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x86/asm/entry/32: Document our abuse of x86_hw_tss::ss1 and x86_hw_tss::sp1 

This has confused me for a while.  Now that I figured it out, document it.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/b7efc1b7364039824776f68e9ddee9ec1500e894.1426009661.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2015-03-10 11:06:00 -07:00 committed by Ingo Molnar
parent d9e05cc5a5
commit 76e4c4908a
1 changed files with 18 additions and 3 deletions
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21
arch/x86/include/asm/processor.h
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@ -209,9 +209,24 @@ struct x86_hw_tss {
unsigned short back_link, __blh;
unsigned long sp0;
unsigned short ss0, __ss0h;
unsigned long sp1;
/* ss1 caches MSR_IA32_SYSENTER_CS: */
unsigned short ss1, __ss1h;
/*
* 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 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.
*/
unsigned long sp1; /* MSR_IA32_SYSENTER_ESP */
unsigned short ss1; /* MSR_IA32_SYSENTER_CS */
unsigned short __ss1h;
unsigned long sp2;
unsigned short ss2, __ss2h;
unsigned long __cr3;