Commit-ID: f7113ffa3bcd630066119723f539db75a5721c88 Gitweb: http://git.kernel.org/tip/f7113ffa3bcd630066119723f539db75a5721c88 Author: Andy Lutomirski <l...@amacapital.net> AuthorDate: Tue, 10 Mar 2015 11:06:00 -0700 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Mon, 16 Mar 2015 11:05:36 +0100
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 <l...@amacapital.net> Cc: Borislav Petkov <b...@alien8.de> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Oleg Nesterov <o...@redhat.com> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/b7efc1b7364039824776f68e9ddee9ec1500e894.1426009661.git.l...@amacapital.net Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/include/asm/processor.h | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index aed6d4f..c3a037b 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
