From cf9328cc9989e028fdc64d8c0a7b1b043dc96735 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 2 Apr 2015 12:41:45 -0700 Subject: x86/asm/entry/32: Stop caching MSR_IA32_SYSENTER_ESP in tss.sp1 We write a stack pointer to MSR_IA32_SYSENTER_ESP exactly once, and we unnecessarily cache the value in tss.sp1. We never read the cached value. Remove all of the caching. It serves no purpose. Suggested-by: Denys Vlasenko Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/05a0163eb33ef5208363f0015496855da7cebadd.1428002830.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/processor.h | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) (limited to 'arch/x86/include/asm/processor.h') 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; -- cgit v1.2.3