KVM: Flush remote tlbs when reducing shadow pte permissions

When a vcpu causes a shadow tlb entry to have reduced permissions, it
must also clear the tlb on remote vcpus.  We do that by:

- setting a bit on the vcpu that requests a tlb flush before the next entry
- if the vcpu is currently executing, we send an ipi to make sure it
  exits before we continue

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 4e1a017f3db7..633c2eded08d 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -41,6 +41,8 @@
 #include <linux/fs.h>
 #include <linux/mount.h>
 #include <linux/sched.h>
+#include <linux/cpumask.h>
+#include <linux/smp.h>
 
 #include "x86_emulate.h"
 #include "segment_descriptor.h"
@@ -309,6 +311,48 @@ static void vcpu_put(struct kvm_vcpu *vcpu)
         mutex_unlock(&vcpu->mutex);
 }
 
+static void ack_flush(void *_completed)
+{
+        atomic_t *completed = _completed;
+
+        atomic_inc(completed);
+}
+
+void kvm_flush_remote_tlbs(struct kvm *kvm)
+{
+        int i, cpu, needed;
+        cpumask_t cpus;
+        struct kvm_vcpu *vcpu;
+        atomic_t completed;
+
+        atomic_set(&completed, 0);
+        cpus_clear(cpus);
+        needed = 0;
+        for (i = 0; i < kvm->nvcpus; ++i) {
+                vcpu = &kvm->vcpus[i];
+                if (test_and_set_bit(KVM_TLB_FLUSH, &vcpu->requests))
+                        continue;
+                cpu = vcpu->cpu;
+                if (cpu != -1 && cpu != raw_smp_processor_id())
+                        if (!cpu_isset(cpu, cpus)) {
+                                cpu_set(cpu, cpus);
+                                ++needed;
+                        }
+        }
+
+        /*
+         * We really want smp_call_function_mask() here.  But that's not
+         * available, so ipi all cpus in parallel and wait for them
+         * to complete.
+         */
+        for (cpu = first_cpu(cpus); cpu != NR_CPUS; cpu = next_cpu(cpu, cpus))
+                smp_call_function_single(cpu, ack_flush, &completed, 1, 0);
+        while (atomic_read(&completed) != needed) {
+                cpu_relax();
+                barrier();
+        }
+}
+
 static struct kvm *kvm_create_vm(void)
 {
         struct kvm *kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);