Re: [Qemu-devel] [PATCH 08/11] spapr_events: add support for dedicated hotplug event source

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Wed, Oct 12, 2016 at 06:13:56PM -0500, Michael Roth wrote:
> Hotplug events were previously delivered using an EPOW interrupt
> and were queued by linux guests into a circular buffer. For traditional
> EPOW events like shutdown/resets, this isn't an issue, but for hotplug
> events there are cases where this buffer can be exhausted, resulting
> in the loss of hotplug events, resets, etc.
> 
> Newer-style hotplug event are delivered using a dedicated event source.
> We enable this in supported guests by adding standard an additional
> event source in the guest device-tree via /event-sources, and, if
> the guest advertises support for the newer-style hotplug events,
> using the corresponding interrupt to signal the available of
> hotplug/unplug events.
> 
> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> ---
>  hw/ppc/spapr.c         |  10 ++--
>  hw/ppc/spapr_events.c  | 148 ++++++++++++++++++++++++++++++++++++++-----------
>  include/hw/ppc/spapr.h |   3 +-
>  3 files changed, 120 insertions(+), 41 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index d80a6fa..2037222 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -275,8 +275,7 @@ static void *spapr_create_fdt_skel(hwaddr initrd_base,
>                                     hwaddr initrd_size,
>                                     hwaddr kernel_size,
>                                     bool little_endian,
> -                                   const char *kernel_cmdline,
> -                                   uint32_t epow_irq)
> +                                   const char *kernel_cmdline)
>  {
>      void *fdt;
>      uint32_t start_prop = cpu_to_be32(initrd_base);
> @@ -437,7 +436,7 @@ static void *spapr_create_fdt_skel(hwaddr initrd_base,
>      _FDT((fdt_end_node(fdt)));
> 
>      /* event-sources */
> -    spapr_events_fdt_skel(fdt, epow_irq);
> +    spapr_events_fdt_skel(fdt);
> 
>      /* /hypervisor node */
>      if (kvm_enabled()) {
> @@ -1944,7 +1943,7 @@ static void ppc_spapr_init(MachineState *machine)
>      }
>      g_free(filename);
> 
> -    /* Set up EPOW events infrastructure */
> +    /* Set up RTAS event infrastructure */
>      spapr_events_init(spapr);
> 
>      /* Set up the RTC RTAS interfaces */
> @@ -2076,8 +2075,7 @@ static void ppc_spapr_init(MachineState *machine)
>      /* Prepare the device tree */
>      spapr->fdt_skel = spapr_create_fdt_skel(initrd_base, initrd_size,
>                                              kernel_size, kernel_le,
> -                                            kernel_cmdline,
> -                                            spapr->check_exception_irq);
> +                                            kernel_cmdline);
>      assert(spapr->fdt_skel != NULL);
> 
>      /* used by RTAS */
> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
> index 4c7b6ae..f8bbec6 100644
> --- a/hw/ppc/spapr_events.c
> +++ b/hw/ppc/spapr_events.c
> @@ -40,6 +40,7 @@
>  #include "hw/ppc/spapr_drc.h"
>  #include "qemu/help_option.h"
>  #include "qemu/bcd.h"
> +#include "hw/ppc/spapr_ovec.h"
>  #include <libfdt.h>
> 
>  struct rtas_error_log {
> @@ -206,28 +207,104 @@ struct hp_log_full {
>      struct rtas_event_log_v6_hp hp;
>  } QEMU_PACKED;
> 
> -#define EVENT_MASK_INTERNAL_ERRORS           0x80000000
> -#define EVENT_MASK_EPOW                      0x40000000
> -#define EVENT_MASK_HOTPLUG                   0x10000000
> -#define EVENT_MASK_IO                        0x08000000
> +typedef enum EventClassIndex {
> +    EVENT_CLASS_INTERNAL_ERRORS     = 0,
> +    EVENT_CLASS_EPOW                = 1,
> +    EVENT_CLASS_RESERVED            = 2,
> +    EVENT_CLASS_HOT_PLUG            = 3,
> +    EVENT_CLASS_IO                  = 4,
> +    EVENT_CLASS_MAX
> +} EventClassIndex;
> +
> +#define EVENT_CLASS_MASK(index) (1 << (31 - index))
> +
> +typedef struct EventSource {
> +    const char *name;
> +    int irq;
> +    uint32_t mask;
> +    bool enabled;
> +} EventSource;
> +
> +static EventSource event_source[EVENT_CLASS_MAX] = {
> +    [EVENT_CLASS_INTERNAL_ERRORS]       = { .name = "internal-errors", },
> +    [EVENT_CLASS_EPOW]                  = { .name = "epow-events", },
> +    [EVENT_CLASS_HOT_PLUG]              = { .name = "hot-plug-events", },
> +    [EVENT_CLASS_IO]                    = { .name = "ibm,io-events", },
> +};
> +
> +static void rtas_event_source_register(EventClassIndex index, int irq)
> +{
> +    /* we only support 1 irq per event class at the moment */
> +    g_assert(!event_source[index].enabled);
> +    event_source[index].irq = irq;
> +    event_source[index].mask = EVENT_CLASS_MASK(index);
> +    event_source[index].enabled = true;
> +}
> 
> -void spapr_events_fdt_skel(void *fdt, uint32_t check_exception_irq)
> +void spapr_events_fdt_skel(void *fdt)
>  {
> -    uint32_t irq_ranges[] = {cpu_to_be32(check_exception_irq), cpu_to_be32(1)};
> -    uint32_t interrupts[] = {cpu_to_be32(check_exception_irq), 0};
> +    uint32_t irq_ranges[EVENT_CLASS_MAX * 2];
> +    int i, count = 0;
> 
>      _FDT((fdt_begin_node(fdt, "event-sources")));
> 
> +    for (i = 0, count = 0; i < EVENT_CLASS_MAX; i++) {
> +        /* TODO: what does 0 entail? */
> +        uint32_t interrupts[] = { cpu_to_be32(event_source[i].irq), 0 };
> +
> +        if (!event_source[i].enabled) {
> +            continue;
> +        }
> +
> +        _FDT((fdt_begin_node(fdt, event_source[i].name)));
> +        _FDT((fdt_property(fdt, "interrupts", interrupts, sizeof(interrupts))));
> +        _FDT((fdt_end_node(fdt)));
> +
> +        irq_ranges[count++] = interrupts[0];
> +        irq_ranges[count++] = cpu_to_be32(1);
> +    }
> +
> +    /* TODO: confirm the count is the last expected element */
> +    irq_ranges[count] = cpu_to_be32(count);
> +    count++;
> +
>      _FDT((fdt_property(fdt, "interrupt-controller", NULL, 0)));
>      _FDT((fdt_property_cell(fdt, "#interrupt-cells", 2)));
>      _FDT((fdt_property(fdt, "interrupt-ranges",
> -                       irq_ranges, sizeof(irq_ranges))));
> +                       irq_ranges, count * sizeof(uint32_t))));
> 
> -    _FDT((fdt_begin_node(fdt, "epow-events")));
> -    _FDT((fdt_property(fdt, "interrupts", interrupts, sizeof(interrupts))));
>      _FDT((fdt_end_node(fdt)));
> +}
> 
> -    _FDT((fdt_end_node(fdt)));
> +static const EventSource *rtas_event_log_to_source(int log_type)
> +{
> +    const EventSource *source;
> +
> +    switch (log_type) {
> +        case RTAS_LOG_TYPE_HOTPLUG:
> +            source = &event_source[EVENT_CLASS_HOT_PLUG];
> +            if (event_source[EVENT_CLASS_HOT_PLUG].enabled) {
> +                break;
> +            }

In addition to the above .enabled check, shouldn't you be checking if
the guest indeed supports the dedicated hotplug interrupt source before
returning the source ?

This I believe is the reason for the CPU hotplug failures I that mentioned
in reply to your 11/11 thread. I am on 4.7.x kernel which probably doesn't
support hotplug interrupt source, but QEMU ends up registering and raising
such an interrupt.

Regards,
Bharata.