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| author | Andy Lutomirski <luto@amacapital.net> | 2015-03-10 21:06:00 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-03-17 11:25:27 +0300 |
| commit | 76e4c4908a4904a61aa67ae5eb0b2a7588c4a546 (patch) | |
| tree | 940da1239b6f247a94a9169d9b500dbbf0223ce3 /arch/x86/include/asm/processor.h | |
| parent | d9e05cc5a53246e074dc2b84956252e4bbe392cd (diff) | |
| download | linux-76e4c4908a4904a61aa67ae5eb0b2a7588c4a546.tar.xz | |
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>
Diffstat (limited to 'arch/x86/include/asm/processor.h')
| -rw-r--r-- | arch/x86/include/asm/processor.h | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index fc6d8d0d8d53..b26208998b7c 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -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; |