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Re: [Xen-devel] INIT ipi under Xen

To: Rafal Wojtczuk <rafal@xxxxxxxxxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] INIT ipi under Xen
From: Keir Fraser <keir@xxxxxxx>
Date: Fri, 14 Jan 2011 15:44:19 +0000
Delivery-date: Fri, 14 Jan 2011 07:45:14 -0800
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Thread-topic: [Xen-devel] INIT ipi under Xen
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On 14/01/2011 14:54, "Rafal Wojtczuk" <rafal@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hello,
>     Does anyone know whether Xen-4.0.1, after it has booted and created dom0,
> does 
> anything special to prevent interprocessor interrupt with delivery mode INIT
> from 
> affecting processors ? Judging by Intel Software Developer Manual there is no
> documented way to do this; but maybe something less official ?

Intel SDM Vol.3B, 19.8 ("Restrictions on VMX Operation"), final bullet
point: "The INIT signal is blocked whenever a logical processor is in VMX
root operation."

Also, your code won't work if the APIC happens to be in x2APIC mode. You
should write to the ICR with apic_icr_write(), which handles both xAPIC and
x2APIC modes correctly.

 -- Keir

>     I use the following piece of code (in hypervisor context) to trigger IPI:
> unsigned long send_init_ipi()
> {
>         unsigned long ret;
>         int i;
>         rdmsrl(IA32_APIC_BASE, ret);
>         xen_printk("IA32_APIC_BASE=0x%x\n", ret);
>         if (ret & (1 << 8)) {   // I am BSP
>                 *(unsigned int *) (APIC_BASE + 0x300) = 0xc4500; // load ICR1
>                 asm("wbinvd"); // just in case APIC_BASE is cached WB
>         }
>         return ret;
> }
> This code does not seem to cause any effect (even when
> IA32_APIC_BASE=0xfee00900 is logged) - namely, I can still observe both CPUs
> running: subsequent triggering of this code sometimes results in
> IA32_APIC_BASE=0xfee00900 logged, sometimes 0xfee00800.
> If I try sending "ordinary" interrupts (by
> eg writing 0x4169 do ICR1) I can see the interrupt count in /proc/cpuinfo
> increase. Moreover, if I run the above code when a HVM is running, then it
> is killed with note in the Xen log that unexpected exit_reason=3 (meaning,
> EXIT_REASON_INIT) has beed observed. So, everything indicates that indeed
> the above code generates INIT, but somehow it is ignored by the destination.
> Even writing 0x84500 (send INIT to every CPU) causes no effect.
> The similar code run on bare metal Linux behaves more sanely.
> Can anyone offer a clue ? This is on Intel Q45 board, E8400 CPU, 64bit
> Xen-4.0.1.
> RW
> PS
> Similarly, sending SIPI causes nothing; but I would expect that SIPI is
> reacted upon only in wait-for-SIPI state. However, this is not documented
> anywhere - can someone confirm this assumption more authoritatively ?
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