From f94b3a4eb9d709f1f6a14ad9ad6ebcc1b67b6923 Mon Sep 17 00:00:00 2001
From: Greg Kurz <gkurz@redhat.com>
Date: Tue, 19 Jan 2021 15:09:54 -0500
Subject: [PATCH 6/9] spapr: Improve handling of memory unplug with old guests

RH-Author: Greg Kurz <gkurz@redhat.com>
Message-id: <20210119150954.1017058-7-gkurz@redhat.com>
Patchwork-id: 100684
O-Subject: [RHEL-8.4.0 qemu-kvm PATCH v2 6/6] spapr: Improve handling of memory unplug with old guests
Bugzilla: 1901837
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
RH-Acked-by: David Gibson <dgibson@redhat.com>

From: Greg Kurz <groug@kaod.org>

Since commit 1e8b5b1aa16b ("spapr: Allow memory unplug to always succeed")
trying to unplug memory from a guest that doesn't support it (eg. rhel6)
no longer generates an error like it used to. Instead, it leaves the
memory around : only a subsequent reboot or manual use of drmgr within
the guest can complete the hot-unplug sequence. A flag was added to
SpaprMachineClass so that this new behavior only applies to the default
machine type.

We can do better. CAS processes all pending hot-unplug requests. This
means that we don't really care about what the guest supports if
the hot-unplug request happens before CAS.

All guests that we care for, even old ones, set enough bits in OV5
that lead to a non-empty bitmap in spapr->ov5_cas. Use that as a
heuristic to decide if CAS has already occured or not.

Always accept unplug requests that happen before CAS since CAS will
process them. Restore the previous behavior of rejecting them after
CAS when we know that the guest doesn't support memory hot-unplug.

This behavior is suitable for all machine types : this allows to
drop the pre_6_0_memory_unplug flag.

Fixes: 1e8b5b1aa16b ("spapr: Allow memory unplug to always succeed")
Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <161012708715.801107.11418801796987916516.stgit@bahia.lan>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
(cherry picked from commit 73598c75df0585e039825e642adede21912dabc7)
Signed-off-by: Greg Kurz <gkurz@redhat.com>

Conflicts:
	hw/ppc/spapr.c
	include/hw/ppc/spapr.h

Contextual conflicts around the removal of pre_6_0_memory_unplug,
which was only partially backported from upstream 1e8b5b1aa16b, and
the addition of spapr_memory_hot_unplug_supported().

Signed-off-by: Jon Maloy <jmaloy.redhat.com>
---
 hw/ppc/spapr.c              | 21 +++++++++++++--------
 hw/ppc/spapr_events.c       |  3 +--
 hw/ppc/spapr_ovec.c         |  7 +++++++
 include/hw/ppc/spapr.h      |  2 +-
 include/hw/ppc/spapr_ovec.h |  1 +
 5 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index f8de33e3e5..00b1ef075e 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3993,6 +3993,18 @@ static void spapr_machine_device_unplug(HotplugHandler *hotplug_dev,
     }
 }
 
+bool spapr_memory_hot_unplug_supported(SpaprMachineState *spapr)
+{
+    return spapr_ovec_test(spapr->ov5_cas, OV5_HP_EVT) ||
+        /*
+         * CAS will process all pending unplug requests.
+         *
+         * HACK: a guest could theoretically have cleared all bits in OV5,
+         * but none of the guests we care for do.
+         */
+        spapr_ovec_empty(spapr->ov5_cas);
+}
+
 static void spapr_machine_device_unplug_request(HotplugHandler *hotplug_dev,
                                                 DeviceState *dev, Error **errp)
 {
@@ -4001,16 +4013,9 @@ static void spapr_machine_device_unplug_request(HotplugHandler *hotplug_dev,
     SpaprMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
 
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
-        if (!smc->pre_6_0_memory_unplug ||
-            spapr_ovec_test(sms->ov5_cas, OV5_HP_EVT)) {
+        if (spapr_memory_hot_unplug_supported(sms)) {
             spapr_memory_unplug_request(hotplug_dev, dev, errp);
         } else {
-            /* NOTE: this means there is a window after guest reset, prior to
-             * CAS negotiation, where unplug requests will fail due to the
-             * capability not being detected yet. This is a bit different than
-             * the case with PCI unplug, where the events will be queued and
-             * eventually handled by the guest after boot
-             */
             error_setg(errp, "Memory hot unplug not supported for this guest");
         }
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_SPAPR_CPU_CORE)) {
diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
index 6e284aa4bc..08168acd65 100644
--- a/hw/ppc/spapr_events.c
+++ b/hw/ppc/spapr_events.c
@@ -547,8 +547,7 @@ static void spapr_hotplug_req_event(uint8_t hp_id, uint8_t hp_action,
         /* we should not be using count_indexed value unless the guest
          * supports dedicated hotplug event source
          */
-        g_assert(!SPAPR_MACHINE_GET_CLASS(spapr)->pre_6_0_memory_unplug ||
-                 spapr_ovec_test(spapr->ov5_cas, OV5_HP_EVT));
+        g_assert(spapr_memory_hot_unplug_supported(spapr));
         hp->drc_id.count_indexed.count =
             cpu_to_be32(drc_id->count_indexed.count);
         hp->drc_id.count_indexed.index =
diff --git a/hw/ppc/spapr_ovec.c b/hw/ppc/spapr_ovec.c
index 811fadf143..f858afc7d5 100644
--- a/hw/ppc/spapr_ovec.c
+++ b/hw/ppc/spapr_ovec.c
@@ -135,6 +135,13 @@ bool spapr_ovec_test(SpaprOptionVector *ov, long bitnr)
     return test_bit(bitnr, ov->bitmap) ? true : false;
 }
 
+bool spapr_ovec_empty(SpaprOptionVector *ov)
+{
+    g_assert(ov);
+
+    return bitmap_empty(ov->bitmap, OV_MAXBITS);
+}
+
 static void guest_byte_to_bitmap(uint8_t entry, unsigned long *bitmap,
                                  long bitmap_offset)
 {
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index ac6961ed16..7aaf5d9996 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -124,7 +124,6 @@ struct SpaprMachineClass {
     bool pre_4_1_migration; /* don't migrate hpt-max-page-size */
     bool linux_pci_probe;
     bool smp_threads_vsmt; /* set VSMT to smp_threads by default */
-    bool pre_6_0_memory_unplug;
 
     bool has_power9_support;
     void (*phb_placement)(SpaprMachineState *spapr, uint32_t index,
@@ -894,4 +893,5 @@ void spapr_check_pagesize(SpaprMachineState *spapr, hwaddr pagesize,
 #define SPAPR_OV5_XIVE_BOTH     0x80 /* Only to advertise on the platform */
 
 void spapr_set_all_lpcrs(target_ulong value, target_ulong mask);
+bool spapr_memory_hot_unplug_supported(SpaprMachineState *spapr);
 #endif /* HW_SPAPR_H */
diff --git a/include/hw/ppc/spapr_ovec.h b/include/hw/ppc/spapr_ovec.h
index 7891e9caac..98c73bf601 100644
--- a/include/hw/ppc/spapr_ovec.h
+++ b/include/hw/ppc/spapr_ovec.h
@@ -73,6 +73,7 @@ void spapr_ovec_cleanup(SpaprOptionVector *ov);
 void spapr_ovec_set(SpaprOptionVector *ov, long bitnr);
 void spapr_ovec_clear(SpaprOptionVector *ov, long bitnr);
 bool spapr_ovec_test(SpaprOptionVector *ov, long bitnr);
+bool spapr_ovec_empty(SpaprOptionVector *ov);
 SpaprOptionVector *spapr_ovec_parse_vector(target_ulong table_addr, int vector);
 int spapr_ovec_populate_dt(void *fdt, int fdt_offset,
                            SpaprOptionVector *ov, const char *name);
-- 
2.18.2