Module Name: src
Committed By: maxv
Date: Fri Mar 24 18:03:32 UTC 2017
Modified Files:
src/sys/arch/amd64/amd64: amd64_trap.S
Log Message:
Unconditionnally save the segment registers - because we could have a
kernel %gs and a userland %es/%ds -, and explain why T_NMI is a special
case.
Note that checking %gs directly is not a good idea: recent CPUs have the
FSGSBASE instruction set, which allows userland to directly modify %gs
without going through the kernel. If we ever enable this set, we will have
to change this function, since we won't be able to test %gs against
VM_MIN_KERNEL_ADDRESS anymore.
To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 src/sys/arch/amd64/amd64/amd64_trap.S
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/amd64/amd64/amd64_trap.S
diff -u src/sys/arch/amd64/amd64/amd64_trap.S:1.4 src/sys/arch/amd64/amd64/amd64_trap.S:1.5
--- src/sys/arch/amd64/amd64/amd64_trap.S:1.4 Sun Aug 7 09:04:55 2016
+++ src/sys/arch/amd64/amd64/amd64_trap.S Fri Mar 24 18:03:32 2017
@@ -1,4 +1,4 @@
-/* $NetBSD: amd64_trap.S,v 1.4 2016/08/07 09:04:55 maxv Exp $ */
+/* $NetBSD: amd64_trap.S,v 1.5 2017/03/24 18:03:32 maxv Exp $ */
/*-
* Copyright (c) 1998, 2007, 2008 The NetBSD Foundation, Inc.
@@ -66,7 +66,7 @@
#if 0
#include <machine/asm.h>
-__KERNEL_RCSID(0, "$NetBSD: amd64_trap.S,v 1.4 2016/08/07 09:04:55 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: amd64_trap.S,v 1.5 2017/03/24 18:03:32 maxv Exp $");
#endif
/*
@@ -103,39 +103,54 @@ IDTVEC(trap01)
ZTRAP(T_TRCTRAP)
IDTVEC_END(trap01)
+/*
+ * Non Maskable Interrupts are a special case: they can be triggered even
+ * with interrupts disabled, and once triggered they block further NMIs
+ * until an 'iret' instruction is executed.
+ *
+ * Therefore we don't enable interrupts, because the CPU could switch to
+ * another LWP, call 'iret' and unintentionally leave the NMI mode.
+ *
+ * We need to be careful about %gs too, because it is possible that we were
+ * running in kernel mode with a userland %gs.
+ */
IDTVEC(trap02)
#if defined(XEN)
ZTRAP(T_NMI)
-#else /* defined(XEN) */
- pushq $0
- pushq $T_NMI
+#else
+ pushq $0
+ pushq $T_NMI
subq $TF_REGSIZE,%rsp
INTR_SAVE_GPRS
- movl $MSR_GSBASE,%ecx
- rdmsr
- cmpl $VM_MIN_KERNEL_ADDRESS_HIGH32,%edx
- jae 1f
- swapgs
movw %gs,TF_GS(%rsp)
movw %fs,TF_FS(%rsp)
movw %es,TF_ES(%rsp)
movw %ds,TF_DS(%rsp)
+
+ movl $MSR_GSBASE,%ecx
+ rdmsr
+ cmpl $VM_MIN_KERNEL_ADDRESS_HIGH32,%edx
+ jae noswapgs
+
+ swapgs
movq %rsp,%rdi
incq CPUVAR(NTRAP)
call _C_LABEL(trap)
- movw TF_ES(%rsp),%es
- movw TF_DS(%rsp),%ds
swapgs
- jmp 2f
-1:
+ jmp nmileave
+
+noswapgs:
movq %rsp,%rdi
incq CPUVAR(NTRAP)
call _C_LABEL(trap)
-2:
+
+nmileave:
+ movw TF_ES(%rsp),%es
+ movw TF_DS(%rsp),%ds
INTR_RESTORE_GPRS
addq $TF_REGSIZE+16,%rsp
iretq
-#endif /* defined(XEN) */
+#endif
IDTVEC_END(trap02)
IDTVEC(trap03)
