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Commit 76e4c490 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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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: default avatarAndy 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: default avatarIngo Molnar <mingo@kernel.org>
parent d9e05cc5

arch/x86/include/asm/processor.h

+18 −3
Original line number Diff line number Diff line
@@ -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;