[RFC PATCH 5/8] svm: Add support for APIC_ACCESS_PAGE_PRIVATE_MEMSLOT setup/destroy

["Suthikulpanit, Suravee" <Suravee.Suthikulpanit@xxxxxxx>]

Activate/deactivate AVIC requires setting/unsetting the memory region used
for APIC_ACCESS_PAGE_PRIVATE_MEMSLOT. So, re-factor avic_init_access_page()
to avic_setup_access_page() and add srcu_read_lock/unlock, which are needed
to allow this function to be called during run-time.

Also, introduce avic_destroy_access_page() to unset the page when
deactivate AVIC.

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 arch/x86/kvm/svm.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index c33f02b4a19e..a23b1e77acb6 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1658,7 +1658,7 @@ static u64 *avic_get_physical_id_entry(struct kvm_vcpu *vcpu,
  * field of the VMCB. Therefore, we set up the
  * APIC_ACCESS_PAGE_PRIVATE_MEMSLOT (4KB) here.
  */
-static int avic_init_access_page(struct kvm_vcpu *vcpu)
+static int avic_setup_access_page(struct kvm_vcpu *vcpu, bool init)
 {
 	struct kvm *kvm = vcpu->kvm;
 	int ret = 0;
@@ -1667,10 +1667,14 @@ static int avic_init_access_page(struct kvm_vcpu *vcpu)
 	if (kvm->arch.apic_access_page_done)
 		goto out;
 
+	if (!init)
+		srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
 	ret = __x86_set_memory_region(kvm,
 				      APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
 				      APIC_DEFAULT_PHYS_BASE,
 				      PAGE_SIZE);
+	if (!init)
+		vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
 	if (ret)
 		goto out;
 
@@ -1680,6 +1684,26 @@ static int avic_init_access_page(struct kvm_vcpu *vcpu)
 	return ret;
 }
 
+static void avic_destroy_access_page(struct kvm_vcpu *vcpu)
+{
+	struct kvm *kvm = vcpu->kvm;
+
+	mutex_lock(&kvm->slots_lock);
+
+	if (!kvm->arch.apic_access_page_done)
+		goto out;
+
+	srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+	__x86_set_memory_region(kvm,
+				APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
+				APIC_DEFAULT_PHYS_BASE,
+				0);
+	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+	kvm->arch.apic_access_page_done = false;
+out:
+	mutex_unlock(&kvm->slots_lock);
+}
+
 static int avic_init_backing_page(struct kvm_vcpu *vcpu)
 {
 	int ret;
@@ -1687,7 +1711,7 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
 	int id = vcpu->vcpu_id;
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	ret = avic_init_access_page(vcpu);
+	ret = avic_setup_access_page(vcpu, true);
 	if (ret)
 		return ret;
 
-- 
2.17.1