Re: [PATCH v2 03/19] accel/kvm: Convert to ram_block_discard_disable()

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi David,

On 5/20/20 2:31 PM, David Hildenbrand wrote:
> Discarding memory does not work as expected. At the time this is called,
> we cannot have anyone active that relies on discards to work properly.
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   accel/kvm/kvm-all.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index d06cc04079..7a6158fb99 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -40,7 +40,6 @@
>   #include "trace.h"
>   #include "hw/irq.h"
>   #include "sysemu/sev.h"
> -#include "sysemu/balloon.h"
>   #include "qapi/visitor.h"
>   #include "qapi/qapi-types-common.h"
>   #include "qapi/qapi-visit-common.h"
> @@ -2143,7 +2142,7 @@ static int kvm_init(MachineState *ms)
>   
>       s->sync_mmu = !!kvm_vm_check_extension(kvm_state, KVM_CAP_SYNC_MMU);
>       if (!s->sync_mmu) {
> -        qemu_balloon_inhibit(true);
> +        g_assert(ram_block_discard_disable(true));

Please do not evaluate code within an assert() call.

See the comment added to "qemu/osdep.h" in commit 262a69f4282:

/*
  * We have a lot of unaudited code that may fail in strange ways, or
  * even be a security risk during migration, if you disable assertions
  * at compile-time.  You may comment out these safety checks if you
  * absolutely want to disable assertion overhead, but it is not
  * supported upstream so the risk is all yours.  Meanwhile, please
  * submit patches to remove any side-effects inside an assertion, or
  * fixing error handling that should use Error instead of assert.
  */

>       }
>   
>       return 0;
>