Il giorno venerdì 17 marzo 2017 13:43:32 UTC+1, J. Kiszka ha scritto:
> On 2017-03-17 13:06, Claudio Scordino wrote:
> > Dear all,
> >
> > we are facing an unexpected exception when running the apic timer to
> > drive a GPIO as a software PWM.
> >
> > The platform is x86. The software runs in a bare-metal cell. The PWM
> > frequency is 5 KHz.
> >
> > When the duty cycle is very high or very low (i.e., two subsequent
> > interrupts get closer) we face the following unexpected exception:
> >
> > FATAL: Unhandled VM-Exit, reason 2
> > qualification 0
> > vectoring info: 0 interrupt info: 0
> > RIP: 0x00000000000f15d6 RSP: 0x00000000000dff08 FLAGS: 10002
>
> "objdump -dS inmate-linked.o" can tell you which instruction at RIP
> causes this fault. It's a triple fault, likely started off by a general
> protection or page fault.
>
> Jan
Hi I'm Errico, Claudio's coworker, and I'm actually playing with this issue.
The fault happens when we re-arm the apic timer
00000000000f15b5 <apic_timer_set>:
void apic_timer_set(unsigned long timeout_ns)
{
unsigned long long ticks =
(unsigned long long)timeout_ns * divided_apic_freq;
write_msr(X2APIC_TMICT, ticks / NS_PER_SEC);
f15b5: 48 89 f8 mov %rdi,%rax
f15b8: b9 00 ca 9a 3b mov $0x3b9aca00,%ecx
f15bd: 31 d2 xor %edx,%edx
f15bf: 48 0f af 05 f1 10 ff imul -0xef0f(%rip),%rax #
e26b8 <divided_apic_freq>
f15c6: ff
f15c7: 48 f7 f1 div %rcx
f15ca: b9 38 08 00 00 mov $0x838,%ecx
f15cf: 48 89 c2 mov %rax,%rdx
f15d2: 48 c1 ea 20 shr $0x20,%rdx
f15d6: 0f 30 wrmsr
f15d8: c3 retq
It is the *wrmsr* inside the apic_timer_set to generate the fault.
Since I'm not expert of x86 (I'm more an embedded guy), I'm asking for tips and
ideas.
Regards,
Errico Guidieri
>
> > RAX: 0x000000044b82f9d8 RBX: 0x00000000000f060f RCX: 0x0000000000000838
> > RDX: 0x0000000000000004 RSI: 0x0000000000000a36 RDI: 0xffffffffffffe134
> > CS: 10 BASE: 0x0000000000000000 AR-BYTES: a09b EFER.LMA 1
> > CR0: 0x0000000080010031 CR3: 0x00000000000f3000 CR4: 0x0000000000002020
> > EFER: 0x0000000000000500
> > Parking CPU 3 (Cell: "pwm-demo")
> > Closing cell "pwm-demo"
> > Page pool usage after cell destruction: mem 4316/16327, remap 16459/131072
> > CPU 3 received SIPI, vector 98
> >
> >
> > Attached the code of the inmate.
> >
> > Any suggestion about the reason of this behavior ?
> >
> > Many thanks and best regards,
> >
> > Claudio
> >
> > --
> > Claudio Scordino, Ph.D.
> > Project Manager - Funded research projects
> >
> > Evidence Srl
> > Via Carducci 56
> > 56010 S.Giuliano Terme - Pisa - Italy
> > Phone: +39 050 99 11 224
> > Mobile: + 39 393 811 7491
> > Fax: +39 050 99 10 812
> > http://www.evidence.eu.com <http://www.evidence.eu.com/>
> >
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