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

Maxim Levitsky
2021-05-24T17:49:27Z

On Fri, 2021-05-21 at 11:24 +0100, Ilias Stamatis wrote:
> 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)
> {

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky