |