[v7,12/20] exec: keep ram block across fork when using qtest

Commit Message

Alexander Bulekov Jan. 20, 2020, 5:54 a.m. UTC

Ram blocks were marked MADV_DONTFORK breaking fuzzing-tests which
execute each test-input in a forked process.

Signed-off-by: Alexander Bulekov <[e-mail]>
---
 exec.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Stefan Hajnoczi Jan. 21, 2020, 4:29 p.m. UTC | #1

On Mon, Jan 20, 2020 at 05:54:59AM +0000, Bulekov, Alexander wrote:
> Ram blocks were marked MADV_DONTFORK breaking fuzzing-tests which
> execute each test-input in a forked process.
> 
> Signed-off-by: Alexander Bulekov <[e-mail]>
> ---
>  exec.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)

Reviewed-by: Stefan Hajnoczi <[e-mail]>

Patch

diff --git a/exec.c b/exec.c
index d4b769d0d4..99368f175b 100644
--- a/exec.c
+++ b/exec.c
@@ -35,6 +35,7 @@ 
 #include "sysemu/kvm.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/tcg.h"
+#include "sysemu/qtest.h"
 #include "qemu/timer.h"
 #include "qemu/config-file.h"
 #include "qemu/error-report.h"
@@ -2306,8 +2307,15 @@  static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
     if (new_block->host) {
         qemu_ram_setup_dump(new_block->host, new_block->max_length);
         qemu_madvise(new_block->host, new_block->max_length, QEMU_MADV_HUGEPAGE);
-        /* MADV_DONTFORK is also needed by KVM in absence of synchronous MMU */
-        qemu_madvise(new_block->host, new_block->max_length, QEMU_MADV_DONTFORK);
+        /*
+         * MADV_DONTFORK is also needed by KVM in absence of synchronous MMU
+         * Configure it unless the machine is a qtest server, in which case
+         * KVM is not used and it may be forked (eg for fuzzing purposes).
+         */
+        if (!qtest_enabled()) {
+            qemu_madvise(new_block->host, new_block->max_length,
+                         QEMU_MADV_DONTFORK);
+        }
         ram_block_notify_add(new_block->host, new_block->max_length);
     }
 }