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

[Jan Kiszka <jan.kiszka@web.de>]

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