From: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
---
backport/backport-include/linux/math64.h | 11 ++++++
backport/compat/Makefile | 1 +
backport/compat/backport-5.9.c | 45 ++++++++++++++++++++++++
3 files changed, 57 insertions(+)
create mode 100644 backport/backport-include/linux/math64.h
create mode 100644 backport/compat/backport-5.9.c
diff --git a/backport/backport-include/linux/math64.h b/backport/backport-include/linux/math64.h
new file mode 100644
index 000000000000..6aea9c9eec77
--- /dev/null
+++ b/backport/backport-include/linux/math64.h
@@ -0,0 +1,11 @@
+#ifndef __BACKPORT_LINUX_MATH64_H
+#define __BACKPORT_LINUX_MATH64_H
+#include_next <linux/math64.h>
+#include <linux/version.h>
+
+#if LINUX_VERSION_IS_LESS(5,9,0)
+#define mul_u64_u64_div_u64 LINUX_BACKPORT(mul_u64_u64_div_u64)
+extern u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c);
+#endif /* < 5.9 */
+
+#endif /* __BACKPORT_LINUX_MATH64_H */
diff --git a/backport/compat/Makefile b/backport/compat/Makefile
index 1d47bd59fe90..3c8430bc4958 100644
--- a/backport/compat/Makefile
+++ b/backport/compat/Makefile
@@ -11,6 +11,7 @@ compat-$(CPTCFG_KERNEL_4_18) += backport-4.18.o
compat-$(CPTCFG_KERNEL_5_2) += backport-5.2.o backport-genetlink.o
compat-$(CPTCFG_KERNEL_5_3) += backport-5.3.o
compat-$(CPTCFG_KERNEL_5_5) += backport-5.5.o
+compat-$(CPTCFG_KERNEL_5_9) += backport-5.9.o
compat-$(CPTCFG_KERNEL_5_10) += backport-5.10.o
compat-$(CPTCFG_KERNEL_5_11) += backport-5.11.o
compat-$(CPTCFG_KERNEL_5_13) += backport-5.13.o
diff --git a/backport/compat/backport-5.9.c b/backport/compat/backport-5.9.c
new file mode 100644
index 000000000000..54d1802efd31
--- /dev/null
+++ b/backport/compat/backport-5.9.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/math64.h>
+
+u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c)
+{
+ u64 res = 0, div, rem;
+ int shift;
+
+ /* can a * b overflow ? */
+ if (ilog2(a) + ilog2(b) > 62) {
+ /*
+ * (b * a) / c is equal to
+ *
+ * (b / c) * a +
+ * (b % c) * a / c
+ *
+ * if nothing overflows. Can the 1st multiplication
+ * overflow? Yes, but we do not care: this can only
+ * happen if the end result can't fit in u64 anyway.
+ *
+ * So the code below does
+ *
+ * res = (b / c) * a;
+ * b = b % c;
+ */
+ div = div64_u64_rem(b, c, &rem);
+ res = div * a;
+ b = rem;
+
+ shift = ilog2(a) + ilog2(b) - 62;
+ if (shift > 0) {
+ /* drop precision */
+ b >>= shift;
+ c >>= shift;
+ if (!c)
+ return res;
+ }
+ }
+
+ return res + div64_u64(a * b, c);
+}
+EXPORT_SYMBOL_GPL(mul_u64_u64_div_u64);
--
2.45.1
