linux-kernel - Re: [PATCH v2 1/6] kvm: Pass kvm

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Date:	Thu, 28 Jun 2012 19:56:53 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>, avi@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	jan.kiszka@...mens.com
Subject: Re: [PATCH v2 1/6] kvm: Pass kvm_irqfd to functions

On Thu, Jun 28, 2012 at 06:51:09PM +0200, Cornelia Huck wrote:
> On Thu, 28 Jun 2012 15:09:49 +0300
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
> 
> > On Thu, Jun 28, 2012 at 02:00:41PM +0200, Cornelia Huck wrote:
> > > On Thu, 28 Jun 2012 12:34:43 +0300
> > > "Michael S. Tsirkin" <mst@...hat.com> wrote:
> > > 
> > > > On Thu, Jun 28, 2012 at 11:03:16AM +0200, Cornelia Huck wrote:
> > > 
> > > > > How about something like this as parameter for the new ioctl?
> > > > > 
> > > > > struct kvm_irqfd2 {
> > > > > 	__u32 fd;
> > > > > 	__u32 flags;  /* for things like deassign */
> > > > > 	__u64 type;   /* determines the payload */
> > > > > 	union {
> > > > > 		/* type traditional */
> > > > > 		struct {
> > > > > 			__u32 gsi;
> > > > > 		} trad;
> > > > > 		/* type s390 */
> > > > > 		struct {
> > > > > 			__u32 int_type;
> > > > > 			__u32 parm;
> > > > > 			__u64 parm64;
> > > > > 		} s390;
> > > > > 		__u8 pad[20];
> > > > > 	};
> > > > > }
> > > > > 
> > > > > This could be combined with an arch or a per-kvm callback to keep the
> > > > > generic code clean of architecture dependencies.
> > > > > 
> > > > > Cornelia
> > > > 
> > > > Looks a bit weird - shouldn't all this be part of gsi routing?
> > > > But no idea really, I don't see the big picture here.
> > > > 
> > > 
> > > Well, on s390 we don't have anything like "gsi routing" (I'm not even
> > > really sure what that is).
> > 
> > I really mean kvm_irq_routing. This has options for
> > irqchip, msi, I guess we can add more.
> 
> I stared at irq_comm.c for a bit and it seems to fulfill a purpose
> similar to arch/s390/kvm/interrupt.c (although it looks more static).
> But I don't really see how they could fit together easily.
> 
> > 
> > 
> > > My understanding is the following:
> > > 
> > > - Basically, we want to notify the guest for a virtqueue.
> > > - For this, we want to inject an interrupt for the associated device.
> > > - On x86, this means raising an interrupt on an interrupt line, as
> > >   specified by some kind of number.
> > 
> > Not just that: for MSI we pass in data encoding priority
> > destination etc.
> > 
> > > - On s390, we need some more information to (a) identify the device and
> > >   (b) additional information that needs to be transmitted for an
> > >   interrupt (device specific). (This is what basically goes into struct
> > >   kvm_s390_interrupt, which I reproduced in the s390 part.)
> > > 
> > > Cornelia
> > 
> > Is this b mostly static or does it change for each interrupt?
> 
> For Linux guests it will be static, although the architecture would
> allow for changing (some of) it.
> 
> Cornelia

So storing this info in routing might be a good fit.

-- 
MST
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