Re: [PATCH v8 12/21] exec: keep ram block across fork when using qtest

[Darren Kenny]

On Wed, Jan 29, 2020 at 05:34:21AM +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 <address@hidden>
> Reviewed-by: Stefan Hajnoczi <address@hidden>

Reviewed-by: Darren Kenny <address@hidden>

> ---
> exec.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> 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);
>     }
> }
> --
> 2.23.0