Its possible that idivl overflows (due to large delta stored in usdiff,
valid scenario).
Create an exception handler to catch the overflow exception (division by zero
is protected by vcpu->arch.virtual_tsc_khz check), and interpret it accordingly
(delta is larger than USEC_PER_SEC).
Fixes https://bugzilla.redhat.com/show_bug.cgi?id=969644
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
elapsed = ns - kvm->arch.last_tsc_nsec;
if (vcpu->arch.virtual_tsc_khz) {
elapsed = ns - kvm->arch.last_tsc_nsec;
if (vcpu->arch.virtual_tsc_khz) {
/* n.b - signed multiplication and division required */
usdiff = data - kvm->arch.last_tsc_write;
#ifdef CONFIG_X86_64
usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
#else
/* do_div() only does unsigned */
/* n.b - signed multiplication and division required */
usdiff = data - kvm->arch.last_tsc_write;
#ifdef CONFIG_X86_64
usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
#else
/* do_div() only does unsigned */
- asm("idivl %2; xor %%edx, %%edx"
- : "=A"(usdiff)
- : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
+ asm("1: idivl %[divisor]\n"
+ "2: xor %%edx, %%edx\n"
+ " movl $0, %[faulted]\n"
+ "3:\n"
+ ".section .fixup,\"ax\"\n"
+ "4: movl $1, %[faulted]\n"
+ " jmp 3b\n"
+ ".previous\n"
+
+ _ASM_EXTABLE(1b, 4b)
+
+ : "=A"(usdiff), [faulted] "=r" (faulted)
+ : "A"(usdiff * 1000), [divisor] "rm"(vcpu->arch.virtual_tsc_khz));
+
#endif
do_div(elapsed, 1000);
usdiff -= elapsed;
if (usdiff < 0)
usdiff = -usdiff;
#endif
do_div(elapsed, 1000);
usdiff -= elapsed;
if (usdiff < 0)
usdiff = -usdiff;
+
+ /* idivl overflow => difference is larger than USEC_PER_SEC */
+ if (faulted)
+ usdiff = USEC_PER_SEC;
} else
usdiff = USEC_PER_SEC; /* disable TSC match window below */
} else
usdiff = USEC_PER_SEC; /* disable TSC match window below */