linux-kernel - RE: [PATCH 8/9] KVM: x86: Add EOI exit bitmap inference

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Message-ID: <E959C4978C3B6342920538CF579893F00267F7C9@SHSMSX104.ccr.corp.intel.com>
Date:	Fri, 7 Aug 2015 22:55:10 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:	Steve Rutherford <srutherford@...gle.com>,
	"rkrcmar@...hat.com" <rkrcmar@...hat.com>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH 8/9] KVM: x86: Add EOI exit bitmap inference



> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini@...il.com] On Behalf Of Paolo
> Bonzini
> Sent: Friday, August 07, 2015 6:17 PM
> To: Wu, Feng; linux-kernel@...r.kernel.org; kvm@...r.kernel.org
> Cc: Steve Rutherford; rkrcmar@...hat.com
> Subject: Re: [PATCH 8/9] KVM: x86: Add EOI exit bitmap inference
> 
> 
> 
> On 07/08/2015 09:46, Wu, Feng wrote:
> > If I understand it correctly, here you reserve the low part of the routing
> > table, and insert entries with KVM_IRQ_ROUTING_MSI type in them,
> > then you use this as a hint to KVM to set the EOI bit map. I have two
> > concerns:
> >
> > - Currently, GSI 2 is used for MSI routing, I want to make sure after this
> > patch, whether GSI 2 can still be used for _real_ MSI routing, if it can,
> > does everything work correctly?
> 
> The patch has no effect if you use the in-kernel IOAPIC.  If you use a
> userspace IOAPIC you won't be able to use GSI 2 for MSI routing because
> it falls in the reserved range.

Good to know this, it addresses my concern, thanks!

> 
> > - Now, KVM_IRQ_ROUTING_MSI and KVM_IRQ_ROUTING_IRQCHIP
> > type entries cannot share the same map[gsi] (pls refer to the following
> > code), so where should be the IOAPIC entries exist in the map[] array?
> 
> With split irqchip, only KVM_IRQ_ROUTING_MSI is used.  Does this answer
> your question?

Ah, I got it, since the IOAPIC is in userspace, there is no need to add the IOAPIC
routing information in the routing table. Thanks for the clarification!

Thanks,
Feng

> 
> Paolo
> 
> > static int setup_routing_entry(struct kvm_irq_routing_table *rt,
> >                                struct kvm_kernel_irq_routing_entry
> *e,
> >                                const struct kvm_irq_routing_entry
> *ue)
> > {
> >
> > 		......
> >
> >         /*
> >          * Do not allow GSI to be mapped to the same irqchip more than
> once.
> >          * Allow only one to one mapping between GSI and MSI.
> >          */
> >         hlist_for_each_entry(ei, &rt->map[ue->gsi], link)
> >                 if (ei->type == KVM_IRQ_ROUTING_MSI ||
> >                     ue->type == KVM_IRQ_ROUTING_MSI ||
> >                     ue->u.irqchip.irqchip == ei->irqchip.irqchip)
> >                         return r;
> >
> > 		......
> > }
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