Re: [Qemu-devel] [PATCH v1] kvm: tolerate non-existing slot for log_start and log_stop

[David Hildenbrand <david@redhat.com>]

On 16.10.2017 11:41, David Hildenbrand wrote:
> log_start might be called by memory.c just before registering the
> section. So we can actually get a log_start without a region_add, which
> we can silently ignore.
> 
> This makes current KVM code trigger an assertion
> ("kvm_section_update_flags: error finding slot").
> 
> Also, if we want to trap every access to a section, we might not have a
> slot. So let's just tolerate if we don't have a slot.
> 
> Fixes: 343562e8fa22 ("kvm: kvm_log_start/stop are only called with known sections")
> Reported-by: Thomas Huth <thuth@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  accel/kvm/kvm-all.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 90c88b517d..64de8461e0 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -394,8 +394,11 @@ static int kvm_section_update_flags(KVMMemoryListener *kml,
>  
>      mem = kvm_lookup_matching_slot(kml, start_addr, size);
>      if (!mem) {
> -        fprintf(stderr, "%s: error finding slot\n", __func__);
> -        abort();
> +        /*
> +         * log_start() might be called before region_add(), and sometimes
> +         * we don't have a slot as we want to trap every access.
> +         */
> +        return 0;
>      }
>  
>      return kvm_slot_update_flags(kml, mem, section->mr);
> 

I'll also send a patch for log_sync(), dropping the same assert.

Looks like adding these assertions was counter productive :)

-- 

Thanks,

David