[SeaBIOS] seabios hangs when injecting an MSI-X interrupt in early booting.

[Zhe Liu]

Dear Kevin,
    Thanks for getting back to me. Your replay helps me a lot. And there
are two things I want to make clear.
    1. > The real-mode handlers installed at 0x60-0x66 are intended for
software interrupts.
During the booting of the vm seabios, which modules will raise the software
interrupts? (Qemu? KVM? VirtualMachine?)
    2. In src/post.c: init_ivt, the handlers for 0x60-0x66 is set to none
as below.
    for (i=0x60; i<=0x66; i++)
        SET_IVT(i, SEGOFF(0, 0));
    If I change the handlers of 0x60-0x66 to default handler, which is
"iret" directly, is there some side effects?

2018-03-27 0:33 GMT+08:00 Kevin O'Connor <kevin at koconnor.net>:

> On Thu, Mar 22, 2018 at 11:40:46AM +0800, Zhe Liu wrote:
> > Hi!
> > Recently, I encountered a seabios hanging problem. When I try to inject
> an
> > MSI-X interrupt along with SMI in qemu like below:
> > *************** patch below*********************
> > diff --git a/target-i386/kvm.c b/target-i386/kvm.c- a/target-i386/kvm.c
> >
> >
> > ---   a/target-i386/kvm.c
> > +++   b/target-i386/kvm.c
> >
> > @@ -104,6 +104,7 @@ static uint32_t num_architectural_pmu_counters;
> >  static int has_xsave;
> >  static int has_xcrs;
> >  static int has_pit_state2;
> > +static int msi_count;
> >
> > static bool has_msr_mcg_ext_ctl;
> >
> > @@ -2870,12 +2871, 26 @@ void kvm_arch_pre_run(CPUState *cpu, struct
> > kvm_run *run)
> > DPRINTF("inject SMI\n");
> > + MSIMessage msg = {.address = 0x0, .data = 0x4062};
> > + if (msi_count == 1) {
> > + ret = kvm_irqchip_send_msi(kvm_state, msg);
> > + if (ret <0) {
> > + QEMU_LOG(LOG_ALERT, "MSI lost %s\n", strerror(-ret));
> > + }
> > + }
> > + msi_count++;
> >
> > ret = kvm_vcpu_ioctl(cpu, KVM_SMI);
> > if (ret < 0)
> > **************patch above*************************
> >
> > Then, when the vm will hang when booting.
> > There will be only one line in the vnc displayer:
> > "Guest has not initialized the display(yet)"
> >
> > I went through the codes(kvm qemu seabios), and I found the check_irqs
> > function in seabios will allow interrupt for a while.
> > When the interrupt triggered, the vcpu will lookup the seabios IDT table
> > and jump to the interrupt handler.
> >
> > However, in ivt_init(void), the entries from 0x60 to 0x66 will be
> cleared,
> > which is configured by the patch below.
> >
> > https://github.com/coreboot/seabios/commit/b164d2c1b8ff2dd76
> 4dcf064e2624dd4aa78c112
> >
> > So the vcpu will jump to an undefined entry instead of the default entry.
> >
> > ============================================================
> =============
> > I removed the patch, and the bug seems to disappear. I wonder if this is
> an
> > approprite solution.
>
> This doesn't seem like a SeaBIOS issue.  The real-mode handlers
> installed at 0x60-0x66 are intended for software interrupts; not for
> hardware raised interrupts.
>
> I don't know why the machine irq routing would deliver a hardware
> interrupt to that vector, but I suspect that is what needs to be
> looked at.
>
> -Kevin
>
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