Commit 529df65e authored Jun 21, 2010 by Chris Lalancette Committed by Avi Kivity Aug 01, 2010

KVM: Search the LAPIC's for one that will accept a PIC interrupt



Older versions of 32-bit linux have a "Checking 'hlt' instruction"
test where they repeatedly call the 'hlt' instruction, and then
expect a timer interrupt to kick the CPU out of halt.  This happens
before any LAPIC or IOAPIC setup happens, which means that all of
the APIC's are in virtual wire mode at this point.  Unfortunately,
the current implementation of virtual wire mode is hardcoded to
only kick the BSP, so if a crash+kexec occurs on a different
vcpu, it will never get kicked.

This patch makes pic_unlock() do the equivalent of
kvm_irq_delivery_to_apic() for the IOAPIC code.  That is, it runs
through all of the vcpus looking for one that is in virtual wire
mode.  In the normal case where LAPICs and IOAPICs are configured,
this won't be used at all.  In the bootstrap phase of a modern
OS, before the LAPICs and IOAPICs are configured, this will have
exactly the same behavior as today; VCPU0 is always looked at
first, so it will always get out of the loop after the first
iteration.  This will only go through the loop more than once
during a kexec/kdump, in which case it will only do it a few times
until the kexec'ed kernel programs the LAPIC and IOAPIC.

Signed-off-by: Chris Lalancette <clalance@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

parent 979586e0

arch/x86/kvm/i8259.c

+13 −4

Original line number	Diff line number	Diff line
		@@ -46,16 +46,25 @@ static void pic_unlock(struct kvm_pic *s)
		__releases(&s->lock)
		{
		bool wakeup = s->wakeup_needed;
		struct kvm_vcpu *vcpu;
		struct kvm_vcpu vcpu, found = NULL;
		int i;

		s->wakeup_needed = false;

		raw_spin_unlock(&s->lock);

		if (wakeup) {
		vcpu = s->kvm->bsp_vcpu;
		if (vcpu)
		kvm_vcpu_kick(vcpu);
		kvm_for_each_vcpu(i, vcpu, s->kvm) {
		if (kvm_apic_accept_pic_intr(vcpu)) {
		found = vcpu;
		break;
		}
		}

		if (!found)
		found = s->kvm->bsp_vcpu;

		kvm_vcpu_kick(found);
		}
		}

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