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[Qemu-devel] [PATCH v2] accel: forbid early use of kvm_enabled() and fri


From: Greg Kurz
Subject: [Qemu-devel] [PATCH v2] accel: forbid early use of kvm_enabled() and friends
Date: Fri, 29 Jun 2018 12:29:34 +0200
User-agent: StGit/0.17.1-46-g6855-dirty

It is unsafe to rely on *_enabled() helpers before the accelerator has
been initialized, ie, accel_init_machine() has succeeded, because they
always return false. But it is still possible to end up calling them
indirectly by inadvertance, and cause QEMU to misbehave.

This patch causes QEMU to abort if we try to check for an accelerator
before it has been set up. This will help to catch bugs earlier.

Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: David Gibson <address@hidden>
---

This patch was motivated by an regression we're currently fixing in
spapr because of an early use of kvm_enabled(). David suggested to
post this patch separately:

https://lists.nongnu.org/archive/html/qemu-ppc/2018-06/msg01136.html

v2: - dropped change in qom/cpu.c (useless header inclusion)
    - only #include "sysemu/kvm.h" if we actually need it
    - added David's R-b from v1 because changes in v2 are minor
---
 accel/accel.c          |    7 +++++++
 include/qemu-common.h  |    3 ++-
 include/sysemu/accel.h |    1 +
 include/sysemu/kvm.h   |    3 ++-
 stubs/Makefile.objs    |    1 +
 stubs/accel.c          |   14 ++++++++++++++
 target/i386/hax-all.c  |    2 +-
 target/i386/whpx-all.c |    2 +-
 8 files changed, 29 insertions(+), 4 deletions(-)
 create mode 100644 stubs/accel.c

diff --git a/accel/accel.c b/accel/accel.c
index 966b2d8f536c..27900aac9cc5 100644
--- a/accel/accel.c
+++ b/accel/accel.c
@@ -51,6 +51,13 @@ static AccelClass *accel_find(const char *opt_name)
     return ac;
 }
 
+bool assert_accelerator_initialized(bool allowed)
+{
+    assert(current_machine != NULL);
+    assert(current_machine->accelerator != NULL);
+    return allowed;
+}
+
 static int accel_init_machine(AccelClass *acc, MachineState *ms)
 {
     ObjectClass *oc = OBJECT_CLASS(acc);
diff --git a/include/qemu-common.h b/include/qemu-common.h
index 85f4749aefb7..01d5e4d97dbf 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -82,7 +82,8 @@ int qemu_openpty_raw(int *aslave, char *pty_name);
 extern bool tcg_allowed;
 void tcg_exec_init(unsigned long tb_size);
 #ifdef CONFIG_TCG
-#define tcg_enabled() (tcg_allowed)
+#include "sysemu/accel.h"
+#define tcg_enabled() (assert_accelerator_initialized(tcg_allowed))
 #else
 #define tcg_enabled() 0
 #endif
diff --git a/include/sysemu/accel.h b/include/sysemu/accel.h
index 637358f43014..76965cb69cc9 100644
--- a/include/sysemu/accel.h
+++ b/include/sysemu/accel.h
@@ -71,5 +71,6 @@ void configure_accelerator(MachineState *ms);
 void accel_register_compat_props(AccelState *accel);
 /* Called just before os_setup_post (ie just before drop OS privs) */
 void accel_setup_post(MachineState *ms);
+bool assert_accelerator_initialized(bool allowed);
 
 #endif
diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index 0b64b8e06786..5a2e59e99128 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -46,7 +46,8 @@ extern bool kvm_direct_msi_allowed;
 extern bool kvm_ioeventfd_any_length_allowed;
 extern bool kvm_msi_use_devid;
 
-#define kvm_enabled()           (kvm_allowed)
+#include "sysemu/accel.h"
+#define kvm_enabled()           (assert_accelerator_initialized(kvm_allowed))
 /**
  * kvm_irqchip_in_kernel:
  *
diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index 53d3f32cb258..2d5142287525 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -43,3 +43,4 @@ stub-obj-y += xen-common.o
 stub-obj-y += xen-hvm.o
 stub-obj-y += pci-host-piix.o
 stub-obj-y += ram-block.o
+stub-obj-y += accel.o
diff --git a/stubs/accel.c b/stubs/accel.c
new file mode 100644
index 000000000000..4f480f2d3f29
--- /dev/null
+++ b/stubs/accel.c
@@ -0,0 +1,14 @@
+/*
+ * accel stubs
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "sysemu/accel.h"
+
+bool assert_accelerator_initialized(bool allowed)
+{
+    return allowed;
+}
diff --git a/target/i386/hax-all.c b/target/i386/hax-all.c
index d2e512856bb8..7c78bd7d094d 100644
--- a/target/i386/hax-all.c
+++ b/target/i386/hax-all.c
@@ -57,7 +57,7 @@ static int hax_arch_get_registers(CPUArchState *env);
 
 int hax_enabled(void)
 {
-    return hax_allowed;
+    return assert_accelerator_initialized(hax_allowed);
 }
 
 int valid_hax_tunnel_size(uint16_t size)
diff --git a/target/i386/whpx-all.c b/target/i386/whpx-all.c
index 6b42096698ee..e7f6bc5958e7 100644
--- a/target/i386/whpx-all.c
+++ b/target/i386/whpx-all.c
@@ -1422,7 +1422,7 @@ static int whpx_accel_init(MachineState *ms)
 
 int whpx_enabled(void)
 {
-    return whpx_allowed;
+    return assert_accelerator_initialized(whpx_allowed);
 }
 
 static void whpx_accel_class_init(ObjectClass *oc, void *data)




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