Re: [Qemu-devel] [PATCH 12/13] spapr/xics: ignore the lower 4K in the IRQ number space

[David Gibson]

On Tue, Feb 12, 2019 at 08:05:53AM +0100, Cédric Le Goater wrote:
> On 2/12/19 2:06 AM, David Gibson wrote:
> > On Mon, Jan 07, 2019 at 07:39:45PM +0100, Cédric Le Goater wrote:
> >> The IRQ number space of the XIVE and XICS interrupt mode are aligned
> >> when using the dual interrupt mode for the machine. This means that
> >> the ICS offset is set to zero in QEMU and that the KVM XICS device
> >> should be informed of this new value. Unfortunately, there is now way
> >> to do so and KVM still maintains the XICS_IRQ_BASE (0x1000) offset.
> >>
> >> Ignore the lower 4K which are not used under the XICS interrupt
> >> mode. These IRQ numbers are only claimed by XIVE for the CPU IPIs.
> >>
> >> Signed-off-by: Cédric Le Goater <address@hidden>
> >> ---
> >>  hw/intc/xics_kvm.c | 18 ++++++++++++++++++
> >>  1 file changed, 18 insertions(+)
> >>
> >> diff --git a/hw/intc/xics_kvm.c b/hw/intc/xics_kvm.c
> >> index 651bbfdf6966..1d21ff217b82 100644
> >> --- a/hw/intc/xics_kvm.c
> >> +++ b/hw/intc/xics_kvm.c
> >> @@ -238,6 +238,15 @@ static void ics_get_kvm_state(ICSState *ics)
> >>      for (i = 0; i < ics->nr_irqs; i++) {
> >>          ICSIRQState *irq = &ics->irqs[i];
> >>  
> >> +        /*
> >> +         * The KVM XICS device considers that the IRQ numbers should
> >> +         * start at XICS_IRQ_BASE (0x1000). Ignore the lower 4K
> >> +         * numbers (only claimed by XIVE for the CPU IPIs).
> >> +         */
> >> +        if (i + ics->offset < XICS_IRQ_BASE) {
> >> +            continue;
> >> +        }
> >> +
> > 
> > This seems bogus to me.  The guest-visible irq numbers need to line up
> > between xics and xive mode, yes, but that doesn't mean we need to keep
> > around a great big array of unused array of ICS irq states, even in
> > TCG mode.
> 
> This is because the qirqs[] array is under the machine and shared between 
> both interrupt modes, xics and xive.

I don't see how that follows.  ICSIRQState is indexed in terms of the
ICS source number, not the global irq number, so I don't see why it
has to match up with the qirq array.

> 
> C.
> 
> > 
> >>          kvm_device_access(kernel_xics_fd, KVM_DEV_XICS_GRP_SOURCES,
> >>                            i + ics->offset, &state, false, &error_fatal);
> >>  
> >> @@ -303,6 +312,15 @@ static int ics_set_kvm_state(ICSState *ics, int 
> >> version_id)
> >>          ICSIRQState *irq = &ics->irqs[i];
> >>          int ret;
> >>  
> >> +        /*
> >> +         * The KVM XICS device considers that the IRQ numbers should
> >> +         * start at XICS_IRQ_BASE (0x1000). Ignore the lower 4K
> >> +         * numbers (only claimed by XIVE for the CPU IPIs).
> >> +         */
> >> +        if (i + ics->offset < XICS_IRQ_BASE) {
> >> +            continue;
> >> +        }
> >> +
> >>          state = irq->server;
> >>          state |= (uint64_t)(irq->saved_priority & KVM_XICS_PRIORITY_MASK)
> >>              << KVM_XICS_PRIORITY_SHIFT;
> > 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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