Re: [Xen-devel] [PATCH v2 3/7] x86/vm-event/monitor: don't compromise monitor_write_data on domain cleanup

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 05/07/16 15:28, Corneliu ZUZU wrote:
> The arch_vm_event structure is dynamically allocated and freed @
> vm_event_cleanup_domain. This cleanup is triggered e.g. when the toolstack 
> user
> disables domain monitoring (xc_monitor_disable), which in turn effectively
> discards any information that was in arch_vm_event.write_data.
> 
> But this can yield unexpected behavior since if a CR-write was awaiting to be
> committed on the scheduling tail (hvm_do_resume->arch_monitor_write_data)
> before xc_monitor_disable is called, then the domain CR write is wrongfully
> ignored, which of course, in these cases, can easily render a domain crash.
> 
> To fix the issue, this patch makes arch_vm_event.emul_read_data dynamically
> allocated and only frees that in vm_event_cleanup_domain, instead of the whole
> arch_vcpu.vm_event structure, which with this patch will only be freed on
> vcpu/domain destroyal.
> 
> Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
> Acked-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>

On the basis of one of the vm_event maintainer's acks...

> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index 16733a4..6616626 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -1642,7 +1642,7 @@ void p2m_mem_access_emulate_check(struct vcpu *v,
>          v->arch.vm_event->emulate_flags = violation ? rsp->flags : 0;
>  
>          if ( (rsp->flags & VM_EVENT_FLAG_SET_EMUL_READ_DATA) )
> -            v->arch.vm_event->emul_read_data = rsp->data.emul_read_data;
> +            *v->arch.vm_event->emul_read_data = rsp->data.emul_read_data;
>      }
>  }
>  

p2m bits:

Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>


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