[PATCH v4 1/2] x86/kexec: VMCLEAR vmcss on all cpus if necessary

[zhangyanfei]

crash_clear_loaded_vmcss is added to VMCLEAR vmcss loaded on all
cpus. And when loading kvm_intel module, the function pointer will be
made valid.
The percpu variable vmclear_skipped is added to flag the case that
if loaded_vmcss_on_cpu list is being modified while the machine crashes
and doing kdump, the vmclear here can be skipped.

Signed-off-by: Zhang Yanfei <zhangyanfei at cn.fujitsu.com>
---
 arch/x86/include/asm/kexec.h |    3 +++
 arch/x86/kernel/crash.c      |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index 317ff17..d892211 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -163,6 +163,9 @@ struct kimage_arch {
 };
 #endif
 
+extern void (*crash_clear_loaded_vmcss)(void);
+DECLARE_PER_CPU(int, vmclear_skipped);
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_KEXEC_H */
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 13ad899..b9f264e 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -16,6 +16,7 @@
 #include <linux/delay.h>
 #include <linux/elf.h>
 #include <linux/elfcore.h>
+#include <linux/module.h>
 
 #include <asm/processor.h>
 #include <asm/hardirq.h>
@@ -30,6 +31,27 @@
 
 int in_crash_kexec;
 
+/*
+ * This is used to VMCLEAR vmcss loaded on all
+ * cpus. And when loading kvm_intel module, the
+ * function pointer will be made valid.
+ */
+void (*crash_clear_loaded_vmcss)(void) = NULL;
+EXPORT_SYMBOL_GPL(crash_clear_loaded_vmcss);
+
+DEFINE_PER_CPU(int, vmclear_skipped) = 1;
+EXPORT_SYMBOL_GPL(vmclear_skipped);
+
+static void cpu_emergency_clear_loaded_vmcss(void)
+{
+	int cpu = raw_smp_processor_id();
+	int skipped;
+
+	skipped = per_cpu(vmclear_skipped, cpu);
+	if (!skipped && crash_clear_loaded_vmcss)
+		crash_clear_loaded_vmcss();
+}
+
 #if defined(CONFIG_SMP) && defined(CONFIG_X86_LOCAL_APIC)
 
 static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
@@ -46,6 +68,11 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
 #endif
 	crash_save_cpu(regs, cpu);
 
+	/*
+	 * VMCLEAR vmcss loaded on all cpus if needed.
+	 */
+	cpu_emergency_clear_loaded_vmcss();
+
 	/* Disable VMX or SVM if needed.
 	 *
 	 * We need to disable virtualization on all CPUs.
@@ -88,6 +115,11 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 
 	kdump_nmi_shootdown_cpus();
 
+	/*
+	 * VMCLEAR vmcss loaded on this cpu if needed.
+	 */
+	cpu_emergency_clear_loaded_vmcss();
+
 	/* Booting kdump kernel with VMX or SVM enabled won't work,
 	 * because (among other limitations) we can't disable paging
 	 * with the virt flags.
-- 
1.7.1