* Ingo Molnar <[EMAIL PROTECTED]> wrote:
> So i think we should do the patch below - this makes reboot work even
> in atomic contexts. [...]
hm, this causes problems if KVM is not active on a VT-capable CPU: even
on CPUs with VT supported, if a VT context is not actually activated, a
vmxoff causes an invalid opcode exception. So the updated patch below
uses a slightly more sophisticated approach to avoid that problem.
Ingo
-------------------->
Subject: [patch] kvm: do VMXOFF upon reboot
From: Ingo Molnar <[EMAIL PROTECTED]>
my laptop's BIOS apparently gets confused if the kernel tries to
reboot without first turning VT context off, which results in a
hung (emergency-)reboot. So make sure this happens, right before
we reboot.
( NOTE: this is a dual-core system, but only the core where the
BIOS executes seems to be affected - the other core can have an
active VT context just fine - so we dont have to risk reboot
robustness by doing a CPU cross-call in the emergency reboot
handler. )
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
---
arch/i386/kernel/reboot.c | 16 ++++++++++++++++
arch/x86_64/kernel/reboot.c | 15 +++++++++++++++
2 files changed, 31 insertions(+)
Index: linux/arch/i386/kernel/reboot.c
===================================================================
--- linux.orig/arch/i386/kernel/reboot.c
+++ linux/arch/i386/kernel/reboot.c
@@ -318,6 +318,22 @@ void machine_shutdown(void)
void machine_emergency_restart(void)
{
+ unsigned long ecx = cpuid_ecx(1);
+
+ /*
+ * Disable any possibly active VT context (if VT supported):
+ */
+ if (test_bit(5, &ecx)) { /* has VT support */
+ asm volatile (
+ "1: .byte 0x0f, 0x01, 0xc4 \n" /* vmxoff */
+ "2: \n"
+ ".section __ex_table,\"a\" \n"
+ " .align 4 \n"
+ " .long 1b,2b \n"
+ ".previous \n"
+ );
+ }
+
if (!reboot_thru_bios) {
if (efi_enabled) {
efi.reset_system(EFI_RESET_COLD, EFI_SUCCESS, 0, NULL);
Index: linux/arch/x86_64/kernel/reboot.c
===================================================================
--- linux.orig/arch/x86_64/kernel/reboot.c
+++ linux/arch/x86_64/kernel/reboot.c
@@ -114,8 +114,23 @@ void machine_shutdown(void)
void machine_emergency_restart(void)
{
+ unsigned long ecx = cpuid_ecx(1);
int i;
+ /*
+ * Disable any possibly active VT context (if VT supported):
+ */
+ if (test_bit(5, &ecx)) { /* has VT support */
+ asm volatile (
+ "1: .byte 0x0f, 0x01, 0xc4 \n" /* vmxoff */
+ "2: \n"
+ ".section __ex_table,\"a\" \n"
+ " .align 8 \n"
+ " .quad 1b,2b \n"
+ ".previous \n"
+ );
+ }
+
/* Tell the BIOS if we want cold or warm reboot */
*((unsigned short *)__va(0x472)) = reboot_mode;
-
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