qemu-kvm/kvm-clear-out-KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT-for.patch

From fece44d5054ef13f483d7531a8462cb7f8ff5b93 Mon Sep 17 00:00:00 2001
From: Bandan Das <bsd@redhat.com>
Date: Fri, 14 Dec 2018 19:33:40 +0000
Subject: [PATCH 7/8] kvm: clear out KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT for
 older machine types

RH-Author: Bandan Das <bsd@redhat.com>
Message-id: <jpgmup79a3v.fsf@linux.bootlegged.copy>
Patchwork-id: 83523
O-Subject: [RHEL8 qemu-kvm PATCH] kvm: clear out KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT for older machine types
Bugzilla: 1659604
RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
RH-Acked-by: Pankaj Gupta <pagupta@redhat.com>
RH-Acked-by: Eduardo Habkost <ehabkost@redhat.com>

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1659604
Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=19521246
Upstream: Not applicable
Branch: rhel8/master-3.1.0 on top of [RHEL8 qemu-kvm PATCH v3 0/5] 8.0.0 x86 machine types

After the addition of support for async pf injection to L1, newer
hypervisors  advertise the feature using bit 2 of the
MSR_KVM_ASYNC_PF_EN msr. However, this was reserved in older
hypervisors which results in an error during migration like so:

qemu-kvm: error: failed to set MSR 0x4b564d02 to 0x27fc13285
qemu-kvm: /builddir/build/BUILD/qemu-2.12.0/target/i386/kvm.c:1940: kvm_put_msrs: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed.
Aborted (core dumped)

This patch introduces a new bool that is set for older machine types.
When set, Qemu's stored value clears out bit 2. This should be safe
because the guest can still enable it by writing to the MSR after
checking for support. A reset/migration for <7.6 machine type would
reset the bit though.

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 hw/i386/pc.c        | 1 +
 hw/i386/pc_piix.c   | 1 +
 hw/i386/pc_q35.c    | 1 +
 include/hw/boards.h | 2 ++
 target/i386/kvm.c   | 4 ++++
 5 files changed, 9 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index a609332..18268d3 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -2391,6 +2391,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     pcmc->linuxboot_dma_enabled = true;
     assert(!mc->get_hotplug_handler);
     pcmc->pc_rom_ro = true;
+    mc->async_pf_vmexit_disable = false;
     mc->get_hotplug_handler = pc_get_hotpug_handler;
     mc->cpu_index_to_instance_props = pc_cpu_index_to_props;
     mc->get_default_cpu_node_id = pc_get_default_cpu_node_id;
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index efee5e7..46c494a 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -1186,6 +1186,7 @@ static void pc_machine_rhel760_options(MachineClass *m)
 {
     pc_machine_rhel7_options(m);
     m->desc = "RHEL 7.6.0 PC (i440FX + PIIX, 1996)";
+    m->async_pf_vmexit_disable = true;
     SET_MACHINE_COMPAT(m, PC_RHEL7_6_COMPAT);
 }
 
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 0b7223f..1810cf2 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -470,6 +470,7 @@ static void pc_q35_machine_rhel760_options(MachineClass *m)
     pc_q35_machine_rhel800_options(m);
     m->alias = NULL;
     m->desc = "RHEL-7.6.0 PC (Q35 + ICH9, 2009)";
+    m->async_pf_vmexit_disable = true;
     SET_MACHINE_COMPAT(m, PC_RHEL7_6_COMPAT);
 }
 
diff --git a/include/hw/boards.h b/include/hw/boards.h
index f82f284..27463fb 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -204,6 +204,8 @@ struct MachineClass {
     const char **valid_cpu_types;
     strList *allowed_dynamic_sysbus_devices;
     bool auto_enable_numa_with_memhp;
+    /* RHEL only */
+    bool async_pf_vmexit_disable;
     void (*numa_auto_assign_ram)(MachineClass *mc, NodeInfo *nodes,
                                  int nb_nodes, ram_addr_t size);
     bool ignore_boot_device_suffixes;
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index b2401d1..5b0ce82 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -2351,6 +2351,7 @@ static int kvm_get_msrs(X86CPU *cpu)
     struct kvm_msr_entry *msrs = cpu->kvm_msr_buf->entries;
     int ret, i;
     uint64_t mtrr_top_bits;
+    MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
 
     kvm_msr_buf_reset(cpu);
 
@@ -2648,6 +2649,9 @@ static int kvm_get_msrs(X86CPU *cpu)
             break;
         case MSR_KVM_ASYNC_PF_EN:
             env->async_pf_en_msr = msrs[i].data;
+            if (mc->async_pf_vmexit_disable) {
+                env->async_pf_en_msr &= ~(1ULL << 2);
+            }
             break;
         case MSR_KVM_PV_EOI_EN:
             env->pv_eoi_en_msr = msrs[i].data;
-- 
1.8.3.1