math64.h: Add mul_s64_u64_shr()

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>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210526184418.28881-2-ilstam@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/linux/math64.h b/include/linux/math64.h
index 66deb1fdc2ef641d1c4a917c212585be80d94751..2928f03d6d46a124b177bd299eced044a7789b11 100644 (file)
--- 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)
 {