[PATCH v1 1/8] kho: expose physical address of outgoing FDT

[Pasha Tatashin]

Expose the physical address of the outgoing KHO FDT via
/sys/kernel/debug/kho/out/fdt_phys (analogous to bootmem_phys) so
that userspace tooling can locate the root KHO FDT in physical memory.

Also add kho_debugfs_cleanup() and remove the KHO debugfs directory
if kho_init() fails after initializing debugfs, ensuring fdt_phys
does not retain a dangling pointer to a freed FDT.

This is going to be used by the upcoming KHO read-only mode.

Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
---
 Documentation/admin-guide/mm/kho.rst        |  3 +++
 kernel/liveupdate/kexec_handover.c          | 10 ++++++----
 kernel/liveupdate/kexec_handover_debugfs.c  | 22 ++++++++++++++++++++-
 kernel/liveupdate/kexec_handover_internal.h |  7 +++++--
 4 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/mm/kho.rst b/Documentation/admin-guide/mm/kho.rst
index 902d171a780a..2ba884c620c5 100644
--- a/Documentation/admin-guide/mm/kho.rst
+++ b/Documentation/admin-guide/mm/kho.rst
@@ -96,6 +96,9 @@ stabilized.
     current KHO state in this file. Kexec user space tooling can use this
     as input file for the KHO payload image.
 
+``/sys/kernel/debug/kho/out/fdt_phys``
+    Physical address of the outgoing KHO FDT blob.
+
 ``/sys/kernel/debug/kho/out/bootmem_len``
     Lengths of KHO bootmem regions, which are physically contiguous
     memory regions that will always stay available for future kexec
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 6f1f55fe3181..ce5983abf181 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -1851,17 +1851,17 @@ static __init int kho_init(void)
 	if (err)
 		goto err_free_fdt;
 
-	err = kho_out_debugfs_init(&kho_out.dbg);
+	err = kho_out_debugfs_init(&kho_out.dbg, kho_out.fdt);
 	if (err)
-		goto err_free_fdt;
+		goto err_cleanup_debugfs;
 
 	err = kho_out_fdt_setup();
 	if (err)
-		goto err_free_fdt;
+		goto err_cleanup_debugfs;
 
 	err = kho_kexec_metadata_init(fdt);
 	if (err)
-		goto err_free_fdt;
+		goto err_cleanup_debugfs;
 
 	if (fdt) {
 		kho_in_debugfs_init(&kho_in.dbg, fdt);
@@ -1893,6 +1893,8 @@ static __init int kho_init(void)
 
 	return 0;
 
+err_cleanup_debugfs:
+	kho_debugfs_cleanup();
 err_free_fdt:
 	kho_unpreserve_free(kho_out.fdt);
 err_free_kho_radix_tree:
diff --git a/kernel/liveupdate/kexec_handover_debugfs.c b/kernel/liveupdate/kexec_handover_debugfs.c
index 7d74477da0b7..db3830829398 100644
--- a/kernel/liveupdate/kexec_handover_debugfs.c
+++ b/kernel/liveupdate/kexec_handover_debugfs.c
@@ -95,6 +95,15 @@ static int bootmem_len_show(struct seq_file *m, void *v)
 }
 DEFINE_SHOW_ATTRIBUTE(bootmem_len);
 
+static int fdt_phys_show(struct seq_file *m, void *v)
+{
+	void *fdt = m->private;
+
+	seq_printf(m, "0x%llx\n", (unsigned long long)virt_to_phys(fdt));
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(fdt_phys);
+
 __init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
 {
 	struct dentry *dir, *sub_fdt_dir;
@@ -172,7 +181,7 @@ __init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
 	}
 }
 
-__init int kho_out_debugfs_init(struct kho_debugfs *dbg)
+__init int kho_out_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
 {
 	struct dentry *dir, *f, *sub_fdt_dir;
 
@@ -196,6 +205,11 @@ __init int kho_out_debugfs_init(struct kho_debugfs *dbg)
 	if (IS_ERR(f))
 		goto err_rmdir;
 
+	f = debugfs_create_file("fdt_phys", 0400, dir, (void *)fdt,
+				&fdt_phys_fops);
+	if (IS_ERR(f))
+		goto err_rmdir;
+
 	dbg->dir = dir;
 	dbg->sub_fdt_dir = sub_fdt_dir;
 	return 0;
@@ -212,3 +226,9 @@ __init int kho_debugfs_init(void)
 		return -ENOENT;
 	return 0;
 }
+
+__init void kho_debugfs_cleanup(void)
+{
+	debugfs_remove_recursive(debugfs_root);
+	debugfs_root = NULL;
+}
diff --git a/kernel/liveupdate/kexec_handover_internal.h b/kernel/liveupdate/kexec_handover_internal.h
index e9685e1ef6d7..38181076f603 100644
--- a/kernel/liveupdate/kexec_handover_internal.h
+++ b/kernel/liveupdate/kexec_handover_internal.h
@@ -24,16 +24,19 @@ extern unsigned int kho_bootmem_cnt;
 
 #ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS
 int kho_debugfs_init(void);
+void kho_debugfs_cleanup(void);
 void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt);
-int kho_out_debugfs_init(struct kho_debugfs *dbg);
+int kho_out_debugfs_init(struct kho_debugfs *dbg, const void *fdt);
 int kho_debugfs_blob_add(struct kho_debugfs *dbg, const char *name,
 			 const void *blob, size_t size, bool root);
 void kho_debugfs_blob_remove(struct kho_debugfs *dbg, void *blob);
 #else
 static inline int kho_debugfs_init(void) { return 0; }
+static inline void kho_debugfs_cleanup(void) { }
 static inline void kho_in_debugfs_init(struct kho_debugfs *dbg,
 				       const void *fdt) { }
-static inline int kho_out_debugfs_init(struct kho_debugfs *dbg) { return 0; }
+static inline int kho_out_debugfs_init(struct kho_debugfs *dbg,
+				       const void *fdt) { return 0; }
 static inline int kho_debugfs_blob_add(struct kho_debugfs *dbg,
 				       const char *name, const void *blob,
 				       size_t size, bool root) { return 0; }
-- 
2.56.0.176.g3575e65682-goog