Re: [PATCH v5 3/4] KVM: x86: Add EOI exit bitmap inference

[Steve Rutherford <srutherford@google.com>]

On Thu, Jul 30, 2015 at 08:23:43AM +0200, Jan Kiszka wrote:
> On 2015-07-29 22:27, Steve Rutherford wrote:
> > On Wed, Jul 29, 2015 at 02:38:09PM +0200, Paolo Bonzini wrote:
> >>
> >>
> >> On 28/07/2015 01:17, Steve Rutherford wrote:
> >>> diff --git a/arch/x86/kvm/ioapic.h b/arch/x86/kvm/ioapic.h
> >>> index d8cc54b..f6ce112 100644
> >>> --- a/arch/x86/kvm/ioapic.h
> >>> +++ b/arch/x86/kvm/ioapic.h
> >>> @@ -9,6 +9,7 @@ struct kvm;
> >>>  struct kvm_vcpu;
> >>>  
> >>>  #define IOAPIC_NUM_PINS  KVM_IOAPIC_NUM_PINS
> >>> +#define MAX_NR_RESERVED_IOAPIC_PINS 48
> >>
> >> Why is this needed?
> > This constant is used to bound the number of IOAPIC pins that are
> > reservable when enabling KVM_CAP_SPLIT_IRQCHIP. IIRC, x86 doesn't
> > support more than 2 IOAPICs.  
> 
> Huh? Surely not. I've already seen boxes with at least three, and I
> think you can even hot-plug them today via extension cards. Not saying
> that QEMU supports that already, even without KVM, but we must not limit
> ourselves in the kernel API.
> 
> So please remove such a static limit on how many IOAPICs userspace can
> emulate or raise it to something sufficiently large that will last long
> enough.
I'll go with the latter. I'll set it to the same size as the max size of the
GSI routing table, which needs to upper bound it.

> 
> Jan
> 
> -- 
> Siemens AG, Corporate Technology, CT RTC ITP SES-DE
> Corporate Competence Center Embedded Linux