Re: [PATCH v2 for-5.2 3/5] ppc/xive: Introduce dedicated kvm_irqchip_in_kernel() wrappers

["Cédric Le Goater" <clg@kaod.org>]

On 8/6/20 6:56 PM, Greg Kurz wrote:
> Calls to the KVM XIVE device are guarded by kvm_irqchip_in_kernel(). This
> ensures that QEMU won't try to use the device if KVM is disabled or if
> an in-kernel irqchip isn't required.
> 
> When using ic-mode=dual with the pseries machine, we have two possible
> interrupt controllers: XIVE and XICS. The kvm_irqchip_in_kernel() helper
> will return true as soon as any of the KVM device is created. It might
> lure QEMU to think that the other one is also around, while it is not.
> This is exactly what happens with ic-mode=dual at machine init when
> claiming IRQ numbers, which must be done on all possible IRQ backends,
> eg. RTAS event sources or the PHB0 LSI table : only the KVM XICS device
> is active but we end up calling kvmppc_xive_source_reset_one() anyway,
> which fails. This doesn't cause any trouble because of another bug :
> kvmppc_xive_source_reset_one() lacks an error_setg() and callers don't
> see the failure.
> 
> Most of the other kvmppc_xive_* functions have similar xive->fd
> checks to filter out the case when KVM XIVE isn't active. It
> might look safer to have idempotent functions but it doesn't
> really help to understand what's going on when debugging.
> 
> Since we already have all the kvm_irqchip_in_kernel() in place,
> also have the callers to check xive->fd as well before calling
> KVM XIVE specific code. This is straight-forward for the spapr
> specific XIVE code. Some more care is needed for the platform
> agnostic XIVE code since it cannot access xive->fd directly.
> Introduce new in_kernel() methods in some base XIVE classes
> for this purpose and implement them only in spapr.
> 
> In all cases, we still need to call kvm_irqchip_in_kernel() so that
> compilers can optimize the kvmppc_xive_* calls away when CONFIG_KVM
> isn't defined, thus avoiding the need for stubs.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> v2: Introduce in_kernel() abstract methods in the base XIVE classes
> ---
>  hw/intc/spapr_xive.c  |   53 ++++++++++++++++++++++++++++++++++++-------------
>  hw/intc/xive.c        |   28 +++++++++++++++++++-------
>  include/hw/ppc/xive.h |    2 ++
>  3 files changed, 62 insertions(+), 21 deletions(-)
> 
> diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
> index 89c8cd96670b..cd001c580e89 100644
> --- a/hw/intc/spapr_xive.c
> +++ b/hw/intc/spapr_xive.c
> @@ -148,12 +148,19 @@ static void spapr_xive_end_pic_print_info(SpaprXive *xive, XiveEND *end,
>      xive_end_queue_pic_print_info(end, 6, mon);
>  }
>  
> +/*
> + * kvm_irqchip_in_kernel() will cause the compiler to turn this
> + * info a nop if CONFIG_KVM isn't defined.
> + */
> +#define spapr_xive_in_kernel(xive) \
> +    (kvm_irqchip_in_kernel() && (xive)->fd != -1)
> +

This looks ok. SpaprXive is the userspace frontend device of 
the KVM XIVE native device in the hypervisor.

>  void spapr_xive_pic_print_info(SpaprXive *xive, Monitor *mon)
>  {
>      XiveSource *xsrc = &xive->source;
>      int i;
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          Error *local_err = NULL;
>  
>          kvmppc_xive_synchronize_state(xive, &local_err);
> @@ -507,8 +514,10 @@ static const VMStateDescription vmstate_spapr_xive_eas = {
>  
>  static int vmstate_spapr_xive_pre_save(void *opaque)
>  {
> -    if (kvm_irqchip_in_kernel()) {
> -        return kvmppc_xive_pre_save(SPAPR_XIVE(opaque));
> +    SpaprXive *xive = SPAPR_XIVE(opaque);
> +
> +    if (spapr_xive_in_kernel(xive)) {
> +        return kvmppc_xive_pre_save(xive);
>      }
>  
>      return 0;
> @@ -520,8 +529,10 @@ static int vmstate_spapr_xive_pre_save(void *opaque)
>   */
>  static int spapr_xive_post_load(SpaprInterruptController *intc, int version_id)
>  {
> -    if (kvm_irqchip_in_kernel()) {
> -        return kvmppc_xive_post_load(SPAPR_XIVE(intc), version_id);
> +    SpaprXive *xive = SPAPR_XIVE(intc);
> +
> +    if (spapr_xive_in_kernel(xive)) {
> +        return kvmppc_xive_post_load(xive, version_id);
>      }
>  
>      return 0;
> @@ -564,7 +575,7 @@ static int spapr_xive_claim_irq(SpaprInterruptController *intc, int lisn,
>          xive_source_irq_set_lsi(xsrc, lisn);
>      }
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          return kvmppc_xive_source_reset_one(xsrc, lisn, errp);
>      }
>  
> @@ -641,7 +652,7 @@ static void spapr_xive_set_irq(SpaprInterruptController *intc, int irq, int val)
>  {
>      SpaprXive *xive = SPAPR_XIVE(intc);
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          kvmppc_xive_source_set_irq(&xive->source, irq, val);
>      } else {
>          xive_source_set_irq(&xive->source, irq, val);
> @@ -749,11 +760,21 @@ static void spapr_xive_deactivate(SpaprInterruptController *intc)
>  
>      spapr_xive_mmio_set_enabled(xive, false);
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          kvmppc_xive_disconnect(intc);
>      }
>  }
>  
> +static bool spapr_xive_in_kernel_xptr(const XivePresenter *xptr)
> +{
> +    return spapr_xive_in_kernel(SPAPR_XIVE(xptr));
> +}

This is mostly OK, a XivePresenter is a part of the XiveRouter.

> +static bool spapr_xive_in_kernel_xn(const XiveNotifier *xn)
> +{
> +    return spapr_xive_in_kernel(SPAPR_XIVE(xn));
> +}


This is weird. we have other XiveNotifiers which have no relation
with a kernel backend.

>  static void spapr_xive_class_init(ObjectClass *klass, void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(klass);
> @@ -761,6 +782,7 @@ static void spapr_xive_class_init(ObjectClass *klass, void *data)
>      SpaprInterruptControllerClass *sicc = SPAPR_INTC_CLASS(klass);
>      XivePresenterClass *xpc = XIVE_PRESENTER_CLASS(klass);
>      SpaprXiveClass *sxc = SPAPR_XIVE_CLASS(klass);
> +    XiveNotifierClass *xnc = XIVE_NOTIFIER_CLASS(klass);
>  
>      dc->desc    = "sPAPR XIVE Interrupt Controller";
>      device_class_set_props(dc, spapr_xive_properties);
> @@ -788,6 +810,9 @@ static void spapr_xive_class_init(ObjectClass *klass, void *data)
>      sicc->post_load = spapr_xive_post_load;
>  
>      xpc->match_nvt  = spapr_xive_match_nvt;
> +    xpc->in_kernel  = spapr_xive_in_kernel_xptr;
> +
> +    xnc->in_kernel  = spapr_xive_in_kernel_xn;
>  }
>  
>  static const TypeInfo spapr_xive_info = {
> @@ -1058,7 +1083,7 @@ static target_ulong h_int_set_source_config(PowerPCCPU *cpu,
>          new_eas.w = xive_set_field64(EAS_END_DATA, new_eas.w, eisn);
>      }
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          Error *local_err = NULL;
>  
>          kvmppc_xive_set_source_config(xive, lisn, &new_eas, &local_err);
> @@ -1379,7 +1404,7 @@ static target_ulong h_int_set_queue_config(PowerPCCPU *cpu,
>       */
>  
>  out:
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          Error *local_err = NULL;
>  
>          kvmppc_xive_set_queue_config(xive, end_blk, end_idx, &end, &local_err);
> @@ -1480,7 +1505,7 @@ static target_ulong h_int_get_queue_config(PowerPCCPU *cpu,
>          args[2] = 0;
>      }
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          Error *local_err = NULL;
>  
>          kvmppc_xive_get_queue_config(xive, end_blk, end_idx, end, &local_err);
> @@ -1642,7 +1667,7 @@ static target_ulong h_int_esb(PowerPCCPU *cpu,
>          return H_P3;
>      }
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          args[0] = kvmppc_xive_esb_rw(xsrc, lisn, offset, data,
>                                       flags & SPAPR_XIVE_ESB_STORE);
>      } else {
> @@ -1717,7 +1742,7 @@ static target_ulong h_int_sync(PowerPCCPU *cpu,
>       * under KVM
>       */
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          Error *local_err = NULL;
>  
>          kvmppc_xive_sync_source(xive, lisn, &local_err);
> @@ -1761,7 +1786,7 @@ static target_ulong h_int_reset(PowerPCCPU *cpu,
>  
>      device_legacy_reset(DEVICE(xive));
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (spapr_xive_in_kernel(xive)) {
>          Error *local_err = NULL;
>  
>          kvmppc_xive_reset(xive, &local_err);
> diff --git a/hw/intc/xive.c b/hw/intc/xive.c
> index 9b55e0356c62..27d27fdc9ee4 100644
> --- a/hw/intc/xive.c
> +++ b/hw/intc/xive.c
> @@ -592,6 +592,17 @@ static const char * const xive_tctx_ring_names[] = {
>      "USER", "OS", "POOL", "PHYS",
>  };
>  
> +/*
> + * kvm_irqchip_in_kernel() will cause the compiler to turn this
> + * info a nop if CONFIG_KVM isn't defined.
> + */
> +#define xive_in_kernel(xptr)                                  \
> +    (kvm_irqchip_in_kernel() &&                                         \
> +     ({                                                                 \
> +         XivePresenterClass *xpc = XIVE_PRESENTER_GET_CLASS(xptr);      \
> +         xpc->in_kernel ? xpc->in_kernel(xptr) : false;                 \
> +     }))
> +
>
>  void xive_tctx_pic_print_info(XiveTCTX *tctx, Monitor *mon)
>  {
>      int cpu_index;
> @@ -606,7 +617,7 @@ void xive_tctx_pic_print_info(XiveTCTX *tctx, Monitor *mon)
>  
>      cpu_index = tctx->cs ? tctx->cs->cpu_index : -1;
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (xive_in_kernel(tctx->xptr)) {
>          Error *local_err = NULL;
>  
>          kvmppc_xive_cpu_synchronize_state(tctx, &local_err);
> @@ -671,7 +682,7 @@ static void xive_tctx_realize(DeviceState *dev, Error **errp)
>      }
>  
>      /* Connect the presenter to the VCPU (required for CPU hotplug) */
> -    if (kvm_irqchip_in_kernel()) {
> +    if (xive_in_kernel(tctx->xptr)) {
>          kvmppc_xive_cpu_connect(tctx, &local_err);
>          if (local_err) {
>              error_propagate(errp, local_err);
> @@ -682,10 +693,11 @@ static void xive_tctx_realize(DeviceState *dev, Error **errp)
>  
>  static int vmstate_xive_tctx_pre_save(void *opaque)
>  {
> +    XiveTCTX *tctx = XIVE_TCTX(opaque);
>      Error *local_err = NULL;
>  
> -    if (kvm_irqchip_in_kernel()) {
> -        kvmppc_xive_cpu_get_state(XIVE_TCTX(opaque), &local_err);
> +    if (xive_in_kernel(tctx->xptr)) {
> +        kvmppc_xive_cpu_get_state(tctx, &local_err);
>          if (local_err) {
>              error_report_err(local_err);
>              return -1;
> @@ -697,14 +709,15 @@ static int vmstate_xive_tctx_pre_save(void *opaque)
>  
>  static int vmstate_xive_tctx_post_load(void *opaque, int version_id)
>  {
> +    XiveTCTX *tctx = XIVE_TCTX(opaque);
>      Error *local_err = NULL;
>  
> -    if (kvm_irqchip_in_kernel()) {
> +    if (xive_in_kernel(tctx->xptr)) {
>          /*
>           * Required for hotplugged CPU, for which the state comes
>           * after all states of the machine.
>           */
> -        kvmppc_xive_cpu_set_state(XIVE_TCTX(opaque), &local_err);
> +        kvmppc_xive_cpu_set_state(tctx, &local_err);
>          if (local_err) {
>              error_report_err(local_err);
>              return -1;
> @@ -1128,6 +1141,7 @@ static void xive_source_reset(void *dev)
>  static void xive_source_realize(DeviceState *dev, Error **errp)
>  {
>      XiveSource *xsrc = XIVE_SOURCE(dev);
> +    XiveNotifierClass *xnc = XIVE_NOTIFIER_GET_CLASS(xsrc->xive);
>  
>      assert(xsrc->xive);
>  
> @@ -1147,7 +1161,7 @@ static void xive_source_realize(DeviceState *dev, Error **errp)
>      xsrc->status = g_malloc0(xsrc->nr_irqs);
>      xsrc->lsi_map = bitmap_new(xsrc->nr_irqs);
>  
> -    if (!kvm_irqchip_in_kernel()) {
> +    if (!xnc->in_kernel || !xnc->in_kernel(xsrc->xive)) {
>          memory_region_init_io(&xsrc->esb_mmio, OBJECT(xsrc),
>                                &xive_source_esb_ops, xsrc, "xive.esb",
>                                (1ull << xsrc->esb_shift) * xsrc->nr_irqs);
> diff --git a/include/hw/ppc/xive.h b/include/hw/ppc/xive.h
> index 705cf48176fc..aa46e3fcf512 100644
> --- a/include/hw/ppc/xive.h
> +++ b/include/hw/ppc/xive.h
> @@ -161,6 +161,7 @@ typedef struct XiveNotifier XiveNotifier;
>  typedef struct XiveNotifierClass {
>      InterfaceClass parent;
>      void (*notify)(XiveNotifier *xn, uint32_t lisn);
> +    bool (*in_kernel)(const XiveNotifier *xn);
>  } XiveNotifierClass;
>  
>  /*
> @@ -396,6 +397,7 @@ typedef struct XivePresenterClass {
>                       uint8_t nvt_blk, uint32_t nvt_idx,
>                       bool cam_ignore, uint8_t priority,
>                       uint32_t logic_serv, XiveTCTXMatch *match);
> +    bool (*in_kernel)(const XivePresenter *xptr);
>  } XivePresenterClass;
>  
>  int xive_presenter_tctx_match(XivePresenter *xptr, XiveTCTX *tctx,
> 
> 

It seems redundant. Can we introduce a new XiveBackend QOM interface 
which would implement an in_kernel() handler ? and XiveRouter would 
inherit from it. 

C.