[PATCH RFC: kvm tsc virtualization 16/20] Fix 32-bit mult_precise

Zachary Amsden
2009-12-15T04:08:56Z

Turns out it wasn't very precise; it needs to work on 64-bit values.

Signed-off-by: Zachary Amsden <zamsden@redhat.com>
---
arch/x86/kvm/x86.c | 18 +++++++++++++++---
1 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7e2ba3e..792c895 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -803,15 +803,27 @@ static void compute_best_multiplier(unsigned long a, unsigned long b,
*s = shift;
}

-static inline unsigned long mult_precise(unsigned long val, unsigned long mult,
- int shift)
+static inline u64 mult_precise(u64 val, unsigned long mult, int shift)
{
+#if (BITS_PER_LONG == 64)
unsigned long top, bot;

- __asm__ ( "mul %3; shrd %1, %0" :
+ __asm__ ( "mulq %3; shrdq %1, %0" :
"=&a" (bot), "=&d" (top) :
"0" (mult), "rm" (val), "c" (shift));
return bot;
+#else
+ unsigned long ltop, lbot;
+ unsigned long htop, hbot;
+
+ __asm__ ( "mull %3; shrd %1, %0" :
+ "=&a" (lbot), "=&d" (ltop) :
+ "0" (mult), "rm" (long)(val), "c" (shift));
+ __asm__ ( "mull %3; shrd %1, %0" :
+ "=&a" (hbot), "=&d" (htop) :
+ "0" (mult), "rm" (long)(val >> 32), "c" (shift));
+ return (u64)lbot + ((u64)ltop + (u64)hbot) << 32;
+#endif
}

static inline u64 compute_ref_tsc(void)
--
1.6.5.2