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@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/b164d2c1b8ff2dd764dcf064e2624dd4aa78c112
>
> 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