Re: [Qemu-devel] [PATCH v3 12/13] q35: ioapic: add support for split irqchip and irqfd

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, Apr 16, 2016 at 07:44:12PM -0700, Jan Kiszka wrote:
> On 2016-04-14 20:31, Peter Xu wrote:
> > This patch allows Intel IR work with splitted irqchip. Two more fields
> > are added to IOAPICCommonState to support the translation process (For
> > future AMD IR support, we will need to provide another AMD-specific
> > callback for int_remap()). In split irqchip mode, IOAPIC is working in
> > user space, only update kernel irq routes when entry changed. When IR is
> > enabled, we directly update the kernel with translated messages. It
> > works just like a kernel cache for the remapping entries.
> > 
> > Since KVM irqfd is using kernel gsi routes to deliver interrupts, as
> > long as we can support split irqchip, we will support irqfd as
> > well. Also, since kernel gsi routes will cache translated interrupts,
> > irqfd delivery will not suffer from any performance impact due to IR.
> > 
> > And, since we supported irqfd, vhost devices will be able to work
> > seamlessly with IR now. Logically this should contain both vhost-net and
> > vhost-user case.
> > 
> > Here we avoided capturing IOMMU IR invalidation, based on the assumption
> > that, guest kernel will always first update IR entry, then IOAPIC
> > entry. As long as guest follows this order to update IOAPIC entries, we
> > should be safe.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  hw/i386/intel_iommu.c             |  9 +++++++--
> >  hw/intc/ioapic.c                  | 39 ++++++++++++++-------------------------
> >  hw/intc/ioapic_common.c           |  4 ++++
> >  include/hw/i386/intel_iommu.h     |  2 ++
> >  include/hw/i386/ioapic_internal.h |  5 +++++
> >  5 files changed, 32 insertions(+), 27 deletions(-)
> > 
> > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> > index 68ebc1e..104afeb 100644
> > --- a/hw/i386/intel_iommu.c
> > +++ b/hw/i386/intel_iommu.c
> > @@ -2077,9 +2077,9 @@ static int vtd_interrupt_remap_msi(IntelIOMMUState *iommu,
> >      uint16_t index = 0;
> >      VTDIrq irq = {0};
> >  
> > -    assert(iommu && origin && translated);
> > +    assert(origin && translated);
> >  
> > -    if (!iommu->intr_enabled) {
> > +    if (!iommu || !iommu->intr_enabled) {
> >          memcpy(translated, origin, sizeof(*origin));
> >          return 0;
> >      }
> > @@ -2143,6 +2143,11 @@ static int vtd_interrupt_remap_msi(IntelIOMMUState *iommu,
> >      return 0;
> >  }
> >  
> > +int vtd_int_remap(void *iommu, MSIMessage *src, MSIMessage *dst)
> > +{
> > +    return vtd_interrupt_remap_msi(iommu, src, dst);
> > +}
> > +
> >  static uint64_t vtd_mem_ir_read(void *opaque, hwaddr addr, unsigned size)
> >  {
> >      uint64_t data = 0;
> > diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
> > index 84e8948..b993bd0 100644
> > --- a/hw/intc/ioapic.c
> > +++ b/hw/intc/ioapic.c
> > @@ -182,34 +182,23 @@ static void ioapic_update_kvm_routes(IOAPICCommonState *s)
> >  {
> >  #ifdef CONFIG_KVM
> >      int i;
> > +    int ret;
> >  
> >      if (kvm_irqchip_is_split()) {
> >          for (i = 0; i < IOAPIC_NUM_PINS; i++) {
> > -            uint64_t entry = s->ioredtbl[i];
> > -            uint8_t trig_mode;
> > -            uint8_t delivery_mode;
> > -            uint8_t dest;
> > -            uint8_t dest_mode;
> > -            uint64_t pin_polarity;
> > -            MSIMessage msg;
> > -
> > -            trig_mode = ((entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) & 1);
> > -            dest = entry >> IOAPIC_LVT_DEST_SHIFT;
> > -            dest_mode = (entry >> IOAPIC_LVT_DEST_MODE_SHIFT) & 1;
> > -            pin_polarity = (entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) & 1;
> > -            delivery_mode =
> > -                (entry >> IOAPIC_LVT_DELIV_MODE_SHIFT) & IOAPIC_DM_MASK;
> > -
> > -            msg.address = APIC_DEFAULT_ADDRESS;
> > -            msg.address |= dest_mode << 2;
> > -            msg.address |= dest << 12;
> > -
> > -            msg.data = entry & IOAPIC_VECTOR_MASK;
> > -            msg.data |= delivery_mode << APIC_DELIVERY_MODE_SHIFT;
> > -            msg.data |= pin_polarity << APIC_POLARITY_SHIFT;
> > -            msg.data |= trig_mode << APIC_TRIG_MODE_SHIFT;
> > -
> > -            kvm_irqchip_update_msi_route(kvm_state, i, msg, NULL);
> > +            MSIMessage src, dst;
> > +            struct ioapic_entry_info info;
> > +            ioapic_entry_parse(s->ioredtbl[i], &info);
> > +            src.address = info.addr;
> > +            src.data = info.data;
> > +            /* We update kernel irqchip routes with translated
> > +             * results. */
> > +            ret = s->int_remap(s->iommu, &src, &dst);
> > +            if (ret) {
> > +                DPRINTF("Int remap failed: %d, drop interrupt\n", ret);
> > +                continue;
> > +            }
> > +            kvm_irqchip_update_msi_route(kvm_state, i, dst, NULL);
> 
> The need to hook here makes me wonder if we can't inject IOAPIC
> interrupts via KVM_SIGNAL_MSI (abstracted by kvm_irqchip_send_msi, but
> that will pick the fast-path on kernels supporting split irqchip)
> instead of open-coding the route changes. If we translated the IOAPIC
> outputs always into MSIs, the need for special-casing split irqchip
> would be gone, and the need for hooking here for IR just as well.
> 
> Jan

Will work for irqfd as well.

-- 
MST