Re: [PATCH v2 3/6] KVM: x86: make pic setup code look like ioapic setup

[David Hildenbrand]

Am 03.01.2017 um 17:12 schrieb Paolo Bonzini:
> On 03/01/2017 14:04, David Hildenbrand wrote:
> > Am 16.12.2016 um 16:10 schrieb Radim KrÄmÃÅ:
> > > We don't treat kvm->arch.vpic specially anymore, so the setup can look
> > > like ioapic.  This gets a bit more information out of return values.
> >
> > This originally saved us from a race condition as far as I can
> > reconstruct from the commit history. Think the problem was
> > vpic being set but routes not being set up yet.
> >
> > commit 71ba994c94a81c37185ef2fb5190844286ba9aca
> > Author: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Date:   Wed Jul 29 12:31:15 2015 +0200
> >
> >     KVM: x86: clean/fix memory barriers in irqchip_in_kernel
> >
> >     The memory barriers are trying to protect against concurrent RCU-based
> >     interrupt injection, but the IRQ routing table is not valid at the time
> >     kvm->arch.vpic is written.  Fix this by writing kvm->arch.vpic last.
> >     kvm_destroy_pic then need not set kvm->arch.vpic to NULL; modify it
> >     to take a struct kvm_pic* and reuse it if the IOAPIC creation fails.
> >
> >     Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> >
> > I assume that this is now fixed via the irqchip_mode, as it is stored
> > last? If so, I really like this patch :)
>
> Yes, the previous patch referred to that when it said
> "irqchip_in_kernel() tried to save a bit by reusing pic_irqchip()", and
> what this commit message means by "not trteating kvm->arch.vpic
> specially anymore".

Thanks for confirming!

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

> Paolo


--

David