Re: [Qemu-devel] [PATCH for-2.11 v2] hw/ppc: CAS reset on early device hotplug

2017-08-29 Thread David Gibson 
On Fri, Aug 25, 2017 at 06:11:18PM -0300, Daniel Henrique Barboza wrote:
> v2:
> - rebased with ppc-for-2.11
> - function 'spapr_cas_completed' dropped
> - function 'spapr_drc_needed' made public and it's now used inside
>   'spapr_hotplugged_dev_before_cas'
> - 'spapr_drc_needed' was changed to support the migration of logical
>   DRCs with devs attached in UNUSED state
> - new function: 'spapr_clear_pending_events'. This function is used
>   inside ppc_spapr_reset to reset the pending_events QTAILQ

Thanks for the followup, unfortunately there is still an important bug
left, see comments on the patch itself.

At a higher level, though, looking at the event reset code made me
think of a possible even simpler solution to this problem.

The queue of events (both hotplug and epow) is already in a simple
internal form that's independent of the two delivery mechanisms.  The
only difference is what event source triggers the interrupt.  This
explains why an extra hotplug event after the CAS "unstuck" the queue.

AFAICT, a spurious interrupts here should be harmless - the kernel
will just check the queue and find nothing there.

So, it should be sufficient to, after CAS, pulse the hotplug queue
interrupt if the hotplug queue is negotiated.

-- 
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

Re: [Qemu-devel] [PATCH for-2.11 v2] hw/ppc: CAS reset on early device hotplug

2017-08-29 Thread David Gibson 
On Fri, Aug 25, 2017 at 06:11:19PM -0300, Daniel Henrique Barboza wrote:
> This patch is a follow up on the discussions made in patch
> "hw/ppc: disable hotplug before CAS is completed" that can be
> found at [1].
> 
> At this moment, we do not support CPU/memory hotplug in early
> boot stages, before CAS. When a hotplug occurs, the event is logged
> in an internal RTAS event log queue and an IRQ pulse is fired. In
> regular conditions, the guest handles the interrupt by executing
> check_exception, fetching the generated hotplug event and enabling
> the device for use.
> 
> In early boot, this IRQ isn't caught (SLOF does not handle hotplug
> events), leaving the event in the rtas event log queue. If the guest
> executes check_exception due to another hotplug event, the re-assertion
> of the IRQ ends up de-queuing the first hotplug event as well. In short,
> a device hotplugged before CAS is considered coldplugged by SLOF.
> This leads to device misbehavior and, in some cases, guest kernel
> Ooops when trying to unplug the device.
> 
> A proper fix would be to turn every device hotplugged before CAS
> as a colplugged device. This is not trivial to do with the current
> code base though - the FDT is written in the guest memory at
> ppc_spapr_reset and can't be retrieved without adding extra state
> (fdt_size for example) that will need to managed and migrated. Adding
> the hotplugged DT in the middle of CAS negotiation via the updated DT
> tree works with CPU devs, but panics the guest kernel at boot. Additional
> analysis would be necessary for LMBs and PCI devices. There are
> questions to be made in QEMU/SLOF/kernel level about how we can make
> this change in a sustainable way.
> 
> Until we go all the way with the proper fix, this patch works around
> the situation by issuing a CAS reset if a hotplugged device is detected
> during CAS:
> 
> - the DRC conditions that warrant a CAS reset is the same as those that
> triggers a DRC migration - the DRC must have a device attached and
> the DRC state is not equal to its ready_state. With that in mind, this
> patch makes use of 'spapr_drc_needed' to determine if a CAS reset
> is needed.
> 
> - In the middle of CAS negotiations, the function
> 'spapr_hotplugged_dev_before_cas' goes through all the DRCs to see
> if there are any DRC that requires a reset, using spapr_drc_needed. If
> that happens, returns '1' in 'spapr_h_cas_compose_response' which will set
> spapr->cas_reboot to true, causing the machine to reboot.
> 
> - a small fix was made in 'spapr_drc_needed' to change how we detect
> a DRC device. Using dr_entity_sense worked for physical DRCs but,
> for logical DRCs, it didn't cover the case where a logical DRC has
> a drc->dev but the state is LOGICAL_UNUSABLE (e.g. a hotplugged CPU before
> CAS). In this case, the dr_entity_sense of this DRC returns UNUSABLE and
> spapr_drc_needed was return 'false' for a scenario what we would like
> to migrate the DRC (or issue a CAS reset). Changing it to check for
> drc->dev instead works for all DRC types.
> 
> - a new function called 'spapr_clear_pending_events' was created
> and is being called inside ppc_spapr_reset. This function clears
> the pending_events QTAILQ that holds the RTAS event logs. This prevents
> old/deprecated events from persisting after a reset.
> 
> No changes are made for coldplug devices.
> 
> [1] http://lists.nongnu.org/archive/html/qemu-devel/2017-08/msg02855.html
> 
> Signed-off-by: Daniel Henrique Barboza 

Sorry I've taken a while to review.

> ---
>  hw/ppc/spapr.c | 34 ++
>  hw/ppc/spapr_drc.c |  5 ++---
>  include/hw/ppc/spapr_drc.h |  1 +
>  3 files changed, 37 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index fb1e5e0..4b23ad3 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -790,6 +790,26 @@ out:
>  return ret;
>  }
>  
> +static bool spapr_hotplugged_dev_before_cas(void)
> +{
> +Object *drc_container, *obj;
> +ObjectProperty *prop;
> +ObjectPropertyIterator iter;
> +
> +drc_container = container_get(object_get_root(), "/dr-connector");
> +object_property_iter_init(, drc_container);
> +while ((prop = object_property_iter_next())) {
> +if (!strstart(prop->type, "link<", NULL)) {
> +continue;
> +}
> +obj = object_property_get_link(drc_container, prop->name, NULL);
> +if (spapr_drc_needed(obj)) {
> +return true;
> +}
> +}
> +return false;
> +}
> +
>  int spapr_h_cas_compose_response(sPAPRMachineState *spapr,
>   target_ulong addr, target_ulong size,
>   sPAPROptionVector *ov5_updates)
> @@ -797,6 +817,10 @@ int spapr_h_cas_compose_response(sPAPRMachineState 
> *spapr,
>  void *fdt, *fdt_skel;
>  sPAPRDeviceTreeUpdateHeader hdr = { .version_id = 1 };
>  
> +if

[Qemu-devel] [PATCH for-2.11 v2] hw/ppc: CAS reset on early device hotplug

2017-08-25 Thread Daniel Henrique Barboza 
This patch is a follow up on the discussions made in patch
"hw/ppc: disable hotplug before CAS is completed" that can be
found at [1].

At this moment, we do not support CPU/memory hotplug in early
boot stages, before CAS. When a hotplug occurs, the event is logged
in an internal RTAS event log queue and an IRQ pulse is fired. In
regular conditions, the guest handles the interrupt by executing
check_exception, fetching the generated hotplug event and enabling
the device for use.

In early boot, this IRQ isn't caught (SLOF does not handle hotplug
events), leaving the event in the rtas event log queue. If the guest
executes check_exception due to another hotplug event, the re-assertion
of the IRQ ends up de-queuing the first hotplug event as well. In short,
a device hotplugged before CAS is considered coldplugged by SLOF.
This leads to device misbehavior and, in some cases, guest kernel
Ooops when trying to unplug the device.

A proper fix would be to turn every device hotplugged before CAS
as a colplugged device. This is not trivial to do with the current
code base though - the FDT is written in the guest memory at
ppc_spapr_reset and can't be retrieved without adding extra state
(fdt_size for example) that will need to managed and migrated. Adding
the hotplugged DT in the middle of CAS negotiation via the updated DT
tree works with CPU devs, but panics the guest kernel at boot. Additional
analysis would be necessary for LMBs and PCI devices. There are
questions to be made in QEMU/SLOF/kernel level about how we can make
this change in a sustainable way.

Until we go all the way with the proper fix, this patch works around
the situation by issuing a CAS reset if a hotplugged device is detected
during CAS:

- the DRC conditions that warrant a CAS reset is the same as those that
triggers a DRC migration - the DRC must have a device attached and
the DRC state is not equal to its ready_state. With that in mind, this
patch makes use of 'spapr_drc_needed' to determine if a CAS reset
is needed.

- In the middle of CAS negotiations, the function
'spapr_hotplugged_dev_before_cas' goes through all the DRCs to see
if there are any DRC that requires a reset, using spapr_drc_needed. If
that happens, returns '1' in 'spapr_h_cas_compose_response' which will set
spapr->cas_reboot to true, causing the machine to reboot.

- a small fix was made in 'spapr_drc_needed' to change how we detect
a DRC device. Using dr_entity_sense worked for physical DRCs but,
for logical DRCs, it didn't cover the case where a logical DRC has
a drc->dev but the state is LOGICAL_UNUSABLE (e.g. a hotplugged CPU before
CAS). In this case, the dr_entity_sense of this DRC returns UNUSABLE and
spapr_drc_needed was return 'false' for a scenario what we would like
to migrate the DRC (or issue a CAS reset). Changing it to check for
drc->dev instead works for all DRC types.

- a new function called 'spapr_clear_pending_events' was created
and is being called inside ppc_spapr_reset. This function clears
the pending_events QTAILQ that holds the RTAS event logs. This prevents
old/deprecated events from persisting after a reset.

No changes are made for coldplug devices.

[1] http://lists.nongnu.org/archive/html/qemu-devel/2017-08/msg02855.html

Signed-off-by: Daniel Henrique Barboza 
---
 hw/ppc/spapr.c | 34 ++
 hw/ppc/spapr_drc.c |  5 ++---
 include/hw/ppc/spapr_drc.h |  1 +
 3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index fb1e5e0..4b23ad3 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -790,6 +790,26 @@ out:
 return ret;
 }
 
+static bool spapr_hotplugged_dev_before_cas(void)
+{
+Object *drc_container, *obj;
+ObjectProperty *prop;
+ObjectPropertyIterator iter;
+
+drc_container = container_get(object_get_root(), "/dr-connector");
+object_property_iter_init(, drc_container);
+while ((prop = object_property_iter_next())) {
+if (!strstart(prop->type, "link<", NULL)) {
+continue;
+}
+obj = object_property_get_link(drc_container, prop->name, NULL);
+if (spapr_drc_needed(obj)) {
+return true;
+}
+}
+return false;
+}
+
 int spapr_h_cas_compose_response(sPAPRMachineState *spapr,
  target_ulong addr, target_ulong size,
  sPAPROptionVector *ov5_updates)
@@ -797,6 +817,10 @@ int spapr_h_cas_compose_response(sPAPRMachineState *spapr,
 void *fdt, *fdt_skel;
 sPAPRDeviceTreeUpdateHeader hdr = { .version_id = 1 };
 
+if (spapr_hotplugged_dev_before_cas()) {
+return 1;
+}
+
 size -= sizeof(hdr);
 
 /* Create sceleton */
@@ -1369,6 +1393,15 @@ static void find_unknown_sysbus_device(SysBusDevice 
*sbdev, void *opaque)
 }
 }
 
+static void spapr_clear_pending_events(sPAPRMachineState *spapr)
+{
+sPAPREventLogEntry *entry = NULL;
+
+

[Qemu-devel] [PATCH for-2.11 v2] hw/ppc: CAS reset on early device hotplug

2017-08-25 Thread Daniel Henrique Barboza 
v2:
- rebased with ppc-for-2.11
- function 'spapr_cas_completed' dropped
- function 'spapr_drc_needed' made public and it's now used inside
  'spapr_hotplugged_dev_before_cas'
- 'spapr_drc_needed' was changed to support the migration of logical
  DRCs with devs attached in UNUSED state
- new function: 'spapr_clear_pending_events'. This function is used
  inside ppc_spapr_reset to reset the pending_events QTAILQ

Daniel Henrique Barboza (1):
  hw/ppc: CAS reset on early device hotplug

 hw/ppc/spapr.c | 34 ++
 hw/ppc/spapr_drc.c |  5 ++---
 include/hw/ppc/spapr_drc.h |  1 +
 3 files changed, 37 insertions(+), 3 deletions(-)

-- 
2.9.4