diff options
Diffstat (limited to 'arch/x86/include/asm/processor.h')
| -rw-r--r-- | arch/x86/include/asm/processor.h | 22 |
1 files changed, 11 insertions, 11 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; |