On Mon, Jun 21, 2010 at 11:29:40AM -0400, Chris Lalancette wrote:
> 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@xxxxxxxxxx>
> ---
> arch/x86/kvm/i8259.c | 17 +++++++++++++----
> 1 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
> index 2c73f44..85ecabc 100644
> --- a/arch/x86/kvm/i8259.c
> +++ b/arch/x86/kvm/i8259.c
> @@ -44,16 +44,25 @@ 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;
> + }
> + }
Shouldn't we kick all vcpus that are in virtual write mode, not just
first one found?
> +
> + if (!found)
> + found = s->kvm->bsp_vcpu;
> +
> + kvm_vcpu_kick(found);
> }
> }
>
> --
> 1.6.6.1
>
> --
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--
Gleb.
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