Re: [Qemu-devel] [PULL 29/44] spapr/xive: introduce a VM state change handler

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 29/05/2019 16:50, David Gibson wrote:
> From: Cédric Le Goater <clg@kaod.org>
> 
> This handler is in charge of stabilizing the flow of event notifications
> in the XIVE controller before migrating a guest. This is a requirement
> before transferring the guest EQ pages to a destination.
> 
> When the VM is stopped, the handler sets the source PQs to PENDING to
> stop the flow of events and to possibly catch a triggered interrupt
> occuring while the VM is stopped. Their previous state is saved. The
> XIVE controller is then synced through KVM to flush any in-flight
> event notification and to stabilize the EQs. At this stage, the EQ
> pages are marked dirty to make sure the EQ pages are transferred if a
> migration sequence is in progress.
> 
> The previous configuration of the sources is restored when the VM
> resumes, after a migration or a stop. If an interrupt was queued while
> the VM was stopped, the handler simply generates the missing trigger.
> 
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> Message-Id: <20190513084245.25755-6-clg@kaod.org>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

This one breaks my nvlink2 passthru setup. The host is v5.2-rc2.
v5.2-rc3 fixes it though so it is backward compatibility issue which we
care about to what degree here? I am forcing ic-mode=xive which is not
the default so I am not so sure.



aik@u1804kvm:~$ cat /proc/interrupts
           CPU0
 16:          0  XIVE-IPI   0 Edge      IPI
 21:          0  XIVE-IRQ 4096 Edge      RAS_EPOW
 22:          0  XIVE-IRQ 4097 Edge      RAS_HOTPLUG
257:      12372  XIVE-IRQ 4353 Edge      ibmvscsi
258:          0  XIVE-IRQ 4864 Edge      virtio0-config
259:       2157  XIVE-IRQ 4865 Edge      virtio0-input.0
260:          1  XIVE-IRQ 4866 Edge      virtio0-output.0
261:          0  XIVE-IRQ 4868 Edge      xhci_hcd
262:          0  XIVE-IRQ 4869 Edge      xhci_hcd
272:          1  XIVE-IRQ 4368 Edge      hvc_console
LOC:      10508   Local timer interrupts for timer event device
BCT:          0   Broadcast timer interrupts for timer event device
LOC:          0   Local timer interrupts for others
SPU:          5   Spurious interrupts
PMI:          0   Performance monitoring interrupts
MCE:          0   Machine check exceptions
NMI:          0   System Reset interrupts
DBL:          0   Doorbell interrupts


and 7bfc759c02b8 "spapr/xive: add state synchronization with KVM" works:

           CPU0
 16:          0  XIVE-IPI   0 Edge      IPI
 19:          0  XIVE-IRQ 4610 Level     NPU Device
 20:          0  XIVE-IRQ 4611 Level     NPU Device
 21:          0  XIVE-IRQ 4096 Edge      RAS_EPOW
 22:          0  XIVE-IRQ 4097 Edge      RAS_HOTPLUG
257:      11833  XIVE-IRQ 4353 Edge      ibmvscsi
258:          0  XIVE-IRQ 4864 Edge      virtio0-config
259:       1632  XIVE-IRQ 4865 Edge      virtio0-input.0
260:          1  XIVE-IRQ 4866 Edge      virtio0-output.0
261:          0  XIVE-IRQ 4868 Edge      xhci_hcd
262:          0  XIVE-IRQ 4869 Edge      xhci_hcd
263:         60  XIVE-IRQ 4867 Edge      nvidia
272:          0  XIVE-IRQ 4368 Edge      hvc_console
LOC:       2236   Local timer interrupts for timer event device
BCT:          0   Broadcast timer interrupts for timer event device
LOC:          0   Local timer interrupts for others
SPU:          2   Spurious interrupts
PMI:          0   Performance monitoring interrupts
MCE:          0   Machine check exceptions
NMI:          0   System Reset interrupts
DBL:          0   Doorbell interrupts



Here is the command line:

/home/aik/pbuild/qemu-aikrhel74alt-ppc64/ppc64-softmmu/qemu-system-ppc64 \
-nodefaults \
-chardev stdio,id=STDIO0,signal=off,mux=on \
-device spapr-vty,id=svty0,reg=0x71000110,chardev=STDIO0 \
-mon id=MON0,chardev=STDIO0,mode=readline -nographic -vga none \
-enable-kvm \
-device nec-usb-xhci,id=nec-usb-xhci0 -m 16G \
-netdev "user,id=USER0,hostfwd=tcp::2223-:22" \
-device "virtio-net-pci,id=vnet0,mac=C0:41:49:4b:00:00,netdev=USER0" \
img/u1804-64G-cuda10.1-418.67-swiotlb.qcow2 \
-machine pseries,cap-cfpc=broken,cap-htm=off,ic-mode=xive \
-device "vfio-pci,id=vfio0006_00_00_1,host=0006:00:00.1" \
-device "vfio-pci,id=vfio0006_00_00_0,host=0006:00:00.0" \
-device "vfio-pci,id=vfio0004_04_00_0,host=0004:04:00.0" \
-kernel ./vmldbg -append "root=/dev/sda2 console=hvc0 debug loglevel=8" \
-snapshot \
-smp 1,threads=1 -bios ./slof.bin \
-L /home/aik/t/qemu-ppc64-bios/ \
-trace events=qemu_trace_events -d guest_errors \
-chardev socket,id=SOCKET0,server,nowait,path=qemu.mon.user2223.6_0_0_1 \
-mon chardev=SOCKET0,mode=control




> ---
>  hw/intc/spapr_xive_kvm.c    | 96 ++++++++++++++++++++++++++++++++++++-
>  include/hw/ppc/spapr_xive.h |  1 +
>  2 files changed, 96 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/intc/spapr_xive_kvm.c b/hw/intc/spapr_xive_kvm.c
> index 8dd4f96e0b..735577a6f8 100644
> --- a/hw/intc/spapr_xive_kvm.c
> +++ b/hw/intc/spapr_xive_kvm.c
> @@ -433,9 +433,100 @@ static void kvmppc_xive_get_queues(SpaprXive *xive, Error **errp)
>      }
>  }
>  
> +/*
> + * The primary goal of the XIVE VM change handler is to mark the EQ
> + * pages dirty when all XIVE event notifications have stopped.
> + *
> + * Whenever the VM is stopped, the VM change handler sets the source
> + * PQs to PENDING to stop the flow of events and to possibly catch a
> + * triggered interrupt occuring while the VM is stopped. The previous
> + * state is saved in anticipation of a migration. The XIVE controller
> + * is then synced through KVM to flush any in-flight event
> + * notification and stabilize the EQs.
> + *
> + * At this stage, we can mark the EQ page dirty and let a migration
> + * sequence transfer the EQ pages to the destination, which is done
> + * just after the stop state.
> + *
> + * The previous configuration of the sources is restored when the VM
> + * runs again. If an interrupt was queued while the VM was stopped,
> + * simply generate a trigger.
> + */
> +static void kvmppc_xive_change_state_handler(void *opaque, int running,
> +                                             RunState state)
> +{
> +    SpaprXive *xive = opaque;
> +    XiveSource *xsrc = &xive->source;
> +    Error *local_err = NULL;
> +    int i;
> +
> +    /*
> +     * Restore the sources to their initial state. This is called when
> +     * the VM resumes after a stop or a migration.
> +     */
> +    if (running) {
> +        for (i = 0; i < xsrc->nr_irqs; i++) {
> +            uint8_t pq = xive_source_esb_get(xsrc, i);
> +            uint8_t old_pq;
> +
> +            old_pq = xive_esb_read(xsrc, i, XIVE_ESB_SET_PQ_00 + (pq << 8));
> +
> +            /*
> +             * An interrupt was queued while the VM was stopped,
> +             * generate a trigger.
> +             */
> +            if (pq == XIVE_ESB_RESET && old_pq == XIVE_ESB_QUEUED) {
> +                xive_esb_trigger(xsrc, i);
> +            }
> +        }
> +
> +        return;
> +    }
> +
> +    /*
> +     * Mask the sources, to stop the flow of event notifications, and
> +     * save the PQs locally in the XiveSource object. The XiveSource
> +     * state will be collected later on by its vmstate handler if a
> +     * migration is in progress.
> +     */
> +    for (i = 0; i < xsrc->nr_irqs; i++) {
> +        uint8_t pq = xive_esb_read(xsrc, i, XIVE_ESB_GET);
> +
> +        /*
> +         * PQ is set to PENDING to possibly catch a triggered
> +         * interrupt occuring while the VM is stopped (hotplug event
> +         * for instance) .
> +         */
> +        if (pq != XIVE_ESB_OFF) {
> +            pq = xive_esb_read(xsrc, i, XIVE_ESB_SET_PQ_10);
> +        }
> +        xive_source_esb_set(xsrc, i, pq);
> +    }
> +
> +    /*
> +     * Sync the XIVE controller in KVM, to flush in-flight event
> +     * notification that should be enqueued in the EQs and mark the
> +     * XIVE EQ pages dirty to collect all updates.
> +     */
> +    kvm_device_access(xive->fd, KVM_DEV_XIVE_GRP_CTRL,
> +                      KVM_DEV_XIVE_EQ_SYNC, NULL, true, &local_err);
> +    if (local_err) {
> +        error_report_err(local_err);
> +        return;
> +    }
> +}
> +
>  void kvmppc_xive_synchronize_state(SpaprXive *xive, Error **errp)
>  {
> -    kvmppc_xive_source_get_state(&xive->source);
> +    /*
> +     * When the VM is stopped, the sources are masked and the previous
> +     * state is saved in anticipation of a migration. We should not
> +     * synchronize the source state in that case else we will override
> +     * the saved state.
> +     */
> +    if (runstate_is_running()) {
> +        kvmppc_xive_source_get_state(&xive->source);
> +    }
>  
>      /* EAT: there is no extra state to query from KVM */
>  
> @@ -515,6 +606,9 @@ void kvmppc_xive_connect(SpaprXive *xive, Error **errp)
>                                        "xive.tima", tima_len, xive->tm_mmap);
>      sysbus_init_mmio(SYS_BUS_DEVICE(xive), &xive->tm_mmio);
>  
> +    xive->change = qemu_add_vm_change_state_handler(
> +        kvmppc_xive_change_state_handler, xive);
> +
>      kvm_kernel_irqchip = true;
>      kvm_msi_via_irqfd_allowed = true;
>      kvm_gsi_direct_mapping = true;
> diff --git a/include/hw/ppc/spapr_xive.h b/include/hw/ppc/spapr_xive.h
> index 7e49badd8c..734662c12a 100644
> --- a/include/hw/ppc/spapr_xive.h
> +++ b/include/hw/ppc/spapr_xive.h
> @@ -42,6 +42,7 @@ typedef struct SpaprXive {
>      /* KVM support */
>      int           fd;
>      void          *tm_mmap;
> +    VMChangeStateEntry *change;
>  } SpaprXive;
>  
>  /*
> 

-- 
Alexey