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

[David Gibson]

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).

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.

> +
>  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 */
> 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

signature.asc
Description: PGP signature