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* x86: Question regarding the reset value of LINT0
@ 2015-04-08 16:40 Nadav Amit
  2015-04-08 16:44 ` Jan Kiszka
  0 siblings, 1 reply; 17+ messages in thread
From: Nadav Amit @ 2015-04-08 16:40 UTC (permalink / raw)
  To: kvm list

Hi,

I would appreciate if someone explains the reason for enabling LINT0 during
APIC reset. This does not correspond with Intel SDM Figure 10-8: “Local
Vector Table” that says all LVT registers are reset to 0x10000.

In kvm_lapic_reset, I see:

	apic_set_reg(apic, APIC_LVT0,
		SET_APIC_DELIVERY_MODE(0, APIC_MODE_EXTINT));

Which is actually pretty similar to QEMU’s apic_reset_common:

    if (bsp) {
        /*
         * LINT0 delivery mode on CPU #0 is set to ExtInt at initialization
         * time typically by BIOS, so PIC interrupt can be delivered to the
         * processor when local APIC is enabled.
         */
        s->lvt[APIC_LVT_LINT0] = 0x700;
    }

Yet, in both cases, I miss the point - if it is typically done by the BIOS,
why does QEMU or KVM enable it?

BTW: KVM seems to run fine without it, and I think setting it causes me
problems in certain cases.

Thanks,
Nadav

^ permalink raw reply	[flat|nested] 17+ messages in thread

end of thread, other threads:[~2015-04-13 12:02 UTC | newest]

Thread overview: 17+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-04-08 16:40 x86: Question regarding the reset value of LINT0 Nadav Amit
2015-04-08 16:44 ` Jan Kiszka
2015-04-08 16:59   ` Nadav Amit
2015-04-08 17:06     ` Jan Kiszka
2015-04-08 17:40       ` Nadav Amit
2015-04-08 17:51         ` Jan Kiszka
2015-04-08 21:49           ` Nadav Amit
2015-04-08 22:11             ` Bandan Das
2015-04-09 18:21               ` Nadav Amit
2015-04-09 18:28                 ` Avi Kivity
2015-04-09 18:49                   ` Nadav Amit
2015-04-09 19:17                     ` Bandan Das
2015-04-10  9:12                       ` Paolo Bonzini
2015-04-12 18:29                         ` Nadav Amit
2015-04-12 22:53                           ` [PATCH] KVM: x86: Support for disabling quirks Nadav Amit
2015-04-13 10:34                             ` Paolo Bonzini
2015-04-13 12:02                               ` Nadav Amit

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