Re: [Qemu-devel] [PATCH 13/13] spapr: add KVM support to the 'dual' machine

["Cédric Le Goater" <clg@kaod.org>]

On 2/13/19 2:32 AM, David Gibson wrote:
> On Tue, Feb 12, 2019 at 08:18:19AM +0100, Cédric Le Goater wrote:
>> On 2/12/19 2:11 AM, David Gibson wrote:
>>> On Mon, Jan 07, 2019 at 07:39:46PM +0100, Cédric Le Goater wrote:
>>>> The interrupt mode is chosen by the CAS negotiation process and
>>>> activated after a reset to take into account the required changes in
>>>> the machine. This brings new constraints on how the associated KVM IRQ
>>>> device is initialized.
>>>>
>>>> Currently, each model takes care of the initialization of the KVM
>>>> device in their realize method but this is not possible anymore as the
>>>> initialization needs to be done globaly when the interrupt mode is
>>>> known, i.e. when machine is reseted. It also means that we need a way
>>>> to delete a KVM device when another mode is chosen.
>>>>
>>>> Also, to support migration, the QEMU objects holding the state to
>>>> transfer should always be available but not necessarily activated.
>>>>
>>>> The overall approach of this proposal is to initialize both interrupt
>>>> mode at the QEMU level and keep the IRQ number space in sync to allow
>>>> switching from one mode to another. For the KVM side of things, the
>>>> whole initialization of the KVM device, sources and presenters, is
>>>> grouped in a single routine. The XICS and XIVE sPAPR IRQ reset
>>>> handlers are modified accordingly to handle the init and the delete
>>>> sequences of the KVM device.
>>>>
>>>> As KVM is now initialized at reset, we loose the possiblity to
>>>> fallback to the QEMU emulated mode in case of failure and failures
>>>> become fatal to the machine.
>>>>
>>>> Signed-off-by: Cédric Le Goater <clg@kaod.org>
>>>> ---
>>>>  hw/intc/spapr_xive.c     |  8 +---
>>>>  hw/intc/spapr_xive_kvm.c | 27 ++++++++++++++
>>>>  hw/intc/xics_kvm.c       | 25 +++++++++++++
>>>>  hw/intc/xive.c           |  4 --
>>>>  hw/ppc/spapr_irq.c       | 79 ++++++++++++++++++++++++++++------------
>>>>  5 files changed, 109 insertions(+), 34 deletions(-)
>>>>
>>>> diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
>>>> index 21f3c1ef0901..0661aca35900 100644
>>>> --- a/hw/intc/spapr_xive.c
>>>> +++ b/hw/intc/spapr_xive.c
>>>> @@ -330,13 +330,7 @@ static void spapr_xive_realize(DeviceState *dev, Error **errp)
>>>>      xive->eat = g_new0(XiveEAS, xive->nr_irqs);
>>>>      xive->endt = g_new0(XiveEND, xive->nr_ends);
>>>>  
>>>> -    if (kvmppc_xive_enabled()) {
>>>> -        kvmppc_xive_connect(xive, &local_err);
>>>> -        if (local_err) {
>>>> -            error_propagate(errp, local_err);
>>>> -            return;
>>>> -        }
>>>> -    } else {
>>>> +    if (!kvmppc_xive_enabled()) {
>>>>          /* TIMA initialization */
>>>>          memory_region_init_io(&xive->tm_mmio, OBJECT(xive), &xive_tm_ops, xive,
>>>>                                "xive.tima", 4ull << TM_SHIFT);
>>>> diff --git a/hw/intc/spapr_xive_kvm.c b/hw/intc/spapr_xive_kvm.c
>>>> index d35814c1992e..3ebc947f2be7 100644
>>>> --- a/hw/intc/spapr_xive_kvm.c
>>>> +++ b/hw/intc/spapr_xive_kvm.c
>>>> @@ -737,6 +737,15 @@ void kvmppc_xive_connect(sPAPRXive *xive, Error **errp)
>>>>      Error *local_err = NULL;
>>>>      size_t esb_len;
>>>>      size_t tima_len;
>>>> +    CPUState *cs;
>>>> +
>>>> +    /*
>>>> +     * The KVM XIVE device already in use. This is the case when
>>>> +     * rebooting XIVE -> XIVE
>>>
>>> Can this case actually occur?  Further down you appear to
>>> unconditionally destroy both KVM devices at reset time.
>>
>> I guess you are right. I will check.
>>
>>>> +     */
>>>> +    if (xive->fd != -1) {
>>>> +        return;
>>>> +    }
>>>>  
>>>>      if (!kvm_enabled() || !kvmppc_has_cap_xive()) {
>>>>          error_setg(errp, "IRQ_XIVE capability must be present for KVM");
>>>> @@ -800,6 +809,24 @@ void kvmppc_xive_connect(sPAPRXive *xive, Error **errp)
>>>>      xive->change = qemu_add_vm_change_state_handler(
>>>>          kvmppc_xive_change_state_handler, xive);
>>>>  
>>>> +    /* Connect the presenters to the initial VCPUs of the machine */
>>>> +    CPU_FOREACH(cs) {
>>>> +        PowerPCCPU *cpu = POWERPC_CPU(cs);
>>>> +
>>>> +        kvmppc_xive_cpu_connect(cpu->tctx, &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            return;
>>>> +        }
>>>> +    }
>>>> +
>>>> +    /* Update the KVM sources */
>>>> +    kvmppc_xive_source_reset(xsrc, &local_err);
>>>> +    if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            return;
>>>> +    }
>>>> +
>>>>      kvm_kernel_irqchip = true;
>>>>      kvm_msi_via_irqfd_allowed = true;
>>>>      kvm_gsi_direct_mapping = true;
>>>> diff --git a/hw/intc/xics_kvm.c b/hw/intc/xics_kvm.c
>>>> index 1d21ff217b82..bfc35d71df7f 100644
>>>> --- a/hw/intc/xics_kvm.c
>>>> +++ b/hw/intc/xics_kvm.c
>>>> @@ -448,6 +448,16 @@ static void rtas_dummy(PowerPCCPU *cpu, sPAPRMachineState *spapr,
>>>>  int xics_kvm_init(sPAPRMachineState *spapr, Error **errp)
>>>>  {
>>>>      int rc;
>>>> +    CPUState *cs;
>>>> +    Error *local_err = NULL;
>>>> +
>>>> +    /*
>>>> +     * The KVM XICS device already in use. This is the case when
>>>> +     * rebooting XICS -> XICS
>>>> +     */
>>>> +    if (kernel_xics_fd != -1) {
>>>> +        return 0;
>>>> +    }
>>>>  
>>>>      if (!kvm_enabled() || !kvm_check_extension(kvm_state, KVM_CAP_IRQ_XICS)) {
>>>>          error_setg(errp,
>>>> @@ -496,6 +506,21 @@ int xics_kvm_init(sPAPRMachineState *spapr, Error **errp)
>>>>      kvm_msi_via_irqfd_allowed = true;
>>>>      kvm_gsi_direct_mapping = true;
>>>>  
>>>> +    /* Connect the presenters to the initial VCPUs of the machine */
>>>> +    CPU_FOREACH(cs) {
>>>> +        PowerPCCPU *cpu = POWERPC_CPU(cs);
>>>> +
>>>> +        icp_kvm_connect(cpu->icp, &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            goto fail;
>>>> +        }
>>>> +        icp_set_kvm_state(cpu->icp, 1);
>>>> +    }
>>>> +
>>>> +    /* Update the KVM sources */
>>>> +    ics_set_kvm_state(ICS_KVM(spapr->ics), 1);
>>>> +
>>>>      return 0;
>>>>  
>>>>  fail:
>>>> diff --git a/hw/intc/xive.c b/hw/intc/xive.c
>>>> index c5c2fbc3f8bc..c166eab5b210 100644
>>>> --- a/hw/intc/xive.c
>>>> +++ b/hw/intc/xive.c
>>>> @@ -932,10 +932,6 @@ static void xive_source_reset(void *dev)
>>>>  
>>>>      /* PQs are initialized to 0b01 (Q=1) which corresponds to "ints off" */
>>>>      memset(xsrc->status, XIVE_ESB_OFF, xsrc->nr_irqs);
>>>> -
>>>> -    if (kvmppc_xive_enabled()) {
>>>> -        kvmppc_xive_source_reset(xsrc, &error_fatal);
>>>> -    }
>>>>  }
>>>>  
>>>>  static void xive_source_realize(DeviceState *dev, Error **errp)
>>>> diff --git a/hw/ppc/spapr_irq.c b/hw/ppc/spapr_irq.c
>>>> index ba27d9d8e972..5592eec3787b 100644
>>>> --- a/hw/ppc/spapr_irq.c
>>>> +++ b/hw/ppc/spapr_irq.c
>>>> @@ -98,20 +98,14 @@ static void spapr_irq_init_xics(sPAPRMachineState *spapr, Error **errp)
>>>>      int nr_irqs = spapr->irq->nr_irqs;
>>>>      Error *local_err = NULL;
>>>>  
>>>> -    if (kvm_enabled()) {
>>>> -        if (machine_kernel_irqchip_allowed(machine) &&
>>>> -            !xics_kvm_init(spapr, &local_err)) {
>>>> -            spapr->icp_type = TYPE_KVM_ICP;
>>>> -            spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs,
>>>> -                                          &local_err);
>>>> -        }
>>>> -        if (machine_kernel_irqchip_required(machine) && !spapr->ics) {
>>>> -            error_prepend(&local_err,
>>>> -                          "kernel_irqchip requested but unavailable: ");
>>>> -            goto error;
>>>
>>> I don't see anything that replaces the irqchip_required logic, which
>>> doesn't seem right.
>>
>> Yes. We do loose the ability to fall back to the emulated device in case
>> of failure. It is not impossible to do but it will require more changes
>> to check what are the KVM capabilities before starting the machine.
> 
> Uh... it seems more like it's the other way around.  We'll always fall
> back to emulated, even if we've explicitly said on the command line
> that we don't want that.

Ah yes. The init function might be also broken. 

XICS mode is a bit more difficult to handle than XIVE because we have 
different object type for the KVM device and the QEMU emulated device, 
and with the 'dual' mode, we activate the device at CAS reset time.

Failures being handled at reset time, should we keep the same logic and  
abort the machine at reset if the kernel irqchip is required ? 

But we won't be able to fall back on the QEMU emulated device if KVM 
XICS fails and if the kernel irqchip is only allowed. It should work for 
XIVE though.

Thanks,

C.


>> Nevertheless, any failure in reset when setting the KVM backend will
>> result in machine abort.
>>
>> C.       
>>
>>>
>>>> +    if (kvm_enabled() && machine_kernel_irqchip_allowed(machine)) {
>>>> +        spapr->icp_type = TYPE_KVM_ICP;
>>>> +        spapr->ics = spapr_ics_create(spapr, TYPE_ICS_KVM, nr_irqs,
>>>> +                                      &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            return;
>>>>          }
>>>> -        error_free(local_err);
>>>> -        local_err = NULL;
>>>>      }
>>>>  
>>>>      if (!spapr->ics) {
>>>> @@ -119,10 +113,11 @@ static void spapr_irq_init_xics(sPAPRMachineState *spapr, Error **errp)
>>>>          spapr->icp_type = TYPE_ICP;
>>>>          spapr->ics = spapr_ics_create(spapr, TYPE_ICS_SIMPLE, nr_irqs,
>>>>                                        &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            return;
>>>> +        }
>>>>      }
>>>> -
>>>> -error:
>>>> -    error_propagate(errp, local_err);
>>>>  }
>>>>  
>>>>  #define ICS_IRQ_FREE(ics, srcno)   \
>>>> @@ -233,7 +228,17 @@ static void spapr_irq_set_irq_xics(void *opaque, int srcno, int val)
>>>>  
>>>>  static void spapr_irq_reset_xics(sPAPRMachineState *spapr, Error **errp)
>>>>  {
>>>> -    /* TODO: create the KVM XICS device */
>>>> +    MachineState *machine = MACHINE(spapr);
>>>> +    Error *local_err = NULL;
>>>> +
>>>> +    if (kvm_enabled() && machine_kernel_irqchip_allowed(machine)) {
>>>> +        xics_kvm_init(spapr, &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            error_prepend(errp, "KVM XICS connect failed: ");
>>>> +            return;
>>>> +        }
>>>> +    }
>>>>  }
>>>>  
>>>>  #define SPAPR_IRQ_XICS_NR_IRQS     0x1000
>>>> @@ -393,6 +398,7 @@ static int spapr_irq_post_load_xive(sPAPRMachineState *spapr, int version_id)
>>>>  static void spapr_irq_reset_xive(sPAPRMachineState *spapr, Error **errp)
>>>>  {
>>>>      CPUState *cs;
>>>> +    Error *local_err = NULL;
>>>>  
>>>>      CPU_FOREACH(cs) {
>>>>          PowerPCCPU *cpu = POWERPC_CPU(cs);
>>>> @@ -401,6 +407,15 @@ static void spapr_irq_reset_xive(sPAPRMachineState *spapr, Error **errp)
>>>>          spapr_xive_set_tctx_os_cam(cpu->tctx);
>>>>      }
>>>>  
>>>> +    if (kvmppc_xive_enabled()) {
>>>> +        kvmppc_xive_connect(spapr->xive, &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            error_prepend(errp, "KVM XIVE connect failed: ");
>>>> +            return;
>>>> +        }
>>>> +    }
>>>> +
>>>>      /* Activate the XIVE MMIOs */
>>>>      spapr_xive_mmio_set_enabled(spapr->xive, true);
>>>>  }
>>>> @@ -462,14 +477,8 @@ static sPAPRIrq *spapr_irq_current(sPAPRMachineState *spapr)
>>>>  
>>>>  static void spapr_irq_init_dual(sPAPRMachineState *spapr, Error **errp)
>>>>  {
>>>> -    MachineState *machine = MACHINE(spapr);
>>>>      Error *local_err = NULL;
>>>>  
>>>> -    if (kvm_enabled() && machine_kernel_irqchip_allowed(machine)) {
>>>> -        error_setg(errp, "No KVM support for the 'dual' machine");
>>>> -        return;
>>>> -    }
>>>> -
>>>>      spapr_irq_xics.init(spapr, &local_err);
>>>>      if (local_err) {
>>>>          error_propagate(errp, local_err);
>>>> @@ -568,11 +577,16 @@ static void spapr_irq_cpu_intc_create_dual(sPAPRMachineState *spapr,
>>>>  
>>>>  static int spapr_irq_post_load_dual(sPAPRMachineState *spapr, int version_id)
>>>>  {
>>>> +    MachineState *machine = MACHINE(spapr);
>>>> +
>>>>      /*
>>>>       * Force a reset of the XIVE backend after migration. The machine
>>>>       * defaults to XICS at startup.
>>>>       */
>>>>      if (spapr_ovec_test(spapr->ov5_cas, OV5_XIVE_EXPLOIT)) {
>>>> +        if (kvm_enabled() && machine_kernel_irqchip_allowed(machine)) {
>>>> +            xics_kvm_disconnect(spapr, &error_fatal);
>>>> +        }
>>>>          spapr_irq_xive.reset(spapr, &error_fatal);
>>>>      }
>>>>  
>>>> @@ -581,12 +595,31 @@ static int spapr_irq_post_load_dual(sPAPRMachineState *spapr, int version_id)
>>>>  
>>>>  static void spapr_irq_reset_dual(sPAPRMachineState *spapr, Error **errp)
>>>>  {
>>>> +    MachineState *machine = MACHINE(spapr);
>>>> +    Error *local_err = NULL;
>>>> +
>>>>      /*
>>>>       * Deactivate the XIVE MMIOs. The XIVE backend will reenable them
>>>>       * if selected.
>>>>       */
>>>>      spapr_xive_mmio_set_enabled(spapr->xive, false);
>>>>  
>>>> +    /* Destroy all KVM devices */
>>>> +    if (kvm_enabled() && machine_kernel_irqchip_allowed(machine)) {
>>>> +        xics_kvm_disconnect(spapr, &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            error_prepend(errp, "KVM XICS disconnect failed: ");
>>>> +            return;
>>>> +        }
>>>> +        kvmppc_xive_disconnect(spapr->xive, &local_err);
>>>> +        if (local_err) {
>>>> +            error_propagate(errp, local_err);
>>>> +            error_prepend(errp, "KVM XIVE disconnect failed: ");
>>>> +            return;
>>>> +        }
>>>> +    }
>>>> +
>>>>      spapr_irq_current(spapr)->reset(spapr, errp);
>>>>  }
>>>>  
>>>
>>
>