Commit-ID: f7113ffa3bcd630066119723f539db75a5721c88
Gitweb: http://git.kernel.org/tip/f7113ffa3bcd630066119723f539db75a5721c88
Author: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
AuthorDate: Tue, 10 Mar 2015 11:06:00 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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 <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/b7efc1b7364039824776f68e9ddee9ec1500e894.1426009661.git.luto@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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;
--
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