[PATCH v12 09/18] KVM: s390: pv: add mmu_notifier

[Claudio Imbrenda]

Add an mmu_notifier for protected VMs. The callback function is
triggered when the mm is torn down, and will attempt to convert all
protected vCPUs to non-protected. This allows the mm teardown to use
the destroy page UVC instead of export.

Also make KVM select CONFIG_MMU_NOTIFIER, needed to use mmu_notifiers.

Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Acked-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
Reviewed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
---
 arch/s390/include/asm/kvm_host.h |  2 ++
 arch/s390/kvm/Kconfig            |  1 +
 arch/s390/kvm/kvm-s390.c         | 10 ++++++++++
 arch/s390/kvm/pv.c               | 26 ++++++++++++++++++++++++++
 4 files changed, 39 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 766028d54a3e..5824efe5fc9d 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -19,6 +19,7 @@
 #include <linux/kvm.h>
 #include <linux/seqlock.h>
 #include <linux/module.h>
+#include <linux/mmu_notifier.h>
 #include <asm/debug.h>
 #include <asm/cpu.h>
 #include <asm/fpu/api.h>
@@ -923,6 +924,7 @@ struct kvm_s390_pv {
 	u64 guest_len;
 	unsigned long stor_base;
 	void *stor_var;
+	struct mmu_notifier mmu_notifier;
 };
 
 struct kvm_arch{
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index 2e84d3922f7c..33f4ff909476 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -34,6 +34,7 @@ config KVM
 	select SRCU
 	select KVM_VFIO
 	select INTERVAL_TREE
+	select MMU_NOTIFIER
 	help
 	  Support hosting paravirtualized guest machines using the SIE
 	  virtualization capability on the mainframe. This should work
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 40e61631b13d..6b63e0605a51 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -31,6 +31,7 @@
 #include <linux/sched/signal.h>
 #include <linux/string.h>
 #include <linux/pgtable.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/asm-offsets.h>
 #include <asm/lowcore.h>
@@ -2928,6 +2929,15 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 	 */
 	if (kvm_s390_pv_get_handle(kvm))
 		kvm_s390_pv_deinit_vm(kvm, &rc, &rrc);
+	/*
+	 * Remove the mmu notifier only when the whole KVM VM is torn down,
+	 * and only if one was registered to begin with. If the VM is
+	 * currently not protected, but has been previously been protected,
+	 * then it's possible that the notifier is still registered.
+	 */
+	if (kvm->arch.pv.mmu_notifier.ops)
+		mmu_notifier_unregister(&kvm->arch.pv.mmu_notifier, kvm->mm);
+
 	debug_unregister(kvm->arch.dbf);
 	free_page((unsigned long)kvm->arch.sie_page2);
 	if (!kvm_is_ucontrol(kvm))
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index 9eca80afedce..da1bae111fb1 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -14,6 +14,7 @@
 #include <asm/mman.h>
 #include <linux/pagewalk.h>
 #include <linux/sched/mm.h>
+#include <linux/mmu_notifier.h>
 #include "kvm-s390.h"
 
 static void kvm_s390_clear_pv_state(struct kvm *kvm)
@@ -187,6 +188,26 @@ int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
 	return -EIO;
 }
 
+static void kvm_s390_pv_mmu_notifier_release(struct mmu_notifier *subscription,
+					     struct mm_struct *mm)
+{
+	struct kvm *kvm = container_of(subscription, struct kvm, arch.pv.mmu_notifier);
+	u16 dummy;
+
+	/*
+	 * No locking is needed since this is the last thread of the last user of this
+	 * struct mm.
+	 * When the struct kvm gets deinitialized, this notifier is also
+	 * unregistered. This means that if this notifier runs, then the
+	 * struct kvm is still valid.
+	 */
+	kvm_s390_cpus_from_pv(kvm, &dummy, &dummy);
+}
+
+static const struct mmu_notifier_ops kvm_s390_pv_mmu_notifier_ops = {
+	.release = kvm_s390_pv_mmu_notifier_release,
+};
+
 int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
 {
 	struct uv_cb_cgc uvcb = {
@@ -228,6 +249,11 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
 		return -EIO;
 	}
 	kvm->arch.gmap->guest_handle = uvcb.guest_handle;
+	/* Add the notifier only once. No races because we hold kvm->lock */
+	if (kvm->arch.pv.mmu_notifier.ops != &kvm_s390_pv_mmu_notifier_ops) {
+		kvm->arch.pv.mmu_notifier.ops = &kvm_s390_pv_mmu_notifier_ops;
+		mmu_notifier_register(&kvm->arch.pv.mmu_notifier, kvm->mm);
+	}
 	return 0;
 }
 
-- 
2.36.1