[PATCH 2/4] KVM: arm64: Allow saving vgic3 pending tables in no running vcpu context

[Gavin Shan]

It's possible to save vgic3 pending tables in no running VCPU
context. This is another unknown case detected by 'kvm-unit-tests'.

   # ./kvm-unit-tests/tests/its-pending-migration
   WARNING: CPU: 120 PID: 7973 at arch/arm64/kvm/../../../virt/kvm/kvm_main.c:3325 \
   mark_page_dirty_in_slot+0x60/0xe0
    :
   mark_page_dirty_in_slot+0x60/0xe0
   __kvm_write_guest_page+0xcc/0x100
   kvm_write_guest+0x7c/0xb0
   vgic_v3_save_pending_tables+0x148/0x2a0
   vgic_set_common_attr+0x158/0x240
   vgic_v3_set_attr+0x4c/0x5c
   kvm_device_ioctl+0x100/0x160
   __arm64_sys_ioctl+0xa8/0xf0
   invoke_syscall.constprop.0+0x7c/0xd0
   el0_svc_common.constprop.0+0x144/0x160
   do_el0_svc+0x34/0x60
   el0_svc+0x3c/0x1a0
   el0t_64_sync_handler+0xb4/0x130
   el0t_64_sync+0x178/0x17c

Fix it by allowing to save VGIC3 pending tables in no running VCPU
context.

Reported-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
---
 Documentation/virt/kvm/api.rst | 3 +++
 arch/arm64/kvm/vgic/vgic-v3.c  | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 18b245a0ba02..7cf3d4b77703 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8074,6 +8074,9 @@ NOTE: One example of using the backup bitmap is saving arm64 vgic/its
 tables and vgic3 LPI pending status through KVM_DEV_ARM_{VGIC_GRP_CTRL,
 ITS_SAVE_TABLES} and KVM_DEV_ARM_{VGIC_GRP_CTRL, ITS_RESTORE_TABLES}
 command on KVM device "kvm-arm-vgic-its" when dirty ring is enabled.
+The backup bitmap is also used when vgic3 pending table is saved
+through KVM_DEV_ARM_{VGIC_GRP_CTRL, VGIC_SAVE_PENDING_TABLES} command
+on KVM device "kvm-arm-vgic-v3".
 
 8.30 KVM_CAP_XEN_HVM
 --------------------
diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index 32998c8587a8..1e6b5f19d524 100644
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -440,7 +440,9 @@ int vgic_v3_save_pending_tables(struct kvm *kvm)
 		else
 			val &= ~(1 << bit_nr);
 
+		dist->save_vgic_v3_tables_in_progress = true;
 		ret = kvm_write_guest_lock(kvm, ptr, &val, 1);
+		dist->save_vgic_v3_tables_in_progress = false;
 		if (ret)
 			goto out;
 	}
-- 
2.23.0