This is similar to the existing div_frac function, but it returns the
remainder too. Unlike div_frac, it can be used to implement long
division, e.g. (a << 64) / b for 32-bit a and b.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 10 ++--------
arch/x86/kvm/x86.h | 15 +++++++++++++++
2 files changed, 17 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4244c2baf57d..5b937fdebc66 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1196,14 +1196,8 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
static uint32_t div_frac(uint32_t dividend, uint32_t divisor)
{
- uint32_t quotient, remainder;
-
- /* Don't try to replace with do_div(), this one calculates
- * "(dividend << 32) / divisor" */
- __asm__ ( "divl %4"
- : "=a" (quotient), "=d" (remainder)
- : "0" (0), "1" (dividend), "r" (divisor) );
- return quotient;
+ do_shl32_div32(dividend, divisor);
+ return dividend;
}
static void kvm_get_time_scale(uint32_t scaled_khz, uint32_t base_khz,
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index f2afa5fe48a6..34f416427143 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -192,4 +192,19 @@ extern unsigned int min_timer_period_us;
extern unsigned int lapic_timer_advance_ns;
extern struct static_key kvm_no_apic_vcpu;
+
+/* Same "calling convention" as do_div:
+ * - divide (n << 32) by base
+ * - put result in n
+ * - return remainder
+ */
+#define do_shl32_div32(n, base) \
+ ({ \
+ u32 __quot, __rem; \
+ asm("divl %2" : "=a" (__quot), "=d" (__rem) \
+ : "rm" (base), "0" (0), "1" ((u32) n)); \
+ n = __quot; \
+ __rem; \
+ })
+
#endif
--
1.8.3.1
--
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