Re: [Xen-devel] [PATCH] x86/monitor: Disallow setting mem_access_emulate_each_rep when vm_event is NULL

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 04/08/16 10:10, Razvan Cojocaru wrote:
> It is meaningless (and potentially dangerous - see 
> hvmemul_virtual_to_linear())
> to set mem_access_emulate_each_rep before xc_monitor_enable() (which allocates
> vcpu->arch.vm_event) has been called, so return an error from the
> XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP hypercall when that is the case.
> 
> Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> ---
>  xen/include/asm-x86/monitor.h | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/include/asm-x86/monitor.h b/xen/include/asm-x86/monitor.h
> index 0954b59..0544836 100644
> --- a/xen/include/asm-x86/monitor.h
> +++ b/xen/include/asm-x86/monitor.h
> @@ -35,11 +35,22 @@ int arch_monitor_domctl_op(struct domain *d, struct 
> xen_domctl_monitor_op *mop)
>      switch ( mop->op )
>      {
>      case XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP:
> +    {
> +        bool_t value = !!mop->event;
>          domain_pause(d);
> -        d->arch.mem_access_emulate_each_rep = !!mop->event;
> +        /*
> +         * Enabling emulate_each_rep without a vm_event subscriber
> +         * is meaningless.
> +         */
> +        if ( !d->vcpu || !d->vcpu[0]->arch.vm_event )

Sorry, this is a bit convoluted, and wrong: if d->vcpu != NULL it will
return -EINVAL even if d->vcpu[0]->arch.vm_event is NULL. I'll rework
it. Apologies for the noise.


Thanks,
Razvan

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