[PATCH v3 01/12] math64.h: Add mul_s64_u64_shr()

Ilias Stamatis
2021-05-21T10:26:31Z

This function is needed for KVM's nested virtualization. The nested TSC
scaling implementation requires multiplying the signed TSC offset with
the unsigned TSC multiplier.

Signed-off-by: Ilias Stamatis <ilstam@amazon.com>
---
include/linux/math64.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/include/linux/math64.h b/include/linux/math64.h
index 66deb1fdc2ef..2928f03d6d46 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -3,6 +3,7 @@
#define _LINUX_MATH64_H

#include <linux/types.h>
+#include <linux/math.h>
#include <vdso/math64.h>
#include <asm/div64.h>

@@ -234,6 +235,24 @@ static inline u64 mul_u64_u64_shr(u64 a, u64 b, unsigned int shift)

#endif

+#ifndef mul_s64_u64_shr
+static inline u64 mul_s64_u64_shr(s64 a, u64 b, unsigned int shift)
+{
+ u64 ret;
+
+ /*
+ * Extract the sign before the multiplication and put it back
+ * afterwards if needed.
+ */
+ ret = mul_u64_u64_shr(abs(a), b, shift);
+
+ if (a < 0)
+ ret = -((s64) ret);
+
+ return ret;
+}
+#endif /* mul_s64_u64_shr */
+
#ifndef mul_u64_u32_div
static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 divisor)
{
--
2.17.1