KVM: s390: pv: add mmu_notifier

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@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Link: https://lore.kernel.org/r/20220628135619.32410-10-imbrenda@linux.ibm.com
Message-Id: <20220628135619.32410-10-imbrenda@linux.ibm.com>
[frankja@linux.ibm.com: Conflict resolution for mmu_notifier.h include
and struct kvm_s390_pv]
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index fca4fcf72a2a9129f3154bb0cdb8bc08ae72f209..6f9fc8bb0303b76c6299ca05256308dbdcd1ca82 100644 (file)
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -20,6 +20,7 @@
 #include <linux/seqlock.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/mmu_notifier.h>
 #include <asm/debug.h>
 #include <asm/cpu.h>
 #include <asm/fpu/api.h>
@@ -929,6 +930,7 @@ struct kvm_s390_pv {
        unsigned long stor_base;
        void *stor_var;
        bool dumping;
+       struct mmu_notifier mmu_notifier;
 };
 
 struct kvm_arch{

diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index 2e84d3922f7cd92938d0486b4fb3e4fe5e534d54..33f4ff909476cd25dee05fc9ea78bfb7fdf6ed4e 100644 (file)
--- 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 d10c3b163cdcdd3292a4fcd1f2e5127e18d15a4d..5b77c43fbb01d2a4e330261afbaba0177acd04c3 100644 (file)
--- 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>
@@ -3198,6 +3199,15 @@ 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 d18c5ccfa5dcb4fa4426419275113ed20adb1a99..c063d1a9cf04e66361076b3f2f47c5c2cd667ef0 100644 (file)
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -15,6 +15,7 @@
 #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)
@@ -188,6 +189,26 @@ 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 = {
@@ -229,6 +250,11 @@ 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;
 }