From 0677dbd4b582d1a913462d75caad0abf21e87f32 Mon Sep 17 00:00:00 2001
From: Ciro Santilli <ciro.santilli@gmail.com>
Date: Sun, 16 Jul 2017 12:49:09 +0100
Subject: [PATCH] virt_to_phys only works for kmalloc

---
 buildroot_config_fragment      |  6 +++++-
 kernel_module/virt_to_phys.c   | 30 +++++++++++++++++++-----------
 rootfs_overlay/virt_to_phys.sh | 11 ++++++++---
 3 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/buildroot_config_fragment b/buildroot_config_fragment
index 7578b79..153164d 100644
--- a/buildroot_config_fragment
+++ b/buildroot_config_fragment
@@ -54,7 +54,11 @@ BR2_PACKAGE_HOST_DTC=y
 #
 #     xp/4 0x101e9000
 #
-# Uses /dev/mem:
+# Uses /dev/mem.
+#
+# Upstream: http://free-electrons.com/pub/mirror/devmem2.c
+#
+# See also:
 #
 # - https://superuser.com/questions/71389/what-is-dev-mem/1214662#1214662
 # - https://unix.stackexchange.com/questions/4948/shell-command-to-read-device-registers
diff --git a/kernel_module/virt_to_phys.c b/kernel_module/virt_to_phys.c
index 5433827..2cd5438 100644
--- a/kernel_module/virt_to_phys.c
+++ b/kernel_module/virt_to_phys.c
@@ -3,7 +3,7 @@ Also try on QEMU monitor:
 
 	xp 0x<vaddr>
 
-x86 docs say it only works for kmalloc.
+Only works for kmalloc.
 
 static inline phys_addr_t virt_to_phys(volatile void *address)
 
@@ -21,19 +21,26 @@ static inline phys_addr_t virt_to_phys(volatile void *address)
 #include <linux/seq_file.h> /* single_open, single_release */
 #include <linux/slab.h> /* kmalloc, kfree */
 
-static volatile u32 *i;
+static volatile u32 *k;
+static volatile u32 i;
 
 static struct dentry *debugfs_file;
 
 static int show(struct seq_file *m, void *v)
 {
 	seq_printf(m,
-		"*i 0x%llx\n"
-		"i %p\n"
-		"virt_to_phys 0x%llx\n",
-		(unsigned long long)*i,
-		i,
-		(unsigned long long)virt_to_phys((void *)i)
+		"k 0x%llx\n"
+		"addr_k %p\n"
+		"virt_to_phys_k 0x%llx\n"
+		"i 0x%llx\n"
+		"addr_i %p\n"
+		"virt_to_phys_i 0x%llx\n",
+		(unsigned long long)*k,
+		k,
+		(unsigned long long)virt_to_phys((void *)k),
+		(unsigned long long)i,
+		&i,
+		(unsigned long long)virt_to_phys((void *)&i)
 	);
 	return 0;
 }
@@ -53,8 +60,9 @@ static const struct file_operations fops = {
 
 static int myinit(void)
 {
- 	i = kmalloc(sizeof(i), GFP_KERNEL);
- 	*i = 0x12345678;
+ 	k = kmalloc(sizeof(k), GFP_KERNEL);
+ 	*k = 0x12345678;
+ 	i = 0x12345678;
 	debugfs_file = debugfs_create_file(
 		"lkmc_virt_to_phys", S_IRUSR, NULL, NULL, &fops);
 	return 0;
@@ -63,7 +71,7 @@ static int myinit(void)
 static void myexit(void)
 {
 	debugfs_remove(debugfs_file);
-	kfree((void *)i);
+	kfree((void *)k);
 }
 
 module_init(myinit)
diff --git a/rootfs_overlay/virt_to_phys.sh b/rootfs_overlay/virt_to_phys.sh
index b0ab00e..801df46 100755
--- a/rootfs_overlay/virt_to_phys.sh
+++ b/rootfs_overlay/virt_to_phys.sh
@@ -3,10 +3,15 @@ set -ex
 insmod /virt_to_phys.ko
 cd /sys/kernel/debug
 cat lkmc_virt_to_phys
-# *i = 0x12345678
-addr=$(grep virt_to_phys lkmc_virt_to_phys | cut -d ' ' -f 2)
+# k = 0x12345678
+# i = 0x12345678
+addr=$(awk '$1 == "virt_to_phys_k" { print $2 }' lkmc_virt_to_phys)
+devmem2 "$addr"
+devmem2 "$addr" w 0x9ABCDEF0
+addr=$(awk '$1 == "virt_to_phys_i" { print $2 }' lkmc_virt_to_phys)
 devmem2 "$addr"
 devmem2 "$addr" w 0x9ABCDEF0
 cat lkmc_virt_to_phys
-# *i = 0x9ABCDEF0
+# k = 0x9ABCDEF0
+# i = 0x12345678
 rmmod virt_to_phys