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

[Greg Kurz]

On Thu, 6 Aug 2020 15:08:35 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Aug 05, 2020 at 07:35:37PM +0200, 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. Introduce helpers to access the underlying
> > fd for various XIVE types and call them with a kvm_irqchip_in_kernel()
> > guard : this allows the compiler to optimize the kvmppc_xive_* calls
> > out if CONFIG_KVM isn't defined, thus avoiding the need for stubs.
> > 
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> >  hw/intc/spapr_xive.c        |   39 +++++++++++++++++++++++++--------------
> >  hw/intc/spapr_xive_kvm.c    |   15 +++++++++++++++
> >  hw/intc/xive.c              |   30 +++++++++++++++++++++++-------
> >  include/hw/ppc/spapr_xive.h |    1 +
> >  include/hw/ppc/xive.h       |    2 ++
> >  5 files changed, 66 insertions(+), 21 deletions(-)
> > 
> > diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
> > index 89c8cd96670b..98e6489fb16d 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 kvmppc_xive_in_kernel(xive) \
> > +    (kvm_irqchip_in_kernel() && kvmppc_xive_kernel_irqchip(xive))
> 
> This all seems like a good idea, my only concern is that the semantic
> difference between kvmppc_xive_in_kernel() and
> kvmppc_xive_kernel_irqchip() is pretty subtle and non-obvious (and
> likewise for the tctx and xsrc variations).
> 

Yeah, kvmppc_xive_in_kernel() and friends are essentially versions
that also work when CONFIG_KVM is not set (needed to build
qemu-system-ppc64 for non-POWER hosts).

> We're right in the XIVE implementation, so I suggest you eliminate the
> kvmppc_xive_kernel_irqchip() etc. wrappers and just open code a check
> on the fd in kvmppc_xive_in_kernel() etc.
> 

This is true for the kvmppc_xive_in_kernel() variant that takes a
SpaprXive * arg. Things are different for the tctx and xsrc
variants, because xive.c is platform agnostic (shared between
spapr and powernv). Exposing the SpaprXive type to xive.c
would look like a layering violation to me.

Maybe introducing abstract class methods at the base XIVE level (eg.
XivePresenterClass) and implement them in platform-specific code
would make things clearer ?

> > +
> >  void spapr_xive_pic_print_info(SpaprXive *xive, Monitor *mon)
> >  {
> >      XiveSource *xsrc = &xive->source;
> >      int i;
> >  
> > -    if (kvm_irqchip_in_kernel()) {
> > +    if (kvmppc_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 (kvmppc_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 (kvmppc_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 (kvmppc_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 (kvmppc_xive_in_kernel(xive)) {
> >          kvmppc_xive_source_set_irq(&xive->source, irq, val);
> >      } else {
> >          xive_source_set_irq(&xive->source, irq, val);
> > @@ -749,7 +760,7 @@ static void 
> > spapr_xive_deactivate(SpaprInterruptController *intc)
> >  
> >      spapr_xive_mmio_set_enabled(xive, false);
> >  
> > -    if (kvm_irqchip_in_kernel()) {
> > +    if (kvmppc_xive_in_kernel(xive)) {
> >          kvmppc_xive_disconnect(intc);
> >      }
> >  }
> > @@ -1058,7 +1069,7 @@ 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 (kvmppc_xive_in_kernel(xive)) {
> >          Error *local_err = NULL;
> >  
> >          kvmppc_xive_set_source_config(xive, lisn, &new_eas, &local_err);
> > @@ -1379,7 +1390,7 @@ static target_ulong h_int_set_queue_config(PowerPCCPU 
> > *cpu,
> >       */
> >  
> >  out:
> > -    if (kvm_irqchip_in_kernel()) {
> > +    if (kvmppc_xive_in_kernel(xive)) {
> >          Error *local_err = NULL;
> >  
> >          kvmppc_xive_set_queue_config(xive, end_blk, end_idx, &end, 
> > &local_err);
> > @@ -1480,7 +1491,7 @@ static target_ulong h_int_get_queue_config(PowerPCCPU 
> > *cpu,
> >          args[2] = 0;
> >      }
> >  
> > -    if (kvm_irqchip_in_kernel()) {
> > +    if (kvmppc_xive_in_kernel(xive)) {
> >          Error *local_err = NULL;
> >  
> >          kvmppc_xive_get_queue_config(xive, end_blk, end_idx, end, 
> > &local_err);
> > @@ -1642,7 +1653,7 @@ static target_ulong h_int_esb(PowerPCCPU *cpu,
> >          return H_P3;
> >      }
> >  
> > -    if (kvm_irqchip_in_kernel()) {
> > +    if (kvmppc_xive_in_kernel(xive)) {
> >          args[0] = kvmppc_xive_esb_rw(xsrc, lisn, offset, data,
> >                                       flags & SPAPR_XIVE_ESB_STORE);
> >      } else {
> > @@ -1717,7 +1728,7 @@ static target_ulong h_int_sync(PowerPCCPU *cpu,
> >       * under KVM
> >       */
> >  
> > -    if (kvm_irqchip_in_kernel()) {
> > +    if (kvmppc_xive_in_kernel(xive)) {
> >          Error *local_err = NULL;
> >  
> >          kvmppc_xive_sync_source(xive, lisn, &local_err);
> > @@ -1761,7 +1772,7 @@ static target_ulong h_int_reset(PowerPCCPU *cpu,
> >  
> >      device_legacy_reset(DEVICE(xive));
> >  
> > -    if (kvm_irqchip_in_kernel()) {
> > +    if (kvmppc_xive_in_kernel(xive)) {
> >          Error *local_err = NULL;
> >  
> >          kvmppc_xive_reset(xive, &local_err);
> > diff --git a/hw/intc/spapr_xive_kvm.c b/hw/intc/spapr_xive_kvm.c
> > index 893a1ee77e70..a9657e2b0cda 100644
> > --- a/hw/intc/spapr_xive_kvm.c
> > +++ b/hw/intc/spapr_xive_kvm.c
> > @@ -889,3 +889,18 @@ void kvmppc_xive_disconnect(SpaprInterruptController 
> > *intc)
> >          xive->change = NULL;
> >      }
> >  }
> > +
> > +bool kvmppc_xive_kernel_irqchip(SpaprXive *xive)
> > +{
> > +    return xive->fd != -1;
> > +}
> > +
> > +bool kvmppc_xive_kernel_irqchip_tctx(XiveTCTX *tctx)
> > +{
> > +    return kvmppc_xive_kernel_irqchip(SPAPR_XIVE(tctx->xptr));
> > +}
> > +
> > +bool kvmppc_xive_kernel_irqchip_xsrc(XiveSource *xsrc)
> > +{
> > +    return kvmppc_xive_kernel_irqchip(SPAPR_XIVE(xsrc->xive));
> > +}
> > diff --git a/hw/intc/xive.c b/hw/intc/xive.c
> > index 9b55e0356c62..2e1af4530dc5 100644
> > --- a/hw/intc/xive.c
> > +++ b/hw/intc/xive.c
> > @@ -592,6 +592,13 @@ 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 kvmppc_xive_in_kernel_tctx(tctx) \
> > +    (kvm_irqchip_in_kernel() && kvmppc_xive_kernel_irqchip_tctx(tctx))
> > +
> >  void xive_tctx_pic_print_info(XiveTCTX *tctx, Monitor *mon)
> >  {
> >      int cpu_index;
> > @@ -606,7 +613,7 @@ 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 (kvmppc_xive_in_kernel_tctx(tctx)) {
> >          Error *local_err = NULL;
> >  
> >          kvmppc_xive_cpu_synchronize_state(tctx, &local_err);
> > @@ -671,7 +678,7 @@ 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 (kvmppc_xive_in_kernel_tctx(tctx)) {
> >          kvmppc_xive_cpu_connect(tctx, &local_err);
> >          if (local_err) {
> >              error_propagate(errp, local_err);
> > @@ -682,10 +689,11 @@ 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 (kvmppc_xive_in_kernel_tctx(tctx)) {
> > +        kvmppc_xive_cpu_get_state(tctx, &local_err);
> >          if (local_err) {
> >              error_report_err(local_err);
> >              return -1;
> > @@ -697,14 +705,15 @@ 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 (kvmppc_xive_in_kernel_tctx(tctx)) {
> >          /*
> >           * 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;
> > @@ -1125,6 +1134,13 @@ static void xive_source_reset(void *dev)
> >      memset(xsrc->status, XIVE_ESB_OFF, xsrc->nr_irqs);
> >  }
> >  
> > +/*
> > + * kvm_irqchip_in_kernel() will cause the compiler to turn this
> > + * info a nop if CONFIG_KVM isn't defined.
> > + */
> > +#define kvmppc_xive_in_kernel_xsrc(xsrc) \
> > +    (kvm_irqchip_in_kernel() && kvmppc_xive_kernel_irqchip_xsrc(xsrc))
> > +
> >  static void xive_source_realize(DeviceState *dev, Error **errp)
> >  {
> >      XiveSource *xsrc = XIVE_SOURCE(dev);
> > @@ -1147,7 +1163,7 @@ 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 (!kvmppc_xive_in_kernel_xsrc(xsrc)) {
> >          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/spapr_xive.h b/include/hw/ppc/spapr_xive.h
> > index 93d09d68deb7..9fd00378ac1f 100644
> > --- a/include/hw/ppc/spapr_xive.h
> > +++ b/include/hw/ppc/spapr_xive.h
> > @@ -94,5 +94,6 @@ void kvmppc_xive_get_queue_config(SpaprXive *xive, 
> > uint8_t end_blk,
> >  void kvmppc_xive_synchronize_state(SpaprXive *xive, Error **errp);
> >  int kvmppc_xive_pre_save(SpaprXive *xive);
> >  int kvmppc_xive_post_load(SpaprXive *xive, int version_id);
> > +bool kvmppc_xive_kernel_irqchip(SpaprXive *xive);
> >  
> >  #endif /* PPC_SPAPR_XIVE_H */
> > diff --git a/include/hw/ppc/xive.h b/include/hw/ppc/xive.h
> > index 705cf48176fc..ea66e9ea9c7b 100644
> > --- a/include/hw/ppc/xive.h
> > +++ b/include/hw/ppc/xive.h
> > @@ -484,5 +484,7 @@ void kvmppc_xive_cpu_connect(XiveTCTX *tctx, Error 
> > **errp);
> >  void kvmppc_xive_cpu_synchronize_state(XiveTCTX *tctx, Error **errp);
> >  void kvmppc_xive_cpu_get_state(XiveTCTX *tctx, Error **errp);
> >  void kvmppc_xive_cpu_set_state(XiveTCTX *tctx, Error **errp);
> > +bool kvmppc_xive_kernel_irqchip_tctx(XiveTCTX *tctx);
> > +bool kvmppc_xive_kernel_irqchip_xsrc(XiveSource *xsrc);
> >  
> >  #endif /* PPC_XIVE_H */
> > 
> > 
>

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