[PATCH 29/45] kvm/vmx: Use get/put_online_cpus_atomic() to prevent CPU offline

[Srivatsa S. Bhat]

Once stop_machine() is gone from the CPU offline path, we won't be able
to depend on disabling preemption to prevent CPUs from going offline
from under us.

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.

Cc: Gleb Natapov <gleb at redhat.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: x86 at kernel.org
Cc: kvm at vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat at linux.vnet.ibm.com>
---

 arch/x86/kvm/vmx.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 260a919..4e1e966 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -26,6 +26,7 @@
 #include <linux/mm.h>
 #include <linux/highmem.h>
 #include <linux/sched.h>
+#include <linux/cpu.h>
 #include <linux/moduleparam.h>
 #include <linux/mod_devicetable.h>
 #include <linux/ftrace_event.h>
@@ -7164,12 +7165,12 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 	if (!vmm_exclusive)
 		kvm_cpu_vmxoff();
 
-	cpu = get_cpu();
+	cpu = get_online_cpus_atomic();
 	vmx_vcpu_load(&vmx->vcpu, cpu);
 	vmx->vcpu.cpu = cpu;
 	err = vmx_vcpu_setup(vmx);
 	vmx_vcpu_put(&vmx->vcpu);
-	put_cpu();
+	put_online_cpus_atomic();
 	if (err)
 		goto free_vmcs;
 	if (vm_need_virtualize_apic_accesses(kvm)) {
@@ -7706,12 +7707,12 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 
 	vmx->nested.vmcs01_tsc_offset = vmcs_read64(TSC_OFFSET);
 
-	cpu = get_cpu();
+	cpu = get_online_cpus_atomic();
 	vmx->loaded_vmcs = vmcs02;
 	vmx_vcpu_put(vcpu);
 	vmx_vcpu_load(vcpu, cpu);
 	vcpu->cpu = cpu;
-	put_cpu();
+	put_online_cpus_atomic();
 
 	vmx_segment_cache_clear(vmx);
 
@@ -8023,12 +8024,12 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu)
 	leave_guest_mode(vcpu);
 	prepare_vmcs12(vcpu, vmcs12);
 
-	cpu = get_cpu();
+	cpu = get_online_cpus_atomic();
 	vmx->loaded_vmcs = &vmx->vmcs01;
 	vmx_vcpu_put(vcpu);
 	vmx_vcpu_load(vcpu, cpu);
 	vcpu->cpu = cpu;
-	put_cpu();
+	put_online_cpus_atomic();
 
 	vmx_segment_cache_clear(vmx);