Re: [KVM PATCH v7 2/2] KVM: add iosignalfd support

[Avi Kivity]

On 06/18/2009 05:09 PM, Gregory Haskins wrote:
> Avi Kivity wrote:
>    
> > On 06/18/2009 03:09 PM, Gregory Haskins wrote:
> >      
> > > > > +config KVM_MAX_IOSIGNALFD_ITEMS
> > > > > +    int "Maximum IOSIGNALFD items per address"
> > > > > +    depends on KVM
> > > > > +    default "32"
> > > > > +    ---help---
> > > > > +      This option influences the maximum number of fd's per PIO/MMIO
> > > > > +      address that are allowed to register
> > > > > +
> > > > >
> > > > >
> > > > >            
> > > > Is there a per-vm limit on iosignalfds?  if not, userspace can exhaust
> > > > kernel memory in that way.
> > > >
> > > >          
> > > Yeah, its already naturally limited by the maximum number of MMIO/PIO
> > > devices we can register (today this is 6 per VM).  I should have
> > > documented that fact somewhere, tho.
> > >
> > >        
> > We need to raise this limit drastically and to expose it.
> >      
>
> Any suggestions on a target #?  512?
>    

Let's say 20 devices with 16 queues each.  That gives 320 fds.  So 512 
seems like a good choice for now.

But don't make it Kconfigurable, there's no way the user will know what 
to put there.
> > No, a u16 will naturally expand to a u64, and the emulator will
> > generate the correct value.
> >      
>
> Right, I understand that part.  What I mean specifically is at run-time
> when the IO comes in.  I was thinking I would need to do a memcmp
> against the u64 and the data-register and it was hurting my head trying
> to figure out what pointer to pass to memcmp.
>
> <lightbulb turns on>
>
> Duh, I can just load the data-register into a u64 and check equality.
> Nevermind, I am a dumbass ;)
>    

I see on your v8 what the load means.  It's not so pretty.  But we can 
have generic code do the load and pass a u64 instead of a pointer.

But please, only after this goes in.

--
error compiling committee.c: too many arguments to function

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