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Message-ID:
<176928014633.26405.12867581880963943842.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net>
Date: Sat, 24 Jan 2026 18:42:26 +0000
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: pasha.tatashin@...een.com, rppt@...nel.org, pratyush@...nel.org,
kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
decui@...rosoft.com, longli@...rosoft.com
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 3/3] mshv: Block kexec when hypervisor has pages deposited
Use the live update infrastructure to make kexec safe when Microsoft
Hypervisor is active.
The kernel cannot access hypervisor-deposited pages; any access triggers a
GPF. Until the deposited-page state can be handed over to the next kernel,
kexec must be blocked is there is any hsared state between kernel and
hypervisor.
During the freeze stage:
- Refuse the transition while VMs are running
- Withdraw all pages from L1VH host (guest pages are withdrawn
upon guest shutdown)
- Verify no deposited pages remain
Abort kexec if any of the above checks fail.
Signed-off-by: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
---
MAINTAINERS | 1
drivers/hv/Kconfig | 1
drivers/hv/Makefile | 1
drivers/hv/mshv_luo.c | 113 ++++++++++++++++++++++++++++++++++++++++++
drivers/hv/mshv_root.h | 13 +++++
drivers/hv/mshv_root_main.c | 7 +++
include/linux/kho/abi/mshv.h | 14 +++++
7 files changed, 150 insertions(+)
create mode 100644 drivers/hv/mshv_luo.c
create mode 100644 include/linux/kho/abi/mshv.h
diff --git a/MAINTAINERS b/MAINTAINERS
index 5b11839cba9d..d625a1c111e2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11756,6 +11756,7 @@ F: include/hyperv/hvgdk_mini.h
F: include/hyperv/hvhdk.h
F: include/hyperv/hvhdk_mini.h
F: include/linux/hyperv.h
+F: include/linux/kho/abi/mshv.h
F: include/net/mana
F: include/uapi/linux/hyperv.h
F: include/uapi/rdma/mana-abi.h
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 7937ac0cbd0f..94887b8b92b5 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -78,6 +78,7 @@ config MSHV_ROOT
select VIRT_XFER_TO_GUEST_WORK
select HMM_MIRROR
select MMU_NOTIFIER
+ select LIVEUPDATE
default n
help
Select this option to enable support for booting and running as root
diff --git a/drivers/hv/Makefile b/drivers/hv/Makefile
index a49f93c2d245..73258fb811eb 100644
--- a/drivers/hv/Makefile
+++ b/drivers/hv/Makefile
@@ -15,6 +15,7 @@ hv_vmbus-$(CONFIG_HYPERV_TESTING) += hv_debugfs.o
hv_utils-y := hv_util.o hv_kvp.o hv_snapshot.o hv_utils_transport.o
mshv_root-y := mshv_root_main.o mshv_synic.o mshv_eventfd.o mshv_irq.o \
mshv_root_hv_call.o mshv_portid_table.o mshv_regions.o
+mshv_root-$(CONFIG_LIVEUPDATE) += mshv_luo.o
mshv_vtl-y := mshv_vtl_main.o
# Code that must be built-in
diff --git a/drivers/hv/mshv_luo.c b/drivers/hv/mshv_luo.c
new file mode 100644
index 000000000000..eed7755fc27e
--- /dev/null
+++ b/drivers/hv/mshv_luo.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2026, Microsoft Corporation.
+ *
+ * Live update orchestration management for mshv_root module.
+ *
+ * Author: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
+ */
+
+#include <linux/errno.h>
+#include <linux/liveupdate.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/kho/abi/mshv.h>
+#include <asm/mshyperv.h>
+#include "mshv_root.h"
+
+static struct file *mshv_luo_file;
+
+static void mshv_luo_finish(struct liveupdate_file_op_args *args)
+{
+}
+
+static int mshv_luo_retrieve(struct liveupdate_file_op_args *args)
+{
+ return 0;
+}
+
+static int mshv_luo_freeze(struct liveupdate_file_op_args *args)
+{
+ if (!hash_empty(mshv_root.pt_htable)) {
+ pr_warn("mshv: Cannot perform live update while VMs are active\n");
+ return -EBUSY;
+ }
+
+ if (hv_l1vh_partition()) {
+ int err;
+
+ /* Attempt to withdraw all the deposited pages */
+ err = hv_call_withdraw_memory(U64_MAX, NUMA_NO_NODE,
+ hv_current_partition_id);
+ if (err) {
+ pr_err("mshv: Failed to withdraw memory from L1 virtualization: %d\n", err);
+ return err;
+ }
+ }
+
+ if (atomic_read(&hv_pages_deposited)) {
+ pr_warn("mshv: Cannot perform live update while pages are deposited\n");
+ return -EBUSY;
+ }
+ return 0;
+}
+
+static void mshv_luo_unpreserve(struct liveupdate_file_op_args *args)
+{
+}
+
+static int mshv_luo_preserve(struct liveupdate_file_op_args *args)
+{
+ return 0;
+}
+
+static bool mshv_luo_can_preserve(struct liveupdate_file_handler *handler,
+ struct file *file)
+{
+ return file == mshv_luo_file;
+}
+
+static const struct liveupdate_file_ops mshv_luo_file_ops = {
+ .can_preserve = mshv_luo_can_preserve,
+ .preserve = mshv_luo_preserve,
+ .unpreserve = mshv_luo_unpreserve,
+ .retrieve = mshv_luo_retrieve,
+ .freeze = mshv_luo_freeze,
+ .finish = mshv_luo_finish,
+ .owner = THIS_MODULE,
+};
+
+static struct liveupdate_file_handler mshv_luo_handler = {
+ .ops = &mshv_luo_file_ops,
+ .compatible = MSHV_LUO_FH_COMPATIBLE,
+};
+
+int __init mshv_luo_init(void)
+{
+ int err;
+
+ err = liveupdate_register_file_handler(&mshv_luo_handler);
+ if (err && err != -EOPNOTSUPP) {
+ pr_err("Could not register luo filesystem handler: %pe\n",
+ ERR_PTR(err));
+ return err;
+ }
+
+ err = liveupdate_session_create("mshv_root", &mshv_luo_file);
+ if (err)
+ goto err_session;
+
+ pr_info("mshv_root live update handler registered\n");
+ return 0;
+
+err_session:
+ liveupdate_unregister_file_handler(&mshv_luo_handler);
+ return err;
+}
+
+void __exit mshv_luo_exit(void)
+{
+ if (mshv_luo_file)
+ fput(mshv_luo_file);
+ liveupdate_unregister_file_handler(&mshv_luo_handler);
+}
diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
index c792afce0839..89d5ece0b538 100644
--- a/drivers/hv/mshv_root.h
+++ b/drivers/hv/mshv_root.h
@@ -17,6 +17,7 @@
#include <linux/build_bug.h>
#include <linux/mmu_notifier.h>
#include <uapi/linux/mshv.h>
+#include <hyperv/hvhdk.h>
/*
* Hypervisor must be between these version numbers (inclusive)
@@ -334,4 +335,16 @@ bool mshv_region_handle_gfn_fault(struct mshv_mem_region *region, u64 gfn);
void mshv_region_movable_fini(struct mshv_mem_region *region);
bool mshv_region_movable_init(struct mshv_mem_region *region);
+#if IS_ENABLED(CONFIG_LIVEUPDATE)
+int __init mshv_luo_init(void);
+void __exit mshv_luo_exit(void);
+#else
+static inline int mshv_luo_init(void)
+{
+ return 0;
+}
+
+static inline void mshv_luo_exit(void) { }
+#endif
+
#endif /* _MSHV_ROOT_H_ */
diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index 5fc572e31cd7..c0274bbc65ac 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -2330,6 +2330,10 @@ static int __init mshv_parent_partition_init(void)
if (ret)
goto deinit_root_scheduler;
+ ret = mshv_luo_init();
+ if (ret)
+ goto deinit_irqfd_wq;
+
spin_lock_init(&mshv_root.pt_ht_lock);
hash_init(mshv_root.pt_htable);
@@ -2337,6 +2341,8 @@ static int __init mshv_parent_partition_init(void)
return 0;
+deinit_irqfd_wq:
+ mshv_irqfd_wq_cleanup();
deinit_root_scheduler:
root_scheduler_deinit();
exit_partition:
@@ -2356,6 +2362,7 @@ static void __exit mshv_parent_partition_exit(void)
hv_setup_mshv_handler(NULL);
mshv_port_table_fini();
misc_deregister(&mshv_dev);
+ mshv_luo_exit();
mshv_irqfd_wq_cleanup();
root_scheduler_deinit();
if (hv_root_partition())
diff --git a/include/linux/kho/abi/mshv.h b/include/linux/kho/abi/mshv.h
new file mode 100644
index 000000000000..e6ae5a731802
--- /dev/null
+++ b/include/linux/kho/abi/mshv.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2026, Microsoft Corporation.
+ *
+ * Author: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
+ */
+
+#ifndef _LINUX_KHO_ABI_MSHV_H
+#define _LINUX_KHO_ABI_MSHV_H
+
+/* The compatibility string for mshv file handler */
+#define MSHV_LUO_FH_COMPATIBLE "mshv-v1"
+
+#endif /* _LINUX_KHO_ABI_MSHV_H */
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